1. business and industrial
2. energy
3. renewable energy
4. fuel cell

Impact of catalyst support on the activity of the oxygen evolution catalyst in
PEM water electrolysis
Karel Bouzek, Jakub Polonský, Tomáš Bystroň
University of Chemistry and Technology Prague; Technická 5; 166 28 Prague 6-Dejvice
E mail: [email protected]
Even though the principle of water electrolysis has been known for more than two centuries, the
development of the related industrial process is far from being complete. The currently most
commonly used water electrolysis process is an alkaline one with KOH solution as the electrolyte. An
alternative process represents polymer electrolyte membrane (PEM) water electrolysis. In contrast
with the alkaline technology, PEM water electrolysis offers higher process efficiency and intensity. At
the same time it is suitable for intermittent operation and does not include corrosive liquid electrolyte.
However, at the current state of the art, it suffers from significant disadvantages: both electrodes are
based on precious metal electrocatalysts, the polymer electrolyte membrane is expensive and the
demands on the stability of the anode side materials are rather extreme. The research activities in the
field are focused mainly on the reduction of the precious metals load and increase in the life time of
the system.
The largest contribution to the cell activation losses is due to the anodic oxygen evolution reaction
(OER), which is much slower than the hydrogen evolution taking place at the cathode. Furthermore,
the anode has a high oxidation potential and at the same time the environment is strongly acidic;
therefore, only very few materials can survive here for sufficiently long time. Carbon, frequently used
in PEM fuel cell technology, cannot be used on the anode side of the PEM water electrolyser because
it corrodes quickly. Instead, Ti and Ta are commonly used as the materials for the anode construction.
Electrode surface is then activated by IrO2, RuO2 or their combination.
There are several ways how to increase the degree of the precious metal utilisation and thus to lower
its load required for the desired anode performance. One of them is to use a catalyst support, which
can increase the dispersion of the active phase. In the present study TaC, -SiC and TiO2 were chosen
as the catalyst supports carrying IrO2 as an active part. Motivation for this selection was two-fold.
First, these materials were identified to show sufficient chemical stability in the PEM water
electrolysis environment. Second, they allow to verify the impact of the support conductivity on the
anode catalyst activity. The samples prepared were characterized by XRD, SEM, BET, XPS and by
powder conductivity measurement. Using selected catalysts, electrodes based on Ti felt were prepared
and tested in a laboratory PEM water electrolyser. Load curves and electrochemical impedance spectra
were recorded and analysed to evaluate the best-performing catalyst.
Supported catalysts performing significantly better than unsupported IrO2, thus enabling a more
efficient electrolysis, were identified. This contribution summarizes the achieved results and highlights
some aspects of the catalyst support role in the construction of an anode for the PEM water
electrolysis.
Acknowledgement
Financial support of this study by the Grant agency of the Czech Republic within the framework of the
project No. 15-024007J is acknowledged.
Reducible oxides in low-temperature fuel cells:
model studies from surface science to spectroelectrochemistry
Jörg Libuda
Department of Chemistry and Pharmacy and Erlangen Catalysis Resource Center,
University Erlangen-Nürnberg, Erlangen, Germany
Email: [email protected]
Ceria-based catalytic materials are among the most fascinating ones in environmental and
energy technology, with applications ranging from exhaust catalysis via hydrogen production to
fuel cell technology. Their surface nanostructure is the key to control and tune their surface
reactivity. When used as supports for noble metal nanoparticles, it is the oxide nanostructure
which controls the energetics of spillover and reverse spillover processes. Very importantly, the
support nanostructure also affects the dispersion of the supported noble metal itself. In the
ultimate limit, nanostructured ceria supports even allow the preparation thermally stable
atomically-dispersed noble metal catalysts.
Following a surface-science approach, we develop a hierarchy of model systems for ceria-based
catalytic materials. We start from the preparation of ordered ceria thin films on single crystal
metal supports, and review the characterization of the film structure, the defect structure,
methods to modify the stoichiometry and methods for metal deposition and metal doping. Using
these models, detailed insights into their geometric and electronic structure, stability, adsorption
properties, and reactivity are obtained from ultrahigh vacuum to realistic reaction conditions.
The surface structure of these systems is studied, for example, studied by scanning tunneling
microscopy (STM), electronic properties are investigated by photoelectron spectroscopy (PES)
including synchrotron-radiation-based methods (SR-PES), vibrational properties are probed by
infrared reflection absorption spectroscopy (IRAS) and the adsorption and reaction kinetics is
studied using molecular beam (MB) techniques and temperature programmed desorption (TPD).
Three aspects are discussed in specific which are related to the catalytic and electro-catalytic
properties of ceria-based catalysts: The first topic is related to spillover processes, which are
important mechanistic steps in numerous catalytic reactions. The term describes the transfer of
activated reactants via phase boundaries between different regions of a nanostructured catalyst,
e.g. nanoparticles and support. For reducible oxides, spillover is often linked to the surface
redox chemistry. It is discussed how hydrogen, oxygen, hydrocarbons, and sulfur spillover can
be investigated, for example by resonant photoelectron spectroscopy (RPES) and how these
mechanistic steps relate to complex reaction mechanisms, e.g. in hydrogen production. The
second aspect is related to the stabilization of catalytically active noble metals. Noble metals
such as Pt can be stabilized on ceria surfaces in atomically dispersed form and model systems
for such atomically dispersed catalysts can be prepared using a surface science approach. These
atomically defined model systems help to explore the geometric, electronic, and chemical
properties of such systems. Finally, applications of ceria-based catalytic coatings in proton
exchange membrane fuel cells (PEM-FCs) are discussed. Here, porous coatings of Pt-doped
ceria show high noble metal efficiency and excellent stability. Comparative experiments on
model systems and thin film catalysts help to explore the related reaction mechanisms. The
reactivity of Pt-CeO2 thin films towards H2, CO, and CH3OH is studied in both ultrahigh
vacuum (UHV) and in-situ under electrochemically controlled conditions. UHV studies suggest
that hydrogen activation requires traces of metallic Pt to be present at the surface, whereas
CH3OH activation is facile, even in the absence of any metallic Pt. Subtractively normalized
interfacial Fourier Transform infrared spectroscopy (SNIFTIRS) indicates that under
electrochemically controlled conditions the ceria support helps to stabilize very small metallic
Pt aggregates which show a reduced tendency for poisoning.
In Situ and Operando Characterization of Model Catalysts at Work
Beatriz Roldan Cuenya
Department of Physics, Ruhr-University Bochum, Bochum 44780, Germany
E mail: [email protected]
In order to comprehend the properties affecting the catalytic performance of metal
nanoparticles (NPs), their dynamic nature and response to the environment must be taken into
consideration. The working state of a NP catalyst might not be the state in which the catalyst was
prepared, but a structural and/or chemical isomer that adapted to the particular reaction
conditions.
This work provides examples of recent advances in the preparation and characterization of
NP catalysts with well-defined sizes and shapes. It discusses how to resolve the shape of nmsized Pt, Au, Pd, and Cu catalysts via a combination of in situ microscopy (AFM, STM, TEM),
and in situ and operando spectroscopy (XAFS, GISAXS) and modeling, and how to follow its
evolution under different gaseous or liquid chemical environments and in the course of a reaction.
It will be highlighted that for structure-sensitive reactions, catalytic properties such as the reaction
rates, onset reaction temperature, activity, selectivity and stability against sintering may be tuned
through controlled synthesis.
Examples of catalytic processes which will be discussed include the gas-phase oxidation of
alcohols (methanol, propanol, butanol), the oxidation and reduction of NO, the electrochemical
oxidation of propanol and electrochemical reduction of CO2. Emphasis will be given to
elucidating the role of the NP size, shape and chemical state in the activity and selectivity of the
former reactions.
Computational studies of nanoparticulate models of catalysts
in the chipCAT project
Konstantin M. Neyman
Institució Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Química Física & Institut
de Química Teòrica i Computacional, Universitat de Barcelona, Barcelona, Spain
Email: [email protected]
Active metal components present in heterogeneous catalysts as nano-aggregates of thousands atoms remain
inaccessible for first-principles (based on the density-functional theory) computations due to their size.
However, such species could be rather realistically represented by computationally tractable smaller metal
nanoparticles (NPs), whose surface sites marginally change the reactivity with increasing particle size.1 We
illustrate this for Pd catalysts2-4 as well as for the building of active sites on Pt/ceria catalysts.5-7 Furthermore,
we consider Pd and Pt NPs with more than 100 atoms, supported on MgO(100).8-10 Finally, a problem of
realistic surface composition in nanoalloy catalysts11,12 is briefly discussed.
We show that employment of conventional slab models and thus neglecting the nanoscopic effects in these
and similar systems can lead to severe misrepresentation of the surface reactivity. Investigated by us
dedicated NP models expose a variety of active sites, whose structure and geometric flexibility notably better
match those of the sites present under experimental conditions. Thus, we advocate much broader usage of
suitable NP models in “catalysis from first principles”, in a fashion the NP models are employed in various
studies of the ChipCAT project.
1. S. M. Kozlov, K. M. Neyman, Top. Catal. 56, 86 (2013)
2. K. M. Neyman, S. Schauermann, Angew. Chem. Int. Ed. 49, 4743 (2010)
3. H.A. Aleksandrov, F. Viñes, W. Ludwig, S. Schauermann, K.M. Neyman, Chem. - Eur. J. 19, 1335 (2013)
4. H. A. Aleksandrov, S. M. Kozlov, S. Schauermann, G. N. Vayssilov, K. M. Neyman, Angew. Chem. Int.
Ed. 53 (2014) 13371
5. G. N. Vayssilov, Y. Lykhach, A. Migani, T. Staudt, G. P. Petrova, N. Tsud, T. Skála, A. Bruix, F. Illas, K.
C. Prince, V. Matolín, K. M. Neyman, J. Libuda, Nature Mater. 10, 310 (2011)
6. A. Bruix, Y. Lykhach, I. Matolínová, A. Neitzel, K. C. Prince, V. Potin, F. Illas, V. Matolín, J. Libuda, K.
M. Neyman, et al. Angew. Chem. Int. Ed. 53 (2014) 10525
7. H. A. Aleksandrov, K. M. Neyman, G. N. Vayssilov, Phys. Chem. Chem. Phys. 17 (2015) 14551
8. S. M. Kozlov, H. A. Aleksandrov, J. Goniakowski, K. M. Neyman, J. Chem. Phys. 139 (2013) 084701
9. S. M. Kozlov, H. A. Aleksandrov, K. M. Neyman, J. Phys. Chem. C 118 (2014) 15242
10. S. M. Kozlov, H. A. Aleksandrov, K. M. Neyman, J. Phys. Chem. C 119 (2015) 5180
11. S. M. Kozlov, G. Kovács, R. Ferrando, K. M. Neyman, Chem. Sci. 6 (2015), doi: 10.1039/c4sc03321c
12. G. Kovács, S. M. Kozlov, I. Matolínová, M. Vorokhta, V. Matolín, K. M. Neyman, Phys. Chem. Chem.
Phys. 17 (2015), doi: 10.1039/c5cp01070e
Gas-fed methanol fuel cell
Viktor Johánek, Anna Ostroverkh, Roman Fiala, and Vladimír Matolín
Department of Surface and Plasma Science, Charles University in Prague
V Holesovickach 2, 180 00 Prague 8, Czech Republic
Direct Methanol Fuel Cells (DMFCs) are typically operated with the fuel in its natural liquid form.
However, there is a trade-off between high fuel density requirement (to deliver maximum power) and
high fuel cell efficiency which drops at high methanol concentrations mainly due to the cross-over
through the proton exchange membrane (typically Nafion). To reduce this effect the fuel is fed as a
weak water solution.
Another possible approach is to supply the fuel in a gas phase which can be convenient not only
from the scientific standpoint but also for practical applications. In the rational development of fuel
cell catalysts the detailed information about the undergoing chemical processes is crucial. This
information can be accessed in a gas phase relatively easily (as compared to liquid) and in a very clean
and controllable manner. We used quadrupole mass spectrometry to analyze the composition of the
fuel cell "exhaust" directly during the cell operation under static load conditions. Main methanol
oxidation product at the anode (CO2) as well as possible by-products were monitored and correlated
with electrical quantities (voltage and current) measured simultaneously.
At FC anode, the methanol is oxidized into
carbon dioxide and six protons (as hydronium ions)
plus six electrons. The protons diffuse through the
membrane and react at the cathode with oxygen to
form water. Apart from CO2, other various surface
intermediates can be formed during methanol electrooxidation, mainly CO and CO-like species (COH,
HCO, HCOO, etc.) which are not readily oxidizable,
remain strongly adsorbed to the catalyst surface, and
thus can be the rate limiting step for the whole
Fig. 1: Current performance of a gas-fed
oxidation process or even deactivate the catalyst
DMFC with Pt anode and cathode at various
(temporarily or permanently).
methanol concentrations and voltage loads.
We examined and compared fuel cells with
commercial FC anode catalysts based on Pt and PtRh (Pt cathode in both cases) supported on a
standard carbon gas diffusion layer. It turns out that for a given load (FC voltage) there is a limit for
the methanol concentration in the supply stream under which the methanol conversion runs with very
high efficiency near 100%. Methanol over-feeding leads to significant loss of generated current and
time instabilities of the oxidation reaction, presumably due to the combination of cross-over effect and
temporary poisoning of the catalyst surface. The presence of Rh in the catalyst seems to contribute to
its better stability and higher resistance to excess methanol, at the expense of a slight reduction of FC
power performance.
From the practical point of view, gas-fed methanol FC proves to be more efficient solution than its
liquid-fed counterpart, mainly due to the reduced cross-over and higher level of operational control
(precise dosing with fast response time). Moreover, no fuel circulation or additional purification is
necessary to achieve high conversion rates.
Cheap precursor for synthesis of oxycarbide tungsten catalysts
N. Zanfoni, M. Giraudet, L. Imhoff, V. Potin, S. Bourgeois, B. Domenichini
Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), UMR 6303 CNRS – Univ.
Bourgogne Franche-Comté, 9 Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France,
Email: [email protected]
Tungsten carbonyl (W(CO)6) is the cheapest precursor of tungsten used for deposition of
metallic tungsten for instance in the field of microelectronic. However, the low reactivity of
such a precursor towards oxygen makes difficult its use in synthesis of oxide or oxycarbide
materials, even though it is well known that its decomposition under e-beam leads to oxides
containing a high amount of carbon. WF6 is also widely used but needs reductive agents (H2
or S2H6) which are hard to manage, in order to be deposed.
Hence, we have chosen an organotungsten precursor to perform deposition of a wide range of
oxycarbide materials. Especially, we focused on bis(cyclopentadienyl)tungsten(IV) dihydride
(Cp2WH2), which price is quite reasonable (180€ per gram). Playing on synthesis temperature
(fig.1) and oxygen flux, we have been able to obtain different tungsten oxycarbide thin films.
O1s
W4f
Intensity (a.u.)
C1s
600°C
500°C
400°C
1200
1000
800
600
400
200
0
Binding Energy (eV)
Fig. 1: XPS spectra of oxycarbides synthetized at 400, 500 and 600°C
Observation of porous Pt-CeO2 thin films directly grown on TEM grids
P. Simon, N. Zanfoni
Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB) - UMR 6303 CNRS-Univ. Bourgogne
Franche-Comté - 9 av. Alain Savary - 21078 Dijon Cedex- France
E mail: [email protected]
Transmission electron microscopy (TEM) is an essential tool for material characterization. However
when the sample is in form of a thin film, a careful and often time consuming preparation is required.
Furthermore the standard preparation techniques include mechanical and/or ion thinning steps which
are known to modify or damage the structure and chemical state of the samples. This is even more true
when the material is easily oxidized or reduced like cerium oxides, or when the substrate is fragile like
carbon material. In addition, the production of large electron transparent areas is not always obtained.
In the case of thin films obtained by direct liquid injection chemical vapor deposition, a new synthesis
approach has been considered which allows direct observations of the layers on TEM grids, requiring
no prior preparation of the deposits.
The carbon coated copper TEM grids are placed in the synthesis chamber and Pt-CeO2 nanolayers are
grown directly on the grids in a single step synthesis. Thus a very large electron transparent area is
obtained, since it’s the size of the grid (~29 mm²). In this way, the original chemical state and
morphology of the deposits are preserved and quantification of very low Pt content on large areas is
possible. High resolution (HR) measurements are also made very easy on the edge of the layers. TEM
images presented below show that the carbon membrane morphology is conserved. However, one
interesting fact is that the original carbon layer seems to disappear during deposition. Finally, due to
no additional protective layers deposited during preparation, this will probably make possible the
observation of single Pt atoms in surface nanopockets by HR scanning TEM.
Pt-CeO2 nanolayers deposited on TEM grids.
Modeling the structure and reactivity of ceria electrodes from ideal to realistic
reaction environments
Matteo Farnesi Camellone, Fabio Ribeiro Negreiros and Stefano Fabris
CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, National Research Council & SISSA, Trieste,
Italy
We combine DFT+U simulations with ab-initio molecular dynamics, metadynamics, and umbrella sampling
methods to provide insight into the new surface chemistry opened by novel non-conventional ceria catalyst with
ultra-low metal loading (1). The calculations are used to characterize the structure and the reactivity of the active
sites in a wide range of compositions and environments, from ideal surfaces to complex nano-structured catalysts
in the presence of liquid water at finite temperature.
We start with the hydroxylation and reduction of ceria surfaces driven by molecular H2, and demonstrate the sofar unrecognized entropic effects on the reaction mechanism and kinetics. Our metadynamics calculations show
that finite temperature effects alter the reaction mechanism, change the nature of the rate-limiting transition state,
and decrease the activation temperatures for H2 dissociation by more than 25% (2).
The study of supported sub-nm Pt clusters reveals that cluster morphology plays an important role in the
thermodynamics and kinetics of catalytically relevant surface processes such as cluster mobility, charge transfers
at the metal-oxide interface, reverse oxygen spillover, and oxygen vacancy formation (3,4).
We demonstrate the key role played by surface line defects on the dispersion and stabilization of specific Pt2+ and
Pt4+ species and investigate the different reactivity of these sites towards water, hydrogen and methanol oxidation
(5,6).
Finally, the distinct effects of liquid water, often present at realistic electrodes, on the surface chemistry of Ptceria catalysts are characterized on the basis of ab-initio molecular dynamics simulations (7).
(1)
www.chipcat.eu, Bruix et al, Angew. Chem. Int. Ed. 53, 10525 (2014).
(2)
Negreiros, F. R.; Farnesi Camellone, M.; and Fabris, S. submitted.
(3)
Ghosh, P.; Farnesi Camellone, M.; and Fabris, S. J. Phys. Chem. Lett., 2013, 4 (14), 2256–2263
(4)
Negreiros, F. R.; and Fabris, S. J. Phys. Chem. C, 2014, 118 (36), 21014–21020.
(5)
Szabova, L.; Tateyama, Y.; Matolin, V.; Fabris, S. J. Phys. Chem. C, 2015, 119 (5), 2537–2544.
(6)
Tran, N.-D.; Farnesi Camellone, M. and Fabris, S. submitted.
(7)
M. Farnesi Camellone, L. Szabova, V. Matolin, Y. Tateyama, and S. Fabris, submitted
IR Spectroelectrochemistry on Thin-Film and Model Fuel Cell Catalysts
O. Brummel, F. Waidhas, F. Faisal, R. Fiala1, M. Vorokhta1 I. Khalakhan1, Pohako-Esko2, P.
Wasserscheid2, V. Matolín1, J. Libuda
Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen,
Physical Chemistry II.
1
Charles University Prague, V Holešovičkách 747/2, 180 00 Praha 8, Surface Physics Group.
2
Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen,
Chemical Reaction Engineering.
Email: [email protected]
IR spectroelectrochemistry is a powerful method for in-situ studies on fuel cell catalysts. Here, we
present studies on Pt-doped CeO2 as a novel anode material as well as on Pt electrodes modified by
ionic liquids (IL).
We have investigated methanol oxidation in acidic solution on different Pt catalysts. Using the CO that
is formed during the reaction as a probe for the Pt surface sites, we compare Pt(111) electrodes, Pt
thin-film electrodes, and Pt-containing CeO2 thin-film electrodes with different Pt concentration. All
thin-film samples were prepared by magnetron sputtering and characterized by SEM, EDS and cyclic
voltammetry. Before measurement we cleaned the surfaces by potential cycling. On all samples, the
CO stretching frequency region is dominated by the on-top CO band between 2000 and 2100 cm-1. A
slight blue shift for the Pt thin-film in comparison to Pt(111) may be explained by co-adsorption of
electron withdrawing species, an increased CO density and earlier CO formation, due to the rougher
surface and higher reactivity (more pronounced s-shape of the CO band due to Stark shift.
For the Pt-doped CeO2 electrode with high Pt concentration two CO on-top peaks are identified which
are assigned to edges and terraces, respectively. The Pt-doped CeO2 electrode with the lower
concentration of Pt shows an extraordinary strong red shift. For both Pt concentrations we conclude
that a fraction of Pt2+ is reduced to Pt0 and stabilized in form of nanoparticles. Their size decreases
with decreasing Pt concentration. The strong red shift of at low Pt concentration indicates that the
presence of very small nanoparticles.
Regarding the modification of fuel cell catalysts with ILs, we investigated the adsorption of
[EMIM][OTf] on Pt(111) in the presents of water. To this end we analyzed the influence of the IL on
the COt signal for MeOH oxidation in acidic solution. Additionally, cyclic voltammetry was measured
as a function of the IL concentration, in the presence and in the absence of MeOH. We could identify
reversible and specific adsorption of the [OTf]- in a tilted geometry with increasing potential. For the
COt signal, a strong concentration-dependent redshift is observed in the presence of [EMIM][OTf].
This observation indicates a direct influence of the co-adsorbed IL on the CO-Pt bond.
TEM study of Pt alloys for fuel cells
Jaroslava Lavkova 1, 2, Martin Dubau 1, Mykhailo Vorokhta 1, Ivan Khalakhan 1,
Daniel Mazur 1, Iva Matolinova 1, Vladimir Matolin 1, Valerie Potin 2
1
Charles University, Department of Plasma and Surface Science, Prague
2
Laboratoire Interdisciplinaire Carnot de Bourgogne, Dijon
[email protected]
The interest in materials substituted for platinum for fuel cells (FC) applications is growing rapidly. A
full understanding of their workings as catalysts at a fundamental level presents a challenge to uncover
the microscopic pictures of their surface structure.
Our research is focused on both, anode and cathode side, such as extremely porous Pt-CeO2 structures
on nitrogenated amorphous carbon films (CNx) and PtCo layers, respectively. Their morphology and
crystallography was locally investigated by Transmission Electron Microscopy (TEM) technique.
Unfortunately, it is difficult to characterize individual oxide nanocrystals solely by experimental
methods. Thus, a combined methodology based on local crystallographic information and on computer
modelling is preferred. The shape of the cerium oxide crystals predicted by the Density Functional
Theory (DFT) – Fig. 1a [1] was confirmed by High Resolution TEM (HRTEM) images. The majority
of single-crystalline ceria nanoparticles with diameter of 2nm or larger are exposing {111} facets
truncated by {100} facets (Fig. 1b). Model studies determine {100} facets as stable position for Pt2+
anchoring and, thus, the high density of these favourable facets would explain high catalytic activity of
Pt-CeO2 nanoparticles [1]. Besides CeO2 crystals, the catalyst layer prepared on carbon substrate
contains also CeC2 particles [2] and Pt-Ce alloys as CePt2 and CePt5. Moreover, roughness and
porosity of the layers have a high influence on catalytic activity. Final shape of the structures is
dependent on deposition conditions, amount of deposited material and type of carbon substrate [3]. By
optimization and suitable combination of the materials the catalyst morphology can be tuned (Fig. 1c).
Nowadays, we focus our attention also to cathode side, particularly, to PtCo thin films [4]. The
preparation method by magnetron sputtering offers possibility to combine different compounds, with
low amount of noble metal on several substrates. The main progress was done in the morphology
study: from continuous layers on flat substrate, through GLAD deposited layers to porous structures
on commercial nanoGDL substrate (Fig. 1d) and on nanoGDL upgraded by CNx intermediate layer for
better stability of the system. Unfortunately, it is not possible to reveal the crystallography from
HRTEM micrographs unambiguously, as the lattice constant for metallic Pt is very closed to the PtCo
alloy. However, in same cases, we can confirm the observation of several metallic Pt nanocrystals in
the layer (Fig. 1e), as the measured distances and angles correspond just to the zone axis of platinum.
Such prepared thin films can be used as catalyst and by suitable combination of deposition parameters
and materials we are able to create promising constructions for fuel cell applications.
Figure 1: ANODE SIDE: DFT model of CeO2 particle and Pt anchoring [1] (a), CeO2 [101] nanocrystal (b), PtCeO2 layer on CNx (c). CATHODE SIDE: Pt-Co layer on nanoGDL (d), Pt [001] nanocrystal (e).
[1] A. Bruix et al. Angewandte Comm. 53 (2014) 10525-10530
[2] J. Lavkova et al. Nanoscale 7 (2015) 4038-4047
[3] M. Dubau et al. ACS Appl. Mater. Interfaces 6, (2014) 1213-1218
[4] R. Fiala et al. J. Power Sources, 273 (2015) 105-109
PtCeO2 on CNx as a anode for PEMFC
Roman Fiala, Martin Dubau, Tomáš Duchoň, Marie Aulická, Michal Václavů,
Vladimír Matolín
Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science,
V Holešovičkách 2, 18000 Prague, Czech Republic
E mail: [email protected]
In recent decades lots of studies introducing the hydrogen as an energy carrier for near future are
appeared. For this hydrogen-energy conversion is crucial the proton exchange membrane fuel cell
PEMFC. The most effective commercial widely used catalyst for PEMFC is platinum, which is nobble
metal so it is important reduce amount of it.
The one way is find out another platinum free catalyst. The promising way is reduced amount of
platinum by platinum doped cerium oxide film prepared by magnetron sputtering. It was shown that
such a catalyst exhibited comparable power density in comparison with commercial Pt catalyst while
the specific power per gram of platinum is hundred times higher[1-4].
Another problem is stability of catalyst because the common support for catalyst layer is carbon which
corrodes. This carbon corrosion could be diminished using CNx support layer instead of carbon
powder.
In this work is presented comparison between fuel cell performances with PtCeO2 on regular carbon
gas diffusion layer coated by carbon nanoparticles (nGDL) with fuel cell performance using PtCeO2
on nGDL pre-coated by NCx layer. These films were investigated using photoelectron spectroscopy
(XPS), Energy-dispersive X-ray spectroscopy (EDX) and the morphology was characterized by
secondary electron microscopy SEM.
[1] Fiala, R; Vaclavu, M; Vorokhta, M; Khalakhan, I; Lavkova, J; Potin, V; Matolinova, I; Matolin,
V¨, J. Power Sources, 273 (Jan): 105–109, 2015.
[2] Fiala, R; Vaclavu, M; Rednyk, A; Khalakhan, I; Vorokhta, M; Lavkova, J; Potin, V; Matolinova, I;
Matolin, V, Catal. Today, 240 Part B (1 Feb): 236–241, 2015.
[3] Fiala, R; Khalakhan, I; Matolinova, I; Vaclavu, M; Vorokhta, M; Sofer, Z; Huber, S; Potin, V;
Matolin, V, J. Nanosci. Nanotechnol., 11 (6): 5062–5067, 2011.
[4] Matolin, V; Matolinova, I; Vaclavu, M; Khalakhan, I; Vorokhta, M; Fiala, R; Pis, I; Sofer, Z;
Poltierova-Vejpravova, J; Mori, T; Potin, V; Yoshikawa, H; Ueda, S; Kobayashi, K,
Langmuir, 26 (15): 12824–12831, 2010.
Tuning the ORR electrocatalytic properties via Pt hollow nanostructures
L. Dubau, 1, 2, * R. Chattot, 1, 2 T. Asset, 1, 2 and F. Maillard 1, 2
1 Univ. Grenoble Alpes, LEPMI, F-38000 Grenoble, France; 2 CNRS, LEPMI, F-38000 Grenoble, France
* [email protected]
The ever-growing energy demand worldwide and the announced end of the so-called “fossil fuel era” are currently
boosting the development of electrochemical energy technologies, such as fuel cells, batteries and supercapacitors. In
proton-exchange membrane fuel cells (PEMFC), special effort has been paid to improve the catalytic activity for the
oxygen reduction reaction (ORR) of the cathodic material, its stability and to decrease its precious metal content.
This study describes the advantages of hollow nanostructures composed of a Pt-rich outer-layer surrounding a central
void. Pt-rich hollow nanoparticles with different Pt-shell thicknesses were synthesized via a method involving the
galvanic replacement of Ni atoms by Pt atoms, and the nanoscale Kirkendall effect. Increasing the Pt:Ni stoichiometry
from 1:1 to 1:5 in the initial metal precursor solution resulted into a thinner Pt-rich shell and an increased Pt lattice
contraction (Figure 1). The most promising electrocatalyst achieved 6-fold and 10-fold enhancement in mass and
specific activity for the ORR, respectively over standard solid Pt/C nanocrystallites of the same size. This
enhancement was ascribed to (i) their opened porous architecture, (ii) their preferential crystallographic orientation
(“ensemble effect”), and (iii) the weakened oxygen binding energy induced by the contracted Pt-Pt distance (“strain
effect”). The stability of the hollow nanostructure was investigated by high temperature X-ray diffraction, identicallocation transmission electron microscopy, and correlated to changes in catalytic activity.
Figure. 1 : Specific activity determined from the steady-state I–E curves at  = 1600 rpm. O2-saturated 0.1 M HClO4;
potential sweep rate v = 0.005 V s−1; positive-going potential sweep from E = 0.4 to 1.0 V vs RHE; T = 298 ± 1 K.
The currents are normalized to the real surface area estimated by COad stripping coulometry.
1. L. Dubau, M. Lopez-Haro, J. Durst, L. Guétaz, P. Bayle-Guillemaud, M. Chatenet, F. Maillard, J. Mater. Chem. A. 2, 1849718507 (2014).
2. L. Dubau, T. Asset, C. Bonnaud, R. Chattot, V. van Peene, F. Maillard, submitted.
This work was performed within the framework of the Centre of Excellence of Multifunctional Architectured
Materials "CEMAM" n° AN-10-LABX-44-01 funded by the "Investments for the Future" program. The authors
acknowledge financial support from University of Grenoble-Alpes through the AGIR program (grant # LL1492017G),
and from the French national Research Agency through the HOLLOW project (grant # ANR-14-CE05-0003-01).
Tuning Pt Catalysts for Fuel Cells by Metal-Oxide Interactions
Sergey M. Kozlov1 and Konstantin M. Neyman1,2
1
Departament de Química Física & Institut de Química Teòrica i Computacional,
Universitat de Barcelona, Barcelona, Spain
2
Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
Email; [email protected]
Metal-oxide interactions allow going beyond limited diversity of properties of transition metals to
devise novel catalysts. In particular, exploiting synergy between Pt nanoparticles and ceria support one may
create highly stable and active catalysts for fuel cell applications. However, atomistic details of metal-oxide
interactions, in general, and Pt-ceria interactions, in particular, remain poorly understood.
In the present work we investigate using density functional theory methods how ceria modifies charge
state, electronic and geometric structure of supported ~1.5 nm large Pt nanoparticles. We find that Pt
nanoparticles may donate several electrons to ceria reducing certain Ce4+ cations to Ce3+, which affects
density of states of Pt atoms on the interface with the support [1]. To put Pt-ceria interactions into
perspective we compare them to interactions between Pt nanoparticles and MgO(100) support [2-4], which is
commonly considered to be chemically inert.
This work is a touchstone electronic structure study of electronic metal-support interactions involving
1.5 nm large nanoparticles representative of larger species commonly found in catalytic experiments and
applications. It sheds light on fundamental aspects of metal-oxide interfaces that have practical implications
for Pt-ceria fuel cell catalysts.
1. Y. Lykhach, S.M. Kozlov, V. Matolín, K.M. Neyman, J. Libuda et al., submitted
2. S. M. Kozlov, H. A. Aleksandrov, J. Goniakowski, K. M. Neyman, J. Chem. Phys. 139 (2013) 084701
3. S. M. Kozlov, H. A. Aleksandrov, K. M. Neyman, J. Phys. Chem. C 118 (2014) 15242
4. S. M. Kozlov, H. A. Aleksandrov, K. M. Neyman, J. Phys. Chem. C 119 (2015) 5180
Structure and reactivity of the electrode/water interface
from ab-initio molecular dynamics simulations
Matteo Farnesi Camellone and Stefano Fabris
CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, National Research Council & SISSA, Trieste,
Italy
Email: [email protected]
The interface that forms between a metal-oxide surface and an aqueous solution creates a unique reaction
environment that can strongly influence the reactivity of molecules at the interfacial region. The metaloxide/aqueous interface offers a unique reaction environment for molecules other than H2O, by providing a
reaction center and environment that combines features that are important for both homogeneous and
heterogeneous catalyzed reactions. Reducible oxides represent very active catalytic supports, and among them,
ceria (CeO2) is one of the most efficient due to its oxygen storage capacity. Understanding the interaction
between water and CeO2(111) surfaces is crucial in many catalytic applications. Water is impossible to exclude
from realistic environments; thus, knowledge of its behavior on ceria surfaces is important. Moreover, the waterceria interface is central in many technological applications, such as fuel cell electrodes, artificial photosynthesis
or in hydrogen production/purification.
We use ab initio DFT+U molecular dynamics to study the complex interface of CeO2 and water. The ab initio
simulations uncover the microscopic details of solvent-induced proton hopping at the water/oxide interface (1).
We show how hydrogen bonding and hydrogen bond fluctuations at the water/oxide contact are responsible for
the change in the structure and proton transfer dynamics. Finally we discuss some preliminary results on largescale AIMD simulations aimed to investigate solvent effects at a platinum nanocluster grown on a CeO2 surface
being in contact with liquid water (2).
(1)
M. Farnesi Camellone, L. Szabova, V. Matolin, Y. Tateyama, and S. Fabris, submitted
(2)
L. Szabova, M. Farnesi Camellone, V. Matolin, Y. Tateyama, and S. Fabris, in preparation.
Modelling interactions of transition metal species with ceria nanoparticles
for applications in fuel cell catalysts
Alberto Figueroba,1 Albert Bruix,2 Gábor Kovács1 and Konstantin M. Neyman1,3
1
Departament de Química Física & Institut de Química Teòrica i Computacional, Universitat de
Barcelona, Barcelona, Spain
2
Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, Aarhus
University, DK-8000 Aarhus C, Denmark
3
Institució Catalana de Recerca I Estudis Avançats (ICREA), Barcelona, Spain
Email: [email protected]
Platinum is one of the most versatile elements in catalysis. Nevertheless, the very high market
price hinders many of its large-scale applications. There are two main avenues to reduce the amount of
this precious metal in catalysts while keeping the efficiency of the latter. The most challenging
approach is to completely substitute Pt by other less expensive metals or alloys. The other option is to
increase the number of active surface sites of Pt available for reactants for a smaller amount of Pt.
Single Pt atoms dispersed on {100} nanofacets of ceria particles have been recently shown to be
exceptionally stable, being able to resist agglomeration and material degradation processes up to 700
K [1].
In the present work we studied the stability of other eleven late transition metal atoms adsorbed on
the {100} nanofacets of ceria particles. The interaction with the oxide support drives the oxidation of
the metal atoms with the concomitant reduction of Ce4+ cations to Ce3+. In all cases, this adsorption is
found to be more stable than the formation of metal aggregates [2]. The substitution of a cerium atom
by a transition metal atom (doping by Pt, Pd or Ni) in different positions of the nanoparticle has also
been analysed. The diffusion of the dopants from their inner positions to the surface is calculated to be
driven energetically and accompanied with the release of an oxygen atom of ceria.
To assist in the reliable experimental characterization of Pt species, a technique for calculating the
EPt4f binding energies has been developed. This approach allows one a direct comparison of the
calculated core-level shifts with the values measured by the X-ray photoemission spectroscopy.
1. A. Bruix, V. Matolín, J. Libuda, K.M. Neyman et al. Angew. Chem. Int. Ed. 53 (2014) 10525
2. A. Figueroba, G. Kovács, A. Bruix, K. M. Neyman, in preparation
Mechanisms of High Temperature PEM Fuel Cell Catalyst
Electrochemically Active Surface Area Deterioration
Dr. Tomas Bystron
University of Chemistry and Technology Prague
High temperature fuel cells with proton exchange membrane (HT PEM FC) attract a lot of attention as
convertors of chemical energy of H2-O2 couple to electrical energy. Operating temperature of
150-200 °C offers lot of benefits from the operational point of view. On the other hand it restricts the
type of applicable membranes to these based on polybenzimidazole doped with H3PO4. A
combination of such media and elevated temperature represents environment with enhanced
degradation aggressivity.
Several following mechanisms of HT PEM FC degradation, all of which lead to decrease of
electrochemically active surface area (EASA), can be distinguished. Amongst most important can be
mentioned: mechanical damage of the gas diffusion electrode/layer; carbon support (electro)chemical
oxidation; Pt nanoparticle coarsening due to their surface diffusion, coalescence and sintering; Pt
dissolution to Pt2+ ions and their redeposition on larger particles with lower surface energy (Ostwald
ripening). Extent of the individual processes depends on the operational conditions.
Another aspect to be considered is FC “self” poisoning of the Pt catalyst by phosphorus compounds.
These are generated on the anode during FC operation by reducing H3PO4. Most important of these
compounds were shown to be H3PO3 and elemental phosphorus which are strongly adsorbed on the Pt
surface.
The aim of our work was to study mechanisms of EASA decrease in HT PEM FC. We focused mainly
on the effect of operational conditions on the Pt catalyst particle coarsening and determination of
H3PO3 electrochemical behaviour on the Pt electrode.
Second Generation graphene for a rational design of Advanced Functional
Architectures for Energetics
M. Favaro, M. Cattelan, S. Agnoli and G. Granozzi
Department of Chemical Sciences, University of Padova, Italy
Email: [email protected]
Graphene is an extremely intriguing material that is arousing a formidable amount of interest in many
different disciplines. Nowadays, the focus of scientists' attention has moved towards more complex systems
like chemically modified graphene (CMG) and 3D systems based on the assembly of graphene sheets. 1
However, despite many successful applications and the synthesis of very different materials, a basic
understanding of the phenomena taking place at the atomic level is still missing, as is a clear correlation
between structure and properties. Surface science, by virtue of its reductionist approach, can certainly make
an important contribution to these new branches of research. Graphene has also proved to be an effective
and versatile support for electroctalysis or an electrocatalyst itself when doped with heteroatoms.
In the present talk the activity of the Surface Science and Catalysis group of the University of Padova in the
field of CMGs will be summarized, with particular focus on their use as electrocatalysts. In particular,
single- and multi-doped graphene oxide quantum dots will be discussed with respect to their activity toward
Oxygen Reduction Reaction. They have been synthesized by a simple electrochemical method using water as
solvent, obtaining different singly doped (Boron, Nitrogen, Sulfur) and dually doped (B,N-, S,N-) graphene
oxide quantum dots.2,3 The chemical composition and structural properties of the obtained materials has been
characterized by photoemission and near edge X-ray absorption spectroscopy, and scanning tunnelling
microscopy. The electrochemical activity toward the oxygen reduction reaction of the doped graphene oxide
quantum dots has been investigated by cyclic voltammetry and rotating disk electrode measurements. The
body of our experimental data demonstrates that the selectivity of the oxygen reduction reaction is controlled
by the oxidation degree of the materials: as-prepared graphene oxide quantum dots, which present highly
oxidized functional groups, follow a two-electron reduction pathway and produce hydrogen peroxide,
whereas after a reduction treatment by NaBH4, the same materials favor a four-electron reduction of oxygen
to water. The high selectivity and high efficiency of the as-prepared graphene oxide quantum dots toward the
production of hydrogen peroxide can be successfully exploited for water remediation applications.
1
S. Agnoli and G. Granozzi, Surf. Sci., 2013, 609, 1-5.
2
M. Favaro, L. Ferrighi, G. Fazio, L. Colazzo, C. Di Valentin, C. Durante, F. Sedona, A. Gennaro, S. Agnoli
and Gaetano Granozzi, ACS Catalysis, 2015, 5, 129-144.
3
M. Favaro, M. Cattelan, F. Carraro, L. Colazzo, C. Durante, M. Sambi, A. Gennaro, S. Agnoli and G.
Granozzi, J. Mat. Chem. A, in press.
In-situ electrochemical atomic force microscopy study of the evolution of
Pt-Ni and Pt-Co thin film ORR catalyst during electrochemical aging test
Ivan Khalakhan
Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma
Science, V Holešovičkách 2, 18000 Prague, Czech Republic
Pt-Co and Pt-Ni thin film catalysts were prepared by using simultaneous magnetron sputtering
of Pt and Co/Ni and showed high activity on a cathode side of a proton exchange membrane
fuel cell (PEMFC).
By combining for the first time in situ electrochemical atomic force microscopy (EC-AFM)
technique with ex-situ energy dispersive X-ray spectroscopy (EDX) and photoelectron
spectroscopies (XPS and SRPES) we accelerate electrochemical aging test and have shown
that thin film catalysts transform under electrochemical aging test, forming Pt skin layer due
to Co/Ni leaching.
The similar transformation process was proved to occur in real membrane electrode assembly
of the fuel cell.
Atomically dispersed and tin-doped noble metal model catalysts: preparation,
stability, reactivity
Yaroslava Lykhach,1 Armin Neitzel,1 Tomáš Skála,2 Mykhailo Vorokhta,2 Nataliya Tsud,2
Sascha Mehl,1 Klára Ševčíková,2 Kevin C. Prince,3 Vladimír Matolín,2 Jörg Libuda1,
1
Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany; 2Charles University,
Prague, Czech Republic; 3Elettra-Sincrotrone Trieste SCpA, Italy
E mail: [email protected]
Fuel Cells are considered the next generation power sources for portable and stationary applications.
Platinum is an essential catalytic element of both the anode and cathode electrodes. The high cost of
platinum is the main factor limiting large-scale application of fuel cell technology. Principle strategies to
resolve this challenge involve either the replacement of the noble metal or a more efficient use of the
precious material. The latter is achieved by maintaining a very high dispersion of noble metal during
operation. The ultimate noble metal efficiency can be achieved upon atomic dispersion of noble metal on
the surface of nanostructured cerium oxide [1].
In the present study we employed a model approach to investigate the stability and the reactivity of Pt2+
sites anchored at the surface of CeO2 films. The model Pt-CeO2 films were prepared under wellcontrolled conditions by means of co-deposition of Pt and Ce in an oxygen atmosphere. We found that
hydrogen dissociation occurs exclusively in the presence of metallic Pt 0. Under these circumstances, the
catalytic activity and high stability of Pt-CeO2 were maintained due to a redox switching between Pt2+ and
Pt0 states. Following this approach we tested different metals (Pd and Ni) that can potentially substitute Pt.
We found, that unlike Ni-CeO2, Pd-CeO2 exhibits similar properties to Pt-CeO2 including facile redox
switching between Pd2+ and Pd0 states.
In the next step, the redox functionality of atomically dispersed catalysts can be improved by adding Sn.
We found that Sn triggers the reduction of Pt2+ even at 300 K. In particular, the reduction of Pt2+ upon
reaction with hydrogen is coupled with the reduction of Sn followed by likely formation of Pt-Sn alloy
particles on Sn-Pt-CeO2.
[1] Bruix, A.; Lykhach, Y.; Matolínová, I.; Neitzel, A.; Skála, T.; Tsud, N.; Vorokhta, M.; Stetsovych, V.;
Ševčiková, K.; Mysliveček, J.; Fiala, R.; Václavů, M.; Prince, K. C.; Bruyere, S.; Potin, V.; Illas, F.;
Matolín, V.; Libuda, J.; Neyman, K. M., Angew. Chem., Int. Ed., 53, 10525, (2014).
Noble metals in heterogeneous catalysis: down to zero
Eric Marceau
Laboratoire de Réactivité de Surface, UMR 7197 CNRS, UPMC, Site d’Ivry, 94200, Ivry-surSeine, France.
Email : [email protected]
Since its first developments at the onset of the 19th century, heterogeneous catalysis has
heavily relied on noble metals, in particular platinum and palladium, more recently rhodium, gold and
silver. However, because their natural abundance is low and and their distribution on Earth is most
uneven, these metals were, and still are, critical materials with respect to their cost and availablity. For
instance, the price of palladium has been seen to constantly rise in the last ten years, suggesting that a
« palladium peak », similar to the « oil peak », has been passed.
Noble metals in heterogeneous catalysis are used in large-scale industrial processes,
depollution devices or for the transformation of platform molecules. In the domain of catalytic
hydrogenations, several strategies are currently implemented to address the expected price rise and
possible shortage of noble metals. This presentation will focus on several of them : isolating noble
metal sites on a support, or diluting them on base metals, in order to decrease their loading ; replacing
them by base metals such as nickel, or by an association of base metals, with specific issues linked to
the control of the base metals dispersion ; preparing other types of catalytic phases involving metals
and elements from the p-block. Very recent developments suggest that catalytic hydrogenation on
metal-free solid systems, such as defective hexagonal boron nitride, may also be possible.
Sputtered Platinum-Cobalt Oxygen Reduction Reaction Catalyst
Michal Vaclavu, Roman Fiala, Mykhailo Vorokhta, Ivan Khalakhan, Iva Matolinova and
Vladimir Matolin
Charles University in Prague, Faculty of Mathematics and Physics, Prague, Czech
Republic
Fuel cells (FC) are considered as key future alternative energy sources. In the effort to
develop planar technology compatible fuel cell device it is essential to validate and develop thin
film technology prepared catalyst.
It this report we want to present results obtained from platinum-cobalt based catalyst
prepared by magnetrone sputtering. Its activity and performance for oxygen reduction reaction
(ORR) on the cathode of hydrogen proton exchange membrane fuel cell (PEMFC) is evaluated.
We tried to optimize the ratio of Pt versus Co in the catalyst layer and also the equivalent loading
of the catalyst in respect to performance in terms of specific power and mass activity.
We show that in ideal case the catalyst offer good mass activity and specific power up to 5
W.mg-1(Pt) which is significantly better than compared to commercially available cathode
catalyst.
Central-European Research Infrastructure Consortium – distributed research
facility for multitechnique materials research
Daniel Mazur
CERIC-ERIC, c/o Elettra Sincrotrone Trieste, loc. Basovizza, Italy
Surface Physics Laboratory, Charles University in Prague, Czech Republic
E mail: [email protected]
In 2014 a distributed research facility CERIC-ERIC for materials research was created to provide simplified, yet
open and peer-reviewed user access for proposals requiring multitechnique diagnoses unavailable in one single
location.
Apart from the Surface Science Laboratory in Prague and its auxiliary Materials Science beamline (Elettra
synchrotron in Trieste, Italy) dedicating photoelectron spectroscopies and scanning electron microscopy, the
CERIC-ERIC provides user access to several other Elettra synchrotron beamlines, small-angle x-ray scattering
facilities, nuclear magnetic resonance facilities, high-resolution transmission electron microscope, MeV-ion
tandem accelerator beamlines and thermal neutron beamline instruments.
Distributed across seven European countries and still growing, the research infrastructure is serving an increasing
number of international users in regular calls every 6 months. Simultaneously, CERIC-ERIC is implementing
measures to integrate the heterogeneous experimental facilities, extend user support of all facilities and promote
the multidisciplinary skills in the research community of advanced nanomaterials.
Using synchrotron radiation for in-situ structural investigations
of model electrochemical interfaces
Jakub Drnec
European Synchrotron Radiation Facility
BP 220, F-38043 Grenoble Cedex
Email: [email protected]
The hard x-ray radiation is one of the few available probes that can be used to study buried interfaces
owing to its large penetration depth. This also makes it an ideal tool for in-situ and in-operando
investigations of electrochemical liquid-solid interfaces, giving an unprecedented insight into the
structure, morphology, and electronic properties of materials during operation of electrochemical
devices.
In this presentation, I will introduce a few examples of how the hard x-ray probe can be used in
electrochemistry and what kind of information can be obtained. In the first part, I will focus on the
investigation of Zn and Ni electrodeposition on Pt single crystal surfaces which are systems of interest
for Oxygen Reduction Reaction (ORR) catalysis.
The second part of the talk will be devoted to electrochemical Pt oxidation, a process of great
importance for stability and activity of Pt catalysts in fuel cells. In particular, the influence of the
presence of oxygen during ORR on the oxidation behaviour will be discussed.
Finally, I will give an example of an in-situ study of Pt-CeO2 fuel cell catalyst and reasons of its
interesting performance.
Approach and main steps of microfabrication
Massimo Tormen
ThunderNIL srl, c/o CNR-IOM Lab. Tasc, Area Science Park , SS14 km163,5
Basovizza, 34149 Trieste, Italy
Email: [email protected]
Mass spectrometry of fuel cell exhaust
A. Ostroverkh, V. Johánek, R. Fiala, V. Matolín
Dept. Surface and Plasma Science, Charles University in Prague,Czech Republic
e-mail: [email protected]
In direct alcohol fuel cells small organic molecules, such as methanol or ethanol convert chemical energy to
electrical energy. These promise to be an efficient means use as fuels without first reforming them to
hydrogen gas. But to become practical, there are materials related troubles which must first be overcome.
Improving the kinetics of fuel electrooxidation at the anode is a major goal. In order to gain mechanistic
insights into this reaction and guide the search for new catalysts, we use quadrupole mass-spectrometry
techniques.
Chemical species generated at a catalyst can be detected with mass-spectrometry technique with very little
time delay. As an example, figure shows the efficiency of DMFC at a PtRu catalyst, and the simultaneously
recorded signals for CO2 and current. Time of delay is 110sec. Inset shows all exhaust products of DMFC.
H2 activation on atomically dispersed and nanoparticular noble metal
catalysts
Armin Neitzel, Yaroslava Lykhach, Jörg Libuda
Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Erlangen, Germany; Viktor
Johánek, Mykhailo Vorokhta, Tomáš Skála, Nataliya Tsud, Vladimír Matolín;
Department of Surface and Plasma Science, Charles University, Prague, Czech Republic;
Kevin Charles Prince;
Sincrotrone Trieste SCpA and IOM, Trieste, Italy
Email: [email protected]
Hydrogen Fuel Cells attract significant attention as environmentally friendly power sources for a
variety of applications ranging from the automotive vehicle propulsion to the chip-integrated microdevices. Hydrogen activation is an essential step in the production of electricity in the FC.
In the present study, we investigated H2 activation on Pt-CeO2 mixed oxides as a function of the Pt
content by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission
spectroscopy. Pt-CeO2 mixed oxides were prepared by co-deposition of metallic Pt and Ce in an
oxygen atmosphere on well-ordered CeO2(111) buffer layers on Cu(111) at 110 K followed by brief
annealing at 700 K. Following this preparation procedure, we prepared samples containing
exclusively Pt2+ (5% Pt-CeO2) and Pt2+ in combination with Pt0 in the form of small particles (15-18%
Pt-CeO2). According to our previous study [1], Pt2+ ions are stabilized at (100) nanofacets at the
surface of nanostructured CeO2 films.
H2 dissociation occurs only in the presence of metallic Pt0 on the 15% and 18% Pt-CeO2 substrates.
Below 300 K, H2 activation yields hydroxyl groups which prevent hydrogen spillover from Pt to the
substrate. Above 350 K, reduction of Pt2+ is accompanied by the formation of oxygen vacancies due
to the reaction of hydrogen with oxygen provided by the reverse oxygen spillover from the substrate
to the Pt particles.
In contrast, CH3OH dissociation appears to be not influenced by the presence of Pt2+ or metallic Pt.
Annealing in methanol atmosphere above 450 K leads to a strong reduction of Ce4+ and Pt2+ in the PtCeO2 mixed oxides. Interestingly, the reduction of Pt2+ upon reaction with methanol does not require
the presence of metallic Pt.
[1] A. Bruix, Y. Lykhach, I. Matolinova, A. Neitzel, T. Skala, N. Tsud, M. Vorokhta, V. Stetsovych,
K. Sevcikova, J. Myslivecek, R. Fiala, M. Vaclavu, K.C. Prince, S. Bruyere, V. Potin, F. Illas, V.
Matolin, J. Libuda, K.M. Neyman, Angew. Chem. Int. Ed. Engl 53, 10525 (2014)
Development of transition metal carbide thin films
for proton exchange membrane fuel cells
J. Nazon, M. Herbst, M.C. Marco de Lucas, S. Bourgeois, B. Domenichini
Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS – Univ. Bourgogne
Franche-Comté, 9 avenue Alain Savary, BP 47870, F-21078 DIJON Cedex, France
Email : [email protected]
Significant progress has taken place over the past decades in understanding catalysis in electrochemical systems.
In proton exchange membrane fuel cells (PEMFCs) a very important issue is the use of highly active and high
surface area electrocatalysts. Platinum-based material are the most common commercial ones. However the cost
of Pt and the limited world supply are significant barriers for large-scale production of fuel cells. So, significant
reductions of Pt loadings should be achieved. One of the approaches includes the use of Pt-free catalysts. Among
the potential candidates, transition metal carbide (MC) appears to be attractive. In addition to its high thermal
stability and chemical inertness, MC presents platinum like catalyst behavior. However, little research has been
conducted on the use of transition MC catalyst in PEMFCs. Transition metal carbide can be prepared by many
methods, but the key issue in synthesis is the difficulty to produce MC films with high surface area.
This work focuses on the synthesis of highly porous MC (M = W, Ce) films by radio-frequency reactive
sputtering and has to be considered as the first step in developing Pt free catalyst and its integration in PEMFC
technology. For this purpose, a PVD chamber was developed coupled to X-ray Photoelectron spectroscopy
system in order to achieve in-situ elaboration/characterization of transition MC films. The effect of three
processing parameters on the chemical and microstructural properties of transition metal carbide films was
investigated. The evolution of the chemical composition at the material surface was analyzed by photoemission
whereas the change in nanostructure was studied through electron microscopy techniques. The evolution of
metal content in the thin films was correlated to the crystalline structure, investigated by X-ray diffraction and
Raman spectrometry.
This study evidenced the major role of methane to argon gas flow ratio as well as the power applied to the
metal target. The chemical composition of the films is indeed easily controlled by playing with the methane
flow rate and with the power. In the case of WC films, the surface tungsten content in the film varies from
0.02 to 0.8 with the change of these two parameters. The homogeneity of tungsten content in the whole film
was confirmed by EDS analyses. By means of photoemission, XRD and Raman spectroscopy analyses,
tungsten carbide films seems to be mainly composed of cubic substoichiometric WC1-x phase. Concerning
the cerium carbide, films seem to be mainly composed of Ce1-xCx phase embedded in amorphous carbon. The
investigations will be continued for reducing the carbon content in the films.
Carbide layers are found to exhibit dense columnar growth perpendicular to the substrate surface whatever
the processing parameters are. The film surfaces have a cauliflower shaped microstructure which is related to
the columnar growth and associated with intercolumn voids. In order to increase the porosity of the films,
GLancing Angle Deposition was used. Porous films consisting of spaced columns are demonstrated by using
this technique. The morphology of the columns could be controlled by changing the substrate angular
frequency and substrate position relative to sputtered particle source.
PEM water electrolysis in context of H2 economy
Peter Kúš, Roman Fiala, Michal Václavů, Mykhailo Vorokhta, Vladimír Matolín
Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma
Science, V Holešovičkách 2, 18000 Prague, Czech Republic
Modern world is increasingly leaning towards using renewable sources for power generation. Power
generated in this manner (e.g. harvested from solar or wind energy) is however volatile in nature and in
order to be used efficiently, requires incorporating certain buffer within the electrical grid.
PEM electrolyzer for decomposition of water during power overproduction and subsequent usage of
hydrogen as a fuel for fuel cells in time of power shortage, is an ideal candidate for such application. Since
common catalyzers for water electrolysis differ from those for hydrogen fuel cells, above mentioned
system would need to consist of two dedicated devices.
We present the idea and preliminary results of Pt-Ir magnetron sputtered bimetal catalyst which can be
used for water decomposition / oxygen evolution reaction (OER) in PEM water electrolyzer and at the
same time for oxygen reduction reaction (ORR) in hydrogen fuel cell. As a consequence Pt-Ir could be
used in single regenerative fuel cell in order to simplify the buffer cycle design.
Optimization of Electron Beam Lithography Process for Fuel Cell Patterning
Sarka Chlupova, Iva Matolinova
Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science,
V Holešovičkách 2, 18000 Prague, Czech Republic
Email: [email protected]
We present the results of the optimization of the electron beam lithography process for applying of functional
coatings (electrodes and catalysts) proposed design for planar micro-fuel cells. The main objective of this
work was to find parameters which were fit for the preparation of a suitable resist mask on the structured
silicon surface. Optimization of process parameters as a thickness of the resist layer, a radiation dose and
exposition time which allow the selective resist removal by immersing it in solvent during resist developing
was performed on plane silicon surfaces.
Then appropriate parameters have been applied on silicon structured with the micro-channels on the surface.
Cross-linked polymethylmethacrylate (PMMA) of two different molecular weights diluted in anisole was
used as a negative resist material. The polymer resists were spread by the spin-coating method. The rotation
speed during spin-coating was adjusted to get the appropriate thickness of the resist layer, which was
controlled with the Atomic Force Microscope (AFM).
EBL exposure of the resist-coated sample was carried out using a dedicated DrawBeam software module
directly in the scanning electron microscope (SEM) chamber at 30 keV electron beam energy. The
optimization of the exposure dose aimed to creation of a line in the polymer mask of the thickness
corresponded to the distance between the two micro-channels. In final phase of the electron beam
lithography procedure the deposition of a functional layer to the canals on the silicon wafer through the
polymer mask was performed. The process was completed by ultrasonically assisted lift-off in acetone. It
resulted in the removal of the polymer mask covered with the functional layer, and only the planar channels
remain filled with the active layer.
Surface Composition of Magnetron Sputtered Pt-Co Thin Film Catalyst for
Proton Exchange Membrane Fuel Cells.
Mykhailo Vorokhta 1*, Michal Václavů1, Ivan Khalakhan1, Roman Fiala1, Peter Kúš1, Tomaš
Skála1, Natalia Tsud1, Jaroslava Lavková1, Valerie Potin2, Iva Matolínová1, Gabor. Kovács,3
Sergey. M. Kozlov,3 Konstantin. M. Neyman,3,4 Vladimir Matolín1
1
Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma
Science, V Holešovičkách 2, 18000 Prague, Czech Republic
2
Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de
Bourgogne, 9 Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France.
3
Departament de Química Física and Institut de Química Teòrica i Computacional
(IQTCUB), Universitat de Barcelona, c/ Martí i Franquès 1, 08028 Barcelona, Spain
4
Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
*Email: [email protected]
The substitution of Pt by Pt-Co in proton exchange membrane fuel cell is a way to increase cost
effectiveness of the latter. In this work we have studied the magnetron sputtered Pt-Co thin film
catalyst, by using both experimental and theoretical methods.
Testing this catalyst in a hydrogen-fed proton exchange membrane fuel cell showed high catalytic
activity for oxygen reduction reaction. Scanning electron microscopy and transmission electron
microscopy experiments confirmed the nanostructured character of the catalyst. By using surface
analysis techniques, such as synchrotron radiation photoelectron spectroscopy, X-ray photoelectron
spectroscopy and near edge X-ray adsorption spectroscopy, the surface composition of as-deposited
and annealed at 773K Pt-Co films was investigated. It is demonstrated that the annealing stabilize the
catalyst at the state with the Pt-rich surface.
The theoretical modeling based on density functional theory shows that platinum tends to segregate on
the surface forming a Pt-rich shell in nanostructured Pt-Co in agreement with experimental data. It is
shown that the thermodynamically most stable chemical ordering in the Pt-Co nanoparticles includes a
first shell fully occupied by Pt atoms, whereas the subsurface layers are Co-rich.
Adsorption, Reaction and Growth Behavior of Carboxylic Acids on Wellordered Oxide Films
T. Xu, M. Schwarz, S. Mohr, M. Amende, M. Laurin, T. Döpper, A. Görling, J. Libuda;
Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany;
Thin layers of functional organic molecules on oxide surfaces hold great potential in applications such as
solar cells and molecular electronics. In spite of the importance of these systems, from a surface science
point of view, little is known about the molecule-oxide bond formation processes at the atomic scale. We
follow a surface science approach to investigate the adsorption of relatively small molecules with
functional groups, such as -COOH, on well-defined oxide surfaces such as MgO(100). The primary
experimental technique is infrared reflection absorption spectroscopy (IRAS), providing information on
bonding geometry and adsorption sites [1].
We have monitored the adsorption of benzoic acid (BA) and phthalic acid (PA) on MgO(100) at 100, 200
and 300 K by time-resolved IRAS. The temperature-dependent changes in the film were monitored by
temperature programmed IRAS. Density functional calculations of the vibrational properties of molecules
in the gas phase were performed. We show that both molecules bind to MgO(100) through carboxyl
group in a tilted bidentate configuration. For BA adsorbed at 100 K, crystallization takes place at 190 K
and multilayer desorption starts at 245 K. For PA, we observe a small fraction of phthalic anhydride
(PAA) which might be formed in the gas phase.
We have also studied the adsorption of BA and PA on rock salt type CoO(111) and spinel type Co3O4(111)
surface. On both surfaces, both acids tend to bind through the carboxyl group. For PA at 100 K, the
molecule tends to form a bis-bidentate carboxylate on Co3O4(111). On CoO(111), however, PA binds
with only one carboxyl group while the other one remains free. At 300 K, only one monolayer of PA
could stabilized on both surfaces which bind in a bis-bidentate fashion. TP-IRAS indicate on both
substrates PA monolayer is stable at least up to 500 K. For BA at 300K, only a monolayer was found on
both surfaces which has similar binding geometry to that of MgO(100). BA monolayer is stable up to 420
K.
[1] S. Schernich, D. Kostyshyn, V. Wagner, N. Taccardi, M. Laurin, P. Wasserscheid, J. Libuda, Journal
of Physical Chemistry C 118, 3188 (2014)
Adsorption, Reaction and Growth Behavior of Carboxylic Acid Anhydrides on
Well-Ordered Oxide Films
S. Mohr1, K. Werner1, T. Xu1, T. Döpper2, Q. Tariq1, O. Lytken1, A. Görling2, M. Laurin1, J.
Libuda1
1
2
Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen,
Theoretische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
Thin layers of functional organic molecules, such as porphyrins, on oxide surfaces offer potential
applications in solar cells or molecular electronics. While the growth and structure of such organic films are
subject to many studies, little is known about the processes of molecule-oxide bond formation at the atomic
scale. To obtain a deeper understanding of the chemical bonding of various anchor groups on oxides we
apply infrared reflection absorption spectroscopy (IRAS) under UHV conditions. Here, IRAS provides
both, information on the molecular orientation and on the molecular interactions of surface-bound
species[1]. As a model oxide surface, we employ an ordered MgO(100) film grown on a Ag(100) single
crystal. Thin films of up to 10 monolayers of MgO were prepared by evaporation of Mg on an Ag(100)
single crystal in O2 atmosphere using well-established preparation procedures.
We have explored the surface interactions of phthalic anhydride at 100 K and 300 K by vaporisation in
vacuo onto the clean MgO/Ag(100). At 300 K the adsorption behaviour of the anhydride was investigated
on a defect MgO/Ag(100) substrate as well as on a hydroxylated MgO/Ag(100) surface. All growth
processes were monitored in-situ by time-resolved IRAS. By comparison to calculated spectra (DFT), we
are able to extract the molecular orientation and identify specific surface interactions. We show that at 100
K phthalic anhydride adsorbs molecularly. The most intense band at 727 cm-1 can be attributed to a
out-of-
-H bending mode. Its high intensity indicates that the molecule is predominantly lying flat
on the surface, before the formation of multilayer occurs. Similar adsorption behaviour of phthalic
anhydride was previously observed on other single crystal surfaces. At 300 K the anhydride ring is broken
up and the molecule binds as a dicarboxylate to the oxide. Adsorption stops after completion of the
monolayer. The dominant modes at 1427 and 1594 cm-1
-1
respectively. Additional small bands at 1776 cm
aC=O)
s
-1
and 1856 cm
sC=O)
aOCO
indicate co-adsorption
of intact anhydride molecules in form of a mixed carboxylate-anhydride structure. Both on a defect
MgO/Ag(100) structure and on the hydroxylated MgO/Ag(100) enhanced formation of surface
dicarboxylate is observed at room temperature.
[1] S. Schernich et al.; Langmuir 30, 6836 (2014)
IR spectroelectrochemistry on thin film and model catalysts prepared under
UHV conditions
Firas Faisal, Olaf Brummel, Matthias Schwarz, Jörg Libuda;
Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
Pt-doped CeO2 has been identified as a potential anode electrocatalyst in proton exchange membrane fuel
cells (PEMFC). Providing very high noble metal efficiency, the material may help to decrease the demand
for Pt, while simultaneously increasing the tolerance against CO poisoning.[1]
To investigate complex model catalysts’ surfaces on single crystals under ultraclean conditions the latter
must be prepared in the ultrahigh vacuum (UHV). To this end we present a UHV system that allows
preparation and characterization of model electrocatalysts and subsequent transfer to an electrochemical
cell without contact to ambient atmosphere. The system is equipped with all standard preparations tools,
electron beam evaporators, thermal evaporator cells and a quartz microbalance. Structural and chemical
analysis is possible by low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and
temperature programmed desorption (TPD). The sample single crystal is transferred through a
differentially pumped stage into the electrolyte without breaking the UHV in the preparation system.
Contamination-free transfer of the prepared single crystal samples are characterized by cyclic
voltammetry (CV).
To explore the chemical state of the Pt species in the ceria matrix under reaction conditions we apply insitu electrochemical IR spectroscopy. Towards this aim we have set up a new IR spectroelectrochemistry
system that includes a state-of-the-art vacuum FTIR spectrometer and an optimized external reflection
cell. We demonstrate that the system is functional and provides an excellent signal/noise ratio.
[1] A. Bruix et al., Angew. Chem. Int. Ed. (2014), 10.1002/anie.201406634.
Operando DRIFTS and mass spectrometry of CO Oxidation on Pt- and RhCeO2 Catalysts
F. Kollhoff, M. Laurin, J. Libuda,
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany,
T-S. Nguyen, F. Morfin, L. Piccolo,
IRCELyon, Lyon, France
Catalytic removal of CO is a challenge for both industry and research that has been gaining attention,
especially because of its importance for fuel cell applications. H2 gas from large scale production
methods often contains large amounts of CO that have to be removed to avoid poisoning of catalysts
employed in fuel cells. A promising method for this is preferential oxidation (PROX) of CO via
heterogeneous catalysis that avoids the oxidation of H2 to H2O.[1] However, commonly used catalysts
for this reaction such as noble metal enhanced oxides are often difficult or expensive to produce.
A novel method for production of CeO2 based catalysts via a one-pot solution combustion synthesis
(SCS) has been applied. This method offers atomic dispersion of the noble metals on the oxide.[2]
CeO2 has been chosen as the oxidefor this project because of its characteristics as reducible oxide.
As a first step towards PROX we tested the catalytic performance of pure CeO2 powder as well as
Pt/CeO2 and Rh/CeO2 powders produced via SCS for the oxidation of CO to CO2 under reaction
conditions in a fixed-bed reactor. Diffuse Reflectance Infrared Fourier Transform Spectroscopy
(DRIFTS) and Quadrupole Mass Spectrometry (QMS) were employed simultaneously in order to
relate surface species with catalytic behavior. QMS data shows that the catalytic behavior of the
powder depends on the metal employed. Moreover, the oxidation state of the oxide and pretreatment
of the oxide have a major influence on the activity for Pt/CeO2 but not on Rh and pristine CeO2.
Analyzing the DRIFTS data, we found that the oxygen coverage of the metal particles on CeO2 seems
to have a major impact on the activity of Pt/CeO2. A smaller amount of adsorbed oxygen on the noble
metal particles prior to a reaction cycle correlated with a lowered temperature necessary for
conversion of CO to CO2.
[1] F. Mariño et al., App. Catal. B, 2004, 54, 59-66.
[2] T-S. Nguyen et al., J. Mat. Chem A, 2014, 46, 19822-19832.
Interactions between the room-temperature ionic liquid [C2C1Im][OTf] and
Pd nanoparticles studied by in-situ infrared spectroscopy
Sascha Mehl, Tanja Bauer, Arafat Toghan, Jörg Libuda
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 3,
91058 Erlangen, Germany
A new concept that helps to improve the selectivity of hydrogenation catalysts involves the
modification of the catalytic materials by thin films of ionic liquids (so-called Solid Catalyst with
Ionic Liquid Layer, SCILL). In a SCILL catalyst, a thin IL film is deposited onto a conventional
heterogeneous catalyst that usually consists of noble metal particles dispersed on an oxide support. In
this case, the IL can alter the reactivity of the noble metal component by a ligand-like interaction or
modify diffusion processes due to the different solubilities of the reactants or possible intermediates
within the IL film. Only a few studies that have dealt with the underlying principles of SCILL
catalysts on an atomic level. Previously, we have studied the interaction of the ionic liquid (IL) 1ethyl-3-methylimidazolium trifluoromethanesulfonate [C2C1Im][OTf] with Pd(111), a well-ordered
film of Al2O3 grown on a NiAl(110) single crystal, and supported Pd nanoparticles by time-resolved
infrared reflection absorption spectroscopy (TR-IRAS).
Here, we extend this work to Pd nanoparticles that are formed directly in the IL by physical vapor
deposition. The IL and the Pd are codeposited unto Au(111) in the presence of a CO atmosphere. IR
spectroscopy of the CO ligand shell that surrounds the Pd particles provides information on the Pd
particle size and structure and well as on its interaction with the IL. We find that particles of different
size can be synthesized and observed in-situ by varying the relative deposition rates of Pd and IL. On
these particles CO adsorbs in on-top and at higher coordinated sites. Upon annealing CO desorbs from
the on-top position. Thermally induced restructuring of the IL shell gives rise to a pronounced redshift of the remaining CO in higher coordinated sites. The latter resides on the Pd nanoparticles up to
temperatures of around 340 K. At higher temperature CO desorbs completely, the IL film restructures
and finally desorbs at 420 K.
[1]
Schernich, S., Kostyshyn, D., Wagner, V., Taccardi, N., Laurin, M., Wasserscheid, P., Libuda,
J., J. Phys. Chem. C 118, 3188 (2014).
In-situ and operando spectroscopy of catalytic materials modified by liquid
films, ionic liquids and molten salts
A. Kaftan, T. Bauer, M. Kusche, V. Hager, P. Wasserscheid, M. Laurin, J. Libuda,
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
A possible solution to improve the performance of supported heterogeneous catalysts is the modification
of the materials by applying an ionic liquid (IL) layer. This modification can enhance the activity and
selectivity of the reaction mainly in two ways: influencing the chemical properties (“cocatalytic effect”)
or provide different solubilities for the reactants (“physical solvent effect”). In this work, we investigate
Pt/Al2O3 catalysts for the water-gas shift (WGS) and methanol steam reforming (MSR) reaction. These
catalysts show remarkably high activity and selectivity after applying a coating of alkali salts.[1,2]
Another investigated system for the purification of a technical feedstock, Pd/Al2O3 coated with the IL
[EMIM][EtSO4], demonstrates the effectiveness of this concept.
The catalytic performance has been tested in a continuous gas-phase fixed-bed reactor and the product
gases were be analyzed online by gas chromatography (GC) or quadrupole mass spectrometry (QMS).
The characterization of the catalyst was performed using diffuse reflectance infrared Fourier transform
spectroscopy (DRIFTS).
Different alkali salt coatings have been investigated for the Pt/Al 2O3 catalyst while it was found that
potassium has the largest influence on the electronic properties of the Pt nanoparticles.[3] Additionally,
potassium salt modified catalysts show a change of the reaction mechanism for WGS and MSR reactions
from formate on uncoated Pt/Al2O3 to carbonate intermediates on coated catalysts.
The IL-coated Pd/Al2O3 catalyst showed in a high-pressure (10 bar) hydrogenation experiment (50 h)
improved selectivity and long-term (50 h) stability although characteristic shifts of vibrational bands
indicate the alkylation of the cation of the IL. This reaction is probably mediated by Pd via an oxidative
addition and subsequent reductive elimination mechanism.
[1]
M. Kusche et al., ChemSusChem 2014, 7, 2516–2526.
[2]
M. Kusche et al., ChemCatChem 2015, 7, 766–775.
[3]
M. Kusche et al., Angew. Chem. Int. Ed. 2013, 52, 5028–5032.
Thin film catalyst for on-chip PEM fuel cells
Tomas.Fej
L.E.T. optomechanika Praha s.r.o
Hostivařská 139/62, 102 00, Praha 15 - Hostivař
Email: [email protected]
We built a new coating instrument, which allows the use of 3 magnetrons with targets up to 4" in
diameter. Thus, 3 different materials can be deposited simultaneously, or sequentially as multilayer
coatings on proton exchange membrane or other substrates.
Presently, the coating instrument is equipped with two magnetrons, one 2" and the other 4" in
diameter. The combinations of materials in coatings made so far were pure Pt, CeO2+Pt (mixed and
multilayer), Ti+Pt, and Ti+Au.
We started the research of fuel cells on chip with a planar fuel cell (FC). This planar FC consists of
two parallel channels approximately 10 mm long covered with proton exchange membrane, coated
with a catalyst on the under-side. An experiment on this elementary planar fuel cell confirmed the
expected functionality. After that we started work on another planar FC, which works with the
effective area of 1 cm^2.
Ab-initio thermodynamics of M-CeO2 solid solutions (M=Pt, Pd, Au) exposing flat
and stepped surfaces
Tran Nguyen Dung, Luigi Bagolini, Matteo Farnesi Camellone and Stefano Fabris
CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, National Research Council & SISSA, Trieste, Italy
Email: [email protected]
The development of highly active catalysts that allow for a more efficient and cleaner use of energy supplies
represents important scientific and technological challenges. A relevant class of heterogeneous catalysts in this
field is constituted by noble metals dispersed on reducible oxide supports like ceria (CeO2). Recently the
stabilization of precious metals either as small clusters or as ionic moieties on high-surface area ceria particles has
been shown to improve several reactions such as low temperature water gas shift, CO oxidation, or methane
combustion.
We have employed density functional theory to investigate the surface structure and stability of different metals
such as Au, Pt, and Pd supported on flat and stepped (111) and (110) ceria surfaces under varying oxygen
pressure and temperature conditions.
Photo-catalytic conversion of CO2 in methanol to methyl formate
over TiO2 catalyst
Pierre-Marie Deleuzea, Alberto Navajasb, Sylvie Bourgeoisa, Bruno Domenichinia
a
Laboratoire Interdisciplinaire Carnot de Bourgogne, ICB, UMR 6303 CNRS, Univ.
Bourgogne Franche-Comté, BP 47870, 21078 Dijon Cedex, France
b
Departamento de Química Aplicada, Edificio de Los Acebos, Universidad Pública de
Navarra, Campus de Arrosadía s/n, E-31006 Pamplona, Spain
Email : [email protected]
Photo-catalytic reactions over solid semiconductors in the form of thin film or suspended
nanoparticles (e.g. titanium dioxide), has been proposed as an environmental friendly process to
remove CO2 product from fossil combustion decreasing CO2 level in the atmosphere [1].
Basically, the reaction involves the conversion of CO2 by a reduction agent (water or methanol)
using UV light and a semiconductor to obtain some hydrocarbons. When a photon interacts with
a photo-catalyst, electron-hole (e--h+) pairs are created. If the photon energy is higher than the
band gap of the semiconductor, the electron will migrate to the conduction band while the hole
stays at the valence band. In order to get high negative and positive redox potentials in the
conduction and valence bands, and by this way to favor oxidation and reduction reactions,
semiconductors with a wide band gap are necessary. Also, these catalysts should be stable
against corrosion, not toxic, not expensive and reusable. TiO2 meets most of these requirements
and several studies tried to increase its photo-catalytic potential by adding Pt, Rh, Au, ..
nanoparticles [2]. This avoids electron-hole (e--h+) recombination and decreases the energetic
barrier for the CO2 reduction.
In this work, TiO2 powders were tested as photo-catalyst in the reduction of CO2 with UV light
using methanol as reduction agent because the strong reducibility and solubility of CO2 in this
alcohol [3]. UV irradiation leads to methyl formate formation studied with GC-MS. It was
shown that the concentration of formed methyl formate is related to the relative amount of TiO2
powders, to the distance between the UV source and the reaction medium and to the time of
CO2 saturation of MeOH. Studies are also in progress on the same kind of reactions performed
on TiO2 thin films modified by Pt and Au.
[1] Cybula A., Flein M., Zaleska A. Appl. Catal. B: Environ. 164 (2015) 433-442.
[2] W. Hou, W.H. Hung, P. Pavaskar, A. Goeppert, M. Aykol, S.B. Cronin, ACS Catalysis. 1 (2011) 929-936.
[3] S. Qin, F. Xin, Y. Liu, X. Yin, W. Ma, J. Coll. Inter. Sci. 356 (2011) 257-261.
Contribution of transmission electron microscopy to the study of catalytic
ceria thin layers
Pardis Simon, Valérie Potin, Céline Dupont, Rémi Chassagnon
Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB) - UMR 6303 CNRS-Univ. Bourgogne
Franche-Comté - 9 av. Alain Savary - 21078 Dijon Cedex- France
E mail: [email protected]
Chemical Vapor Deposition : principles
Nicolas Zanfoni
Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB) - UMR 6303 CNRS-Univ. Bourgogne
Franche-Comté - 9 av. Alain Savary - 21078 Dijon Cedex- France
E mail: [email protected]
Thickness-controlled elaboration of titanium dioxide thin-films on gold
substrates by atomic layer deposition
Maxence Giraudet
Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB) - UMR 6303 CNRS-Univ. Bourgogne
Franche-Comté - 9 av. Alain Savary - 21078 Dijon Cedex- France
E mail: [email protected]
Gold layers elaborated by Physical Vapor Deposition (PVD) processes were used as substrates for the
deposition of thin titanium dioxide films with a varying amount of Atomic Layer Deposition (ALD)
cycles at 280°C. The goal was to obtain compact films, perfectly covering the substrates, with a
controlled thickness varying in the 5-15 nm range. The composition, structure and morphology of
these thin films have been studied by X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy,
Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).
The grown films are composed of stoichiometric TiO2 crystallized in the anatase phase containing a
very small (in 1% range) carbon contamination and having a thickness ranging between 8 and 12 nm
as a function of cycle number and a roughness lower than 2 nm. Films cover the gold film substrates
better than 99.5%. Due to the self-limiting growth mechanism of ALD, the elaborated films have a
precise cycle-controlled thickness and exhibit a compact structure.
Preliminary electrical tests have been carried out on the samples showing that I-V curves exhibit the
characteristics of a tunnel junction diode, meaning the properties of the elaborated titanium dioxide
films are, for instance, satisfying enough to observe quantum tunneling for microelectronic
applications.
Provided that the film thickness is controlled by a proper adjustment of experimental conditions, this
study demonstrates the possibility of obtaining titanium dioxide very thin-films on gold substrate at
quite low temperature using ALD processes.