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3rd International Workshop on Degradation Issues of Fuel Cells and Electrolyzers

The 3rd International Workshop on Degradation Issues of Fuel Cells and Electrolyzers will take place in Santorini, Greece, between Sep. 29 and Oct. 1 2015.
The workshop is co-organized by the CathCat project partners FORTH  and JRC. Several FCH JU projects will participate. CathCat will have a dissemination session there. Further details are available at the website of the workshop.

 

Poster Award at ECS Meeting

During the ECS conference on Electrochemical Energy Conversion and Storage, student poster awards were presented within the Low Temperature Fuel Cells symposium, sponsored by Ion Power. One of the third prizes was awarded to the poster "Electrodeposition of novel catalyst materials for the oxygen reduction reaction" presented by the Ph.D. student Ludwig Asen from TUM in which results from the CathCat project were discusssed.

Project Context and Main Objectives

The electrochemical oxidation of reactants in fuel cells represents, from a thermodynamic point of view, a very efficient way to convert chemical energy into electrical energy. When using hydrogen as fuel, fuel cells represent a very attractive choice as power supply for electric vehicles, with zero local emissions and driving ranges around 500 km. However, the true efficiency is much lower than the thermodynamically possible one. In low temperature proton exchange membrane fuel cells (PEM FCs) this is mainly due to the electrode reactions and especially to the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode. At present, there is demand for a significant increase in electrical efficiency and higher volumetric and gravimetric power densities of fuel cells. State-of-the-art catalysts for both anode- and cathode-side are based on noble metals, mainly Platinum. Especially in mass production, the platinum would significantly add to the total system cost. Also, the production of Pt is not sufficient for widespread implementation of the technology at current loadings. Finally, the lifetime of the fuel cells needs to be improved. The FCH JU has set the following technical targets in the 2011 call regarding performance and durability of PEM fuel cells: Pt loading below 0.15 g/kW, preferentially below 0.1 g/kW, at a BOL efficiency above 55%, BOL powers > 1 W cm-2 @ 1.5 A cm-2, and a lifetime above 5000 h. The aim of the CathCat project is to improve the performance and reduce the cost of PEM cathodes by development of new alloy catalysts based on Pt or Pd as one constituent and Rare Earth Elements as the second constituent. These alloys are known to form thick compressed Pt (or – possibly – Pd) overlayers during initial de-alloying, leading to a significant enhancement of the catalytic activity. Within the project, the possible materials are screened by DFT methods for stability and activity as well as by studies on model alloys based on polycrystalline bulk alloys, single crystalline surface alloys and on thin films. Methods for the preparation of nanoparticles of those materials are developed and up-scaled for MEA production. In parallel, new support materials are explored based on functionalized carbons, carbon nanotubes and oxides. The new support/catalyst combinations are transferred to the cathode side of MEAs that are tested for performance and durability. Benchmarking is done with respect to state of the art catalyst. Aside from low temperature PEMs, the materials are also tested for application in high temperature PEMs, using membranes from Advent technologies. The starting point of the research were significant advances in the theoretical understanding of the deciding factors determining the rate of the ORR at different pure metal and later also alloy surfaces. A number of Pt based alloys form after initial de-alloying Pt skin structures with an outer layer of Pt showing a different lattice constant compared to bulk Pt. This shifts the Pt d-band center and alters the binding energy of ORR intermediates (strain effect). If the skin layer is only one monolayer thick and the underlying layers have a different composition, then the electronic interaction between other elements and the Pt skin also can change this binding energy (ligand effect). While the focus of attention in literature was originally on alloys like Pt3Ni or Pt3Co, that show improved catalytic activity, but low stability and a strong tendency to dealloying, in later work some Pt rare earth alloys were shown to combine increased catalytic activity with enhanced stability, starting with Pt3Y and Pt3Sc, later also including Pt5Gd. These studies are expanded within CathCat, complemented by research on active support materials, ultimately aiming at improved MEAs made from these materials and innovative support materials that meet the targets above.

Description of the work performed and main results so far

At Danmarks Tekniske Universitet (DTU)-CAMD DFT calculations were carried out to predict activity and stability of highly active catalysts. The range of compositions of suitable Pt(Pd)-rare earth (RE) element alloys to be studied was selected. The focus was on catalysts with Pt:RE ratios of 3:1 and higher to prevent leaching out. Since a several layers thick Pt skin forms on Pt-RE alloys, ligand effect and f electrons had not to be considered. Experimental lattice parameters for the Pt alloys were taken to determine the strain, and the OH binding energy was modelled. The influence of surface reconstruction was discussed, and comparison to experimental activities made. All Pt-RE alloys exhibit activities higher than that of Pt. For studies on Pd, the scaling relations between the binding strength of different intermediates were reinvestigated specifically for strained Pd. This allows to predict the activity changes of Pd by alloying. The theoretical findings were confirmed at UniPd by experimental studies on a Pd model alloy. At DTU-CINF, studies on polycrystalline Pt-RE alloys were carried out. ORR RDE measurements of sputter-cleaned Pt5Gd showed a 5-fold increase in activity relative to Pt at 0.9 V in 0.1 M HClO4, and Pt5La and Pt5Ce more than a 3-fold enhancement. Angle resolved XPS (AR-XPS) was performed before and after testing for reconstructing the surface structure. Depth profiles of Pt5La and Pt5Ce after electrochemistry exhibited the formation of a thick Pt overlayer, as previously observed for Pt5Gd. The catalysts were very stable, losing less than 15% of their initial activity after 10 000 cycles between 0.6 V and 1.0 V. Further studies concerned UHV prepared Pt(111)-Y surface alloys, and mass-selected PtxY nanoparticles. The latter also demonstrated exceptional catalytic activity. These findings confirmed theoretical predictions. At Chalmers, substrates for investigating catalyst nanoparticles via indirect nanoplasmonic sensing were prepared and tested with Pt nanoparticles. A major challenge is the large scale synthesis of these alloys as nanoparticles for MEA fabrication. Efforts regarding the synthesis of Pt-rare earth alloys included solution-based methods, namely the carbonyl method and the water-in-oil route applied at Université de Poitiers (UP), electrochemical methods at TUM and gas phase reduction of precursors at elevated temperatures at University of Padova (UniPd). None of these routes has been fully successful yet, but interesting results and materials have been obtained. The water-in-oil route led to Y-/Gd-oxide modified Pt nanoparticles that showed an increased catalytic activity at 0.9 V. The Y-based catalyst was prepared in an amount sufficient for MEA preparation at Ion Power. In collaboration with FORTH, the catalyst was also studied on modified carbon nanotubes. The gas phase reduction at UniPd led to a catalyst outperforming pure Pt. At FORTH, a modified polyol process was applied for the preparation of Pt-Co catalyst. Depending on the exact nature of the carbon nanotube supports used, formation of a Pt3Co alloy was observed or not. Further work focused on advanced support materials: N-Ion implantation in HOPG did not improve the catalytic activity of Pd nanoparticles, as shown by UniPd and TUM. Therefore UniPd focussed on the development of functionalized mesoporous carbons as advanced support materials, and found improved catalytic activities for both Pd and Pt. They also explore graphene oxide based materials. At UP, TiO2 composites and mixed Ti-metal oxides (e.g. Ti-W-oxides) were studied. One of the latter oxides showed a significantly enhanced catalytic activity of supported metal nanoparticles. All the materials prepared were characterized with respect to ORR, composition and structure. Changes during electrochemical reactions were monitored. Benchmark measurements were carried out in half cell configuration and in low (Ion Power, Toyota, JRC) and high temperature (FORTH) MEAs.

Description of the expected final results and their potential impact and use

This project will exceed the state of the art both from a fundamental point of view as well as from the application point of view. New improved catalysts with increased activity and decreased Pt content will be developed, studied, made into NPs, supported onto advanced supports and manufactured into advanced MEAs. Both the catalysts and the MEAs will be tested with respect to performance and durability. Different strategies have in the meantime be devised to solve the problems with the large scale nanoparticle preparation from Pt-rare earth alloys. Several improved nanoparticular catalyst systems have already been developed within the project, and studies on new advantageous support materials have resulted in further improvements and new ideas. Together with the anticipated progress in the second half of the project, finally several (planned: 5+) MEAs with new cathode catalysts and advanced support materials types will have been developed, that outperform the benchmark MEAs and fulfil the FCH JU targets. The research in CathCat will allow a significant reduction and/or the replacement of Pt in MEAs and therefore enable a vast improvement in commercial cost of PEMFCs allowing for commercialization and wide range application in automotive industry. In addition the research has led and will further lead to an improved understanding of electrocatalysis and support/catalyst interactions that in turn can be applied to design new, even more powerful materials. Also the activities regarding the synthesis of nanoparticles and advanced support materials improve the portfolio of available techniques that can be applied for materials synthesis even for applications outside catalysis or electrocatalysis. The use of two different types of advanced membrane materials will provide the relevant data for the operation of the improved catalyst layers at a large range of operation temperatures, and warrants the transferability of the technology to new developments in the field of membranes and gas diffusion layers in the next years. It is expected that at the end of the project the technology and the catalyst design for improved MEAs have been developed and are available for stack testing and commercialisation in cooperation between the industrial partners in the consortium. The knowledge gained through CathCat has already resulted in eight publications, and several more will follow within the next months. The results will have economic, social and environmental impact. The development of novel catalyst materials through this project would lead to a reduction in fuel cell production costs, and to an increased lifetime, leading to an increased total cruising range of the fuel cell. This will help to enhance the competitiveness of the European fuel cell industry. Also the new synthesis methods developed in this project can be commercialized. Economic prosperity and quality of life depend crucially on the provision of secure clean energy at competitive prices. Fuel cells running on hydrogen derived from a renewable source could offer significant improvements to local air quality. Electric cars based on fuel cells with long life-span and low cost fuel cells could provide electromobility without the disadvantages of battery driven cars, like limited driving range, high costs and safety issues. CathCat has the prospect to improve the performance and reduce the cost of these emerging technologies, facilitating their market introduction. The fore-seen economic impact will create new options for employment within the industry. A hydrogen-based energy economy, if the hydrogen is produced from a sustainable source, has the potential to significantly reduce greenhouse gas emissions and therefore assist in combating the effects of climate change. The project also contributes to the education of young people in the field of electrocatalysis, electrochemistry and fuel cells, as the experimental work is mainly carried out by young postdocs and Ph.D. students.

Conference Presentations

1. M. Escudero-Escribano, A. Verdaguer-Casadevall, P. Malacrida, U. Grønbjerg, B. P. Knudsen, J. Rossmeisl, I. E. L. Stephens, I. Chorkendoff, Pt5Gd as a highly active and stable catalyst for oxygen electroreduction, 7th International Symposium Hydrogen and Energy, Stoos (Switzerland), January 2013. Oral communication.

2. J. Ma, A. Habrioux, C. Morais, N. Alonso-Vante, Tolerance effect by tuning substrate and catalysts centers entities. 223rd ECS Meeting Toronto, Ontario, Canada, May 12 – 16, 2013.

3. I. Chorkendorff, Electro-catalytic Oxygen Reduction. The SUNCAT Summer Institute, SLAC Stanford University, Menlo Park, CA USA,August 25-30, 2013.

4. I. Chorkendorff, New electro-catalyst alloys for the Oxygen Reduction Reaction (ORR) and Hydrogenperoxide production. Swiss Chemical Society Fall Meeting, Lausanne, September 06, 2013.

5. J. Ma, A. Habrioux, N. Alonso-Vante, Probing the Interaction Between Platinum Nanoparticles and Graphitic Domains of Carbon, 64th Annual Meeting 2013 of the International Society of Electrochemistry, Santiago de Queretaro, Mexiko, 08-13.09.2013.

6. I. Chorkendorff, Rational Design of Oxygen Reduction Reaction and Hydrogen Peroxide Catalysts: From Surface Science to Nanoparticles. 2nd Annual SFB FOXSI Symposium, Conference Center Burg Schlaining, Stadtschlaining, Austria, September 18-20, 2013

7. M. Escudero-Escribano, U. Grønbjerg, P. Malacrida, A. Verdaguer-Casadevall, J. Rossmeisl, J. Schiøtz, I. E. L. Stephens, I. Chorkendoff, “Trends in the activity and stability of Pt-alloy catalysts for the ORR: a focus on novel alloys of Pt and lanthanides”, 64th Annual Meeting 2013 of the International Society of Electrochemistry, Santiago de Queretaro, Mexiko, 08-13.09.2013.

8. Christian Durante, Lorenzo Perini, Marco Favaro, Stefano Agnoli, Gaetano Granozzi and Armando Gennaro, “Electrocatalysis at Pd Nanoparticles: Effect of the Support Nitrogen Doping on the Catalytic Activation of Carbon-Halogen Bond”, 64th Annual Meeting 2013 of the International Society of Electrochemistry, Santiago de Queretaro, Mexiko, 08-13.09.2013.

9. Lorenzo Perini, Christian Durante, Silvia Leonardi, Oliver Schneider, Julia Kunze, Gaetano Granozzi, Armando Gennaro; “Synthesis of Nitrogen Doped Mesoporous Carbon Catalyst Supported with Metal Nanoparticles for the Oxygen Reduction Reaction”, 64th Annual Meeting 2013 of the International Society of Electrochemistry, Santiago de Queretaro, Mexiko, 08-13.09.2013.

10. L. Perini, C. Durante, S. Leonardi, O. Schneider, J. Kunze, M. Favaro, G. Granozzi, A. Gennaro, “Platinum And Palladium Nanoparticle Catalysts Supported On Activated Mesoporous Carbon For The Oxygen Reduction Reaction”, Italian Meeting of Electrochemistry GEI 2013, 22-27 September, Pavia.

11. B. Wickman, J. Hagberg, C. Langhammer, "Combining Electrochemical and In-Situ Optical Detection on Pt and Pd Thin-Films”, Hydrogen and Fuel Cells in the Nordic Countries 2013, Oslo, Norway, October 31 – November 1, 2013.

12. M. Escudero-Escribano, "Enabling low-temperature fuel cells via improved Pt-based cathode catalysts”, European Hydrogen Energy Conference 2014, Sevilla, Spain, March 12 – 14, 2014.

13. I. Chorkendorff, "Mass-selected Nanoparticles for Heterogeneous and Electro-Catalysis”, CSI 2014: Cluster Surface Interaction, Lake Varese, Italy, June 1-4, 2014.

14. J. Ma, A. Habrioux, C. Morais, N. Alonso-Vante,"Methanol-tolerant Cathode Catalysts for DMFC”, CIMTEC 2014, 6th Forum on New Materials, Montecatini Terme, Italy, June 16 – 19, 2014.

15. N. Alonso-Vante, "Advanced Nanomaterials for Oxygen Reduction Process”, 65th Annual ISE Meeting, Lausanne, Switzerland, August 31 - September 05, 2014. 

16. A. Velázquez-Palenzuela, F. Masini, A.F. Pedersen, M. Escudero-Escribano, D. Deiana, P. Malacrida, T.W. Hansen, D. Friebel, A. Nilsson, I.E.L. Stephens, I. Chorkendorff, "Oxygen Reduction on Mass-selected PtxGd Nanoparticles as Model Catalysts for Fuel Cells”, 65th Annual ISE Meeting, Lausanne, Switzerland, August 31 - September 05, 2014 (oral contribution).

17. I.E.L. Stephens, "Combining experiment and theory in the search for new electrocatalysts for oxygen electroreduction to H2O and H2O2”, 65th Annual ISE Meeting, Lausanne, Switzerland, August 31 - September 05, 2014 (Keynote).

18. J. Ma, L. Seidl, W. Ju, E. Mostafa, L. Asen, S. Martens, U. Stimming and O. Schneider, "Applications of Ionic Liquids in Electrochemical Energy Conversion and Storage”, 226th Meeting of the Electrochemical Society, Cancun, Mexiko, October 05-09, 2014.

19. W. Ju, T. Brülle, M. Favaro, S. Agnoli, G. Granozzi, O. Schneider, U. Stimming, "Electrocatalytic Activity and Stability of Supported Palladium Nanoparticles”, 226th Meeting of the Electrochemical Society, Cancun, Mexiko, October 05-09, 2014 (Poster). 

20. Maria Escudero-Escribano, Paolo Malacrida, Ulrik Grønbjerg Vej-Hansen, Vladimir Tripkovic, Jan Rossmeisl, Ifan E.L. Stephens, Ib Chorkendorff; "Engineering the Activity and Stability of Pt-Alloy Cathode Fuel-Cell Electrocatalysts by Tuning the Pt-Pt Distance”, 226th Meeting of the Electrochemical Society, Cancun, Mexiko, October 05-09, 2014 (oral communication).

21. P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, U. Grønbjerg, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff; "Pt-Lanthanide Alloys for Oxygen Reduction: Relating Active Surface Phase and Catalytic Performance”, 226th Meeting of the Electrochemical Society, Cancun, Mexiko, October 05-09, 2014 (oral communication).

22. I.E.L. Stephens; "Tailoring Platinum Group Metals Towards Optimal Activity for Oxygen Electroreduction to H2O and H2O2: From Extended Surfaces to Nanoparticles”, 226th Meeting of the Electrochemical Society, Cancun, Mexiko, October 05-09, 2014 (invited).

Summary of first year results

Objectives

The aim of the CathCat project is to improve the performance and reduce the cost of PEM cathodes by development of new alloy catalysts based on Pt or Pd as one constituent and Rare Earth Elements as the second constituent. These alloys are known to form thick compressed Pt (or – possibly – Pd) overlayers during initial de-alloying, leading to a significant enhancement of the catalytic activity [1-4]. Within the project, the possible combinations are screened by DFT methods for stability and activity as well as by the use of model alloys based on single- and polycrystalline bulk alloys and on thin films. Methods for the preparation of nanoparticles of those materials are developed and up-scaled for MEA production. In parallel, new support materials are explored based on functionalized carbons, carbon nanotubes and oxides. The new support/catalyst combinations are transferred to the cathode side of MEAs that will be tested for performance and durability. Benchmarking will be done with respect to state of the art catalyst.

The starting point of the research within CathCat were significant advances in the theoretical understanding of the deciding factors determining the rate of the oxygen reduction reaction at different pure metal and later also alloy surfaces [5-9]. A number of Pt based alloys form after initial dealloying Pt skin structures with an outer layer of Pt showing a different lattice constant compared to bulk Pt [1, 3]. This leads to a shift in the d-band center of the Pt and therefore to a modulation in the binding energy of ORR intermediates [7] (strain effect) [1, 10]. If the skin layer is only one monolayer thick and the underlying layers have a different composition, then the electronic interaction between other elements and the outer Pt skin also can change this binding energy (ligand effect) [1, 10]. While the focus of attention was originally on alloys like Pt3Ni or Pt3Co, that show improved catalytic activity, but low stability and a strong tendency to dealloying [1, 7], in later work some Pt rare earth alloys were shown to combine increased catalytic activity with enhanced stability, starting with Pt3Y and Pt3Sc [5, 11], later also including Pt5Gd [4]. These studies are expanded within CathCat, ultimatively aiming at improved MEAs made from these materials and innovative support materials.

 

The focus of the first year of research was to expand the fundamental theoretical and experimental studies to alloys with different rare earth elements and different conditions, and to work on the preparation of nanoparticles of Pt-Y and Pt-Gd alloys. A number of different approaches like vacuum based techniques for more fundamental studies, chemical and electrochemical techniques were explored, and tests of the ORR activity using conventional tests setups in three electrode configurations and aqueous electrolytes were carried out.

 

Fundamental Work

The theoretical work in the first year focused on the selection of the most promising alloy compositions and the calculation of activity, stability, and structural properties. The OH-binding energies for Pt alloys Pd alloys with a number of rare earth elements were calculated. As these alloys – at least for the Pt alloys – form a several layers thick overlayer of pure Pt, only the strain effect influences the results. For some alloys, an ORR activity much larger than for Pt is expected from the calculations.

 

At DTU, studies on polycrystalline Pt-rare earth alloys were carried out. Alloys of Pt with early transition metals or lanthanides, such as Pt3Y, Pt5Gd, Pt5La, Pt5Sm, Pt5Tm and Pt5Ce, present exceptionally negative alloying energy [2, 12]. Motivated by this, Malacrida and co-authors have studied Pt5La, Pt5Ce, and Pt5Gd polycrystalline samples as cathode electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Rotating disk measurements show that sputter-cleaned, polycrystalline Pt5Gd shows a 5-fold increase in ORR [4], and all the previously mentioned alloys exhibit more than a 3-fold activity enhancement [2], relative to Pt at 0.9 V in 0.1 M HClO4.

In order to follow the chemical state of the catalytic surfaces, angle resolved XPS (AR-XPS) was performed before and after all the preparation and testing steps. By discerning the XPS spectra at different emission angles, AR-XPS is a powerful technique for reconstructing the surface structure of these catalysts. The presence of a Pt overlayer explains the increase in the Pt to La and Pt to Ce ratios, from the initial values measured during sputtering. This is particularly evident for higher angles due to the higher surface sensitivity. Depth profiles of Pt5La and Pt5Ce after electrochemistry were calculated from the data. Both catalysts exhibit the formation of a thick Pt overlayer, as had been previously observed for Pt5Gd [4]. The stability of the alloys under ORR conditions was tested by applying consecutive cycles from 0.6 to 1.0 V vs. RHE in an O2-saturated 0.1 M HClO4 electrolyte at 100 mV s−1 and 23 °C. Not only are the catalysts highly active, they are also very stable, losing less than 15% of their initial activity after 10 000 cycles between 0.6 V and 1.0 V.After 10 000 potential cycles in the above described conditions, the final specific activity of Pt5La, Pt5Ce and Pt5Gd is still more than 3 times higher than for pure Pt.

 

At Chalmers, Hole-Mask Colloidal Lithography (HCL) has been the work-horse for nanofabrication since 2007 [13]. It is based on electrostatic self-assembly when forming the mask and allows for efficient fabrication of quasi-random arrays of nanoparticles such as disks, ellipses or pairs on a support material of choice and covering large areas (cm2) homogeneously, if required. Typically, particle sizes between 20 nm and up to several 100 nm can easily be achieved and controlled, and any metal that either can be deposited by thermal evaporation or by sputtering can be used. Figure 1 shows arrays of 120 nm (left) or 50 nm (right) Pt nanodisk arrays fabricated by HCL.

 

     

 

Figure 1. SEM images of arrays of Pt catalyst nanodisks with 120 nm (left) and 50 nm (right) diameter.

 

Plasmonic nanoantennas create locally strongly enhanced electric fields in so-called hot spots. To place a relevant nano-object with high accuracy in such a hot spot it is crucial to fully capitalize on the potential of nanoantennas to probe and enhance processes at the nanoscale on an adjacent, e.g., catalyst nanoparticle. For this purpose at Chalmers the bottom-up and self-assembly-based Shrinking-Hole Colloidal Lithography (SHCL) [14, 15] nanofabrication method was developed, which provides (i) unique control of the size and position of subsequently deposited particles forming the nanoantenna itself, and (ii) allows delivery of catalytic nanoobjects consisting of a material of choice to the antenna hot spot – all in a single lithography step and, if desired, uniformly covering several cm2 of surface. The SHCL technique is characterized by high flexibility in terms of exploited materials, absence of contamination of the grown structures after fabrication or alteration of deposited material properties. This opens unique possibilities for the fabrication of model catalysts where one can probe oxidation/reduction processes, corrosion processes or the role of position and interplay of the noble metal catalyst and (oxidic or conducting, e.g. carbon) support via spill-over. If implemented on a conducting support like carbon or a transparent conducting oxide, this approach should be perfectly compatible with electrochemistry.

 

In order to simultaneously measure nanoplasmonic signal and electrochemistry on the model catalysts, an electrochemical window cell has been designed and manufactured. The cell is a flow cell where electrolyte is supplied from a gas bubbled reservoir. Optical measurements can be conducted in either transmission mode (i.e. collecting the light that passes through the sample) or reflection mode. To validate the setup, thin films of Pt and Pd have been measured with in-situ optical characterization. The technique will be developed further, e.g. to also analyze nanoplasmonic signals. Preliminary measurements on stability (not shown) indicate that this optical technique can offer valuable insight also into corrosion of fuel cell catalysts.

 

At University of Padova, a transfer system for the transfer between an electrochemical cell and UHV equipment for surface analysis and sample preparation was constructed. In addition electrochemical studies of Pt and Pd on undoped and doped carbon materials were carried out, including experiments on carbon model substrates. Nitrogen doping of HOPG was studied at two different implantation energies, followed by XPS analysis, and pure Pd nanoparticles were deposited on the samples both by vacuum deposition and electrochemical techniques. The stability of the particles and the electrocatalytic activity with respect to ORR were studied. No significant improvement of the electrocatalytic activity of these samples by nitrogen functionalization was found. Pd NPs were also deposited; following an electrochemical approach, on a nitrogen doped glassy carbon (N-GC) [16]. The N-GC samples were prepared by using both ion implantation and by electrochemical oxidation in a phosphate buffer containing 0.1 M carbamic acid. In the former case a nitrogen content of 15% was obtained whereas in the latter case only 5.7 % was observed. The deposition of Pd NPs on N-GC (Pd@N-GC) has been carried out by double step potential electrodeposition from a 1M HClO4 solution with 1 mM PdSO4. In the case of N-GC prepared via the two different approaches, the NPs are spherical in shape with average dimension of 20 nm and are uniformly distributed over the N-GC surface. On the opposite, the deposition of Pd on pure GC results in the formation of NPs of average dimension of 40 nm but also in the presence of NP clusters of 100-300 nm. It is clear that the electrodeposition of Pd on N-doped GC results in a better nucleation than on GC and this is probably the result of a much stronger interaction between defect sites of GC and Pd. The two differently doped GC surface and pristine GC loaded with Pd NPs were characterized by means of XPS. The surveys for all three samples clearly show similar features that account for the presence of Pd, carbon and oxygen, while nitrogen is present only in the case of Pd@N-GC. In Pd@N-GC, one can distinguish between different chemical defects; by deconvoluting the N 1s XPS peak, one can single out the presence of pyridinic (398.0 eV), –CºN terminal groups, pyrrolic, N graphitic defects and N+ ions trapped into carbon vacancies. A further component present at high binding energy can be assigned to the interaction between nitrogen and oxygen with the formation of NOx groups, though in a very limited amount. In the case of Pd@N-GC prepared via electrochemical doping aminic and pyrrolic groups are predominant with respect to other chemical defects such as pyridinic or graphitic nitrogen, that are however consistently present. In order to transfer the N-functionalization to materials suitable for fuel cells, mesoporous carbon materials were studied as well. At TU München, research on electrochemical Pd deposition on different carbon substrates was carried out, in part in collaboration with Padova [17, 18].

 

Nanoparticle Synthesis and Characterization

At DTU, research on size selected nanoclusters of alloy nanoparticles was carried out [19]. The synthesis of such nanoparticles was also carried out with chemical methods at University of Poitiers, and first results indicate a significant improvement of catalytic activity and good stability of some of these catalysts. At FORTH Institute, Pt-Co nanoparticles were made and supported on carbon nanotubes.

 

MEA Testing

MEAs for low temperature fuel cells are manufactured by Ion Power, while those for HT fuel cells are made by FORTH Institute. HT PEMFCs having certain advantages over the state-of-the-art low temperature fuel cells constitute a key research issue aiming at higher efficiencies, cost reduction and compactness. The state-of-the-art HT technology is based on phosphoric acid doped polymer membranes as the electrolyte. As such, FORTH Institute chose to work with Advent Technologies high temperature polymer electrolyte. For this type of cells, within the framework of previous FCH JU projects, a Pt based electrocatalyst with improved features was developed [20]. CNTs were used as the catalyst support due to their high specific surface area, unique electrical, mechanical and thermal properties, as well as the fact that CNTs have been reported to be more corrosion resistant than carbon black. Towards the development of an optimized electrocatalytic system, there are two important considerations; the deposition of fine Pt particles on the carbon support and the construction of an electrocatalytic layer where they can thoroughly participate in the electrocatalytic active network of a 3D structured electrochemical interface, thus aiming at the total utilization of Pt particles’ specific surface area. In this respect, the idea was to transfer the concept of the electrolyte into the catalytic layer (CL). This was accomplished by the covalent attachment and uniform distribution of polar pyridine moieties throughout the CL, which are expected to interact with phosphoric acid originating either by doping the electrode or from the electrolyte. Thus the acid–base interaction of the H3PO4 with the pyridines will ensure the uniform distribution of the acid so that a 3D proton ionic link will provide an active electrochemical interface with all deposited Pt particles. Only particles, which are connected to both electrolyte (PA) and current collector (CNTs) can contribute to the real surface area. The catalysts have been thoroughly characterized by relevant techniques. MEAs were homemade using these catalysts and new ones, and characterized for electrochemical active surface area and other properties. Finally fuel cell tests at 180°C were carried out, showing good performance.

 

 

References

[1] I.E.L. Stephens, A.S. Bondarenko, U. Gronbjerg, J. Rossmeisl, I. Chorkendorff, Understanding the electrocatalysis of oxygen reduction on platinum and its alloys, Energy & Environmental Science, 5 (2012) 6744-6762.

[2] P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, I.E.L. Stephens, I. Chorkendorff, Enhanced activity and stability of Pt-La and Pt-Ce alloys for oxygen electroreduction: the elucidation of the active surface phase, Journal of Materials Chemistry A, doi: DOI: 10.1039/C3TA14574C (2014).

[3] I.E.L. Stephens, A.S. Bondarenko, L. Bech, I. Chorkendorff, Oxygen Electroreduction Activity and X-Ray Photoelectron Spectroscopy of Platinum and Early Transition Metal Alloys, ChemCatChem, 4 (2012) 341-349.

[4] M. Escudero-Escribano, A. Verdaguer-Casadevall, P. Malacrida, U. Grønbjerg, B.P. Knudsen, A.K. Jepsen, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, Pt5Gd as a Highly Active and Stable Catalyst for Oxygen Electroreduction, Journal of the American Chemical Society, 134 (2012) 16476-16479.

[5] J. Greeley, I.E.L. Stephens, A.S. Bondarenko, T.P. Johansson, H.A. Hansen, T.F. Jaramillo, J. Rossmeisl, I. Chorkendorff, J.K. Nørskov, Alloys of platinum and early transition metals as oxygen reduction electrocatalysts, Nature Chemistry, 1 (2009) 552-556.

[6] J.K. Norskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J.R. Kitchin, T. Bligaard, H. Jonsson, Origin of the overpotential for oxygen reduction at a fuel-cell cathode, Journal of Physical Chemistry B, 108 (2004) 17886-17892.

[7] V. Stamenkovic, B.S. Mun, K.J.J. Mayrhofer, P.N. Ross, N.M. Markovic, J. Rossmeisl, J. Greeley, J.K. Nørskov, Changing the Activity of Electrocatalysts for Oxygen Reduction by Tuning the Surface Electronic Structure, Angewandte Chemie-International Edition, 45 (2006) 2897 –2901.

[8] J. Rossmeisl, J.K. Nørskov, Electrochemistry on the computer: Understanding how to tailor the metal overlayers for the oxygen reduction reaction (A perspective on the article, ‘‘Improved oxygen reduction reactivity of platinum monolayers on transition metal surfaces”, by A.U. Nilekar and M. Mavrikakis), Surface Science, 602 (2008) 2337–2338.

[9] V. Tripković, E. Skúlason, S. Siahrostami, J.K. Nørskov, J. Rossmeisl, The oxygen reduction reaction mechanism on Pt(111) from density functional theory calculations, Electrochimica Acta, 55 (2010) 7975-7981.

[10] T. Bligaard, J.K. Nørskov, Ligand effects in heterogeneous catalysis and electrochemistry, Electrochimica Acta, 52 (2007) 5512-5516.

[11] S.J. Yoo, K.-S. Lee, S.J. Hwang, Y.-H. Cho, S.-K. Kim, J.W. Yun, Y.-E. Sung, T.-H. Lim, Pt3Y electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells, International Journal of Hydrogen Energy, 37 (2012) 9758-9765.

[12] I.E.L. Stephens, J. Rossmeisl, M.E. Escribano, A. Verdaguer-Casadevall, P. Malacrida, U.G. Vej-Hansen, B.P. Knudsen, A.K. Jepsen, I. Chorkendorff, Platinum and palladium alloys suitable as fuel cell electrodes, Patent, WO2014005599A1, in, Danmarks Tekniske Universitet, Denmark, 2014, pp. 39pp.

[13] H. Fredriksson, Y. Alaverdyan, A. Dmitriev, C. Langhammer, D.S. Sutherland, M. Zäch, B. Kasemo, Hole–Mask Colloidal Lithography, Advanced Materials, 19 (2007) 4297-4302.

[14] B. Wickman, H. Fredriksson, S. Gustafsson, E. Olsson, B. Kasemo, Fabrication of poly- and single-crystalline platinum nanostructures using hole-mask colloidal lithography, electrodeposition and annealing, Nanotechnology, 22 (2011) 345302.

[15] S. Syrenova, C. Wadell, C. Langhammer, Shrinking-hole colloidal lithography - self-aligned nanofabrication of complex plasmonic nanoantennas, submitted (2014).

[16] L. Perini, C. Durante, M. Favaro, S. Agnoli, G. Granozzi, A. Gennaro, Electrocatalysis at palladium nanoparticles: Effect of the support nitrogen doping on the catalytic activation of carbonhalogen bond, Applied Catalysis B: Environmental, 144 (2014) 300-307.

[17] W. Ju, T. Brülle, M. Favaro, L. Perini, C. Durante, O. Schneider, U. Stimming, Palladium Nanoparticles Supported on HOPG: Preparation, Reactivity and Stability, Electrochim. Acta, in preparation (2014).

[18] W. Ju, M. Favaro, C. Durante, L. Perini, S. Agnoli, O. Schneider, U. Stimming, G. Granozzi, Pd Nanoparticles deposited on nitrogen-doped HOPG: New Insights into the Pd-catalyzed Oxygen Reduction Reaction, Electrochim. Acta, submitted (2014).

[19] P. Hernández-Fernández, I.E.L. Stephens, I. Chorkendorff, Mass-selected nanoalloys as model catalysts: PtxY nanoparticles for oxygen electroreduction, submitted (2014).

[20] A. Orfanidi, M.K. Daletou, S.G. Neophytides, Preparation and characterization of Pt on modified multi-wall carbon nanotubes to be used as electrocatalysts for high temperature fuel cell applications, Appl. Catal. B-Environ., 106 (2011) 379-389.

 

List of Publications

Review Papers

Jiwei Ma, Aurélien Habrioux, and Nicolas Alonso-Vante; The Effect of Substrates at Cathodes in Fuel Cells, ChemElectroChem, 1 (2014) 37-46.

 

Journal Articles

S. Mokrane-Soualah, A.S. Gago, A. Habrioux, N. Alonso-Vante, Mixed-oxide Ti1−xWxO2 as support for (photo)-electrochemical processes, Applied Catalysis B: Environmental, 147 (2014) 756-763.

S. Siahrostami, A. Verdaguer-Casadevall, M. Karamad, D. Deiana, P. Malacrida, B. Wickman, M. Escudero-Escribano, E.A. Paoli, R. Frydendal, T.W. Hansen, I. Chorkendorff, I.E.L. Stephens, J. Rossmeisl, Enabling direct H2O2 production through rational electrocatalyst design, Nature Materials, 12 (2013) 1137-1143.

L. Perini, C. Durante, M. Favaro, S. Agnoli, G. Granozzi, A. Gennaro, Electrocatalysis at palladium nanoparticles: Effect of the support nitrogen doping on the catalytic activation of carbon halogen bond , Applied Catalysis B: Environmental, 144 (2014) 300-307.

P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, I.E.L. Stephens, I. Chorkendorff, Enhanced activity and stability of Pt-La and Pt-Ce alloys for oxygen electroreduction: the elucidation of the active surface phase , Journal of Materials Chemistry A, 2 (2014) 4234-4243.

Y. Luo, A. Habrioux, L. Calvillo, G. Granozzi, N. Alonso-Vante, Yttrium Oxide/Gadolinium Oxide-Modified Platinum Nanoparticles as Cathodes for the Oxygen Reduction Reaction, Chemphyschem, 15 (2014) 2136–2144.

Wenbo Ju, Marco Favaro, Christian Durante, Lorenzo Perini, Stefano Agnoli, Oliver Schneider, Ulrich Stimming and Gaetano Granozzi, Pd Nanoparticles deposited on nitrogen-doped HOPG: New Insights into the Pd-catalyzed Oxygen Reduction Reaction , Electrochimica Acta, 141 (2014) 89-101.

T.P. Johansson, E.T. Ulrikkeholm, P. Hernandez-Fernandez, M. Escudero-Escribano, P. Malacrida, I.E.L. Stephens, I. Chorkendorff, Towards the elucidation of the high oxygen electroreduction activity of PtxY: surface science and electrochemical studies of Y/Pt(111), Physical Chemistry Chemical Physics, 16 (2014) 13718-13725.

Marco Favaro, Lara Ferrighi, Gianluca Fazio, Luciano Colazzo, Cristiana Di Valentin,Christian Durante, Francesco Sedona, Armando Gennaro, Stefano Agnoli, and Gaetano Granozzi, Single and Multiple Doping in Graphene Quantum Dots: Unraveling the Origin of Selectivity in the Oxygen Reduction Reaction, ACS Catalysis, 5 (2015) 129-144.

Wenbo Ju, Tine Brülle, Marco Favaro, Lorenzo Perini, Christian Durante, Oliver Schneider, Ulrich Stimming, Palladium Nanoparticles Supported on HOPG: Preparation, Reactivity and Stability, ChemElectroChem, 2 (2015) 547-558.

Lorenzo Perini, Christian Durante, Marco Favaro, Valentina Perazzolo, Stefano Agnoli, Oliver Schneider, Gaetano Granozzi, and Armando Gennaro, Metal−Support Interaction in Platinum and Palladium Nanoparticles Loaded on Nitrogen-Doped Mesoporous Carbon for Oxygen Reduction Reaction, ACS Appl. Mater. Interfaces, 7 (2015) 1170-1179.

C.M. Pedersen, M. Escudero‐Escribano, A. Velázquez‐Palenzuela, L.H. Christensen, I. Chorkendorff, and I.E.L. Stephens, Benchmarking Pt‐based electrocatalysts for low temperature fuel cell reactions with the rotating disk electrode: oxygen reduction and hydrogen oxidation in the presence of CO, Electrochimica Acta, 179 (2015) 647–657.

J. Ma, A. Habrioux, Y. Luo, G. Ramos Sanchez, L. Calvillo, G. Granozzi, P.B. Balbuena, and N. Alonso-Vante, Electronic Interaction between Platinum Nanoparticles and Nitrogen-doped Reduced Graphene Oxide: Effect on the Oxygen Reduction Reaction, Journal of Materials Chemistry A, 3 (2015) 11891-11904.

Y. Luo, A. Habrioux, L. Calvillo, G. Granozzi, and N. Alonso-Vante, Thermally Induced Strains on the Catalytic Activity and Stability of Pt–M2O3/C (M=Y or Gd) Catalysts towards Oxygen Reduction Reaction, ChemCatChem, 7 (2015) 1573–1582.

Y. Luo and N. Alonso-Vante, The Effect of Support on Advanced Pt-based Cathodes towards the Oxygen Reduction Reaction. State of the Art, Electrochimica Acta, 179 (2015) 647–657.

M. Favaro, F. Carraro, M. Cattelan, L. Colazzo, C. Durante, M. Sambi, A. Gennaro, S. Agnoli, and G. Granozzi, Multiple doping of graphene oxide foams and quantum dots: new switchable systems for oxygen reduction and water remediation, Journal of Materials Chemistry A, 3 (2015) 14334-14347.

Amado Velázquez-Palenzuela, Federico Masini, Anders F. Pedersen, María Escudero-Escribano, Davide Deiana, Paolo Malacrida, Thomas W. Hansen, Daniel Friebel, Anders Nilsson, Ifan E.L. Stephens, Ib Chorkendorff, The enhanced activity of mass-selected PtxGd nanoparticles for oxygen electroreduction, Journal of Catalysis, 328 (2015) 297-307.

V. Perazzolo, C. Durante, R. Pilot, A. Paduano, J. Zheng, G.A. Rizzi, A. Martucci, G. Granozzi, A. Gennaro, Nitrogen and sulfur doped mesoporous carbon as metal-free electrocatalysts for the in situ production of hydrogen peroxide, Carbon, 95 (2015) 949-963.

Y. Luo, J.M. Mora-Hernández, L.A. Estudillo-Wong, E.M. Arce-Estrada, N. Alonso-Vante, Nanostructured palladium tailored via carbonyl chemical route towards oxygen reduction reaction, Electrochimica Acta, 173 (2015) 771–778.

B. Wickman, M. Fredriksson, L. Feng, N. Lindahl, J. Hagberg, C. Langhammer, Depth probing of the hydride formation process in thin Pd films by combined electrochemistry and fiber optics-based in situ UV/vis spectroscopy,, Physical Chemistry Chemical Physics, 17 (2015) 18953-18960.

M. Favaro, G.A. Rizzi, S. Nappini, E. Magnano, F. Bondino, S. Agnoli and G. Granozzi, A synchrotron-based spectroscopic study of the electronic structure of N-doped HOPG and PdY/N-doped HOPG, Surface Science, 646 (2016) 132-139.

V. Tripkovic, J. Zheng, G.A. Rizzi, C. Marega, C. Durante, J. Rossmeisl, G. Granozzi, Comparison between the Oxygen Reduction Reaction Activity of Pd5Ce and Pt5Ce: The Importance of Crystal Structure, ACS Catalysis, 5 (2015) 6032-6040.

W. Ju, R. Valiollahi, R. Ojani, O. Schneider , U. Stimming, The Electrooxidation of Formic Acid on Pd Nanoparticles: an Investigation of Size-Dependent Performance, Electrocatalysis, 7 (2016) 149-158.

V. Perazzolo, E. Grądzka, C. Durante, R. Pilot, N. Vicentini, G.A. Rizzi, G. Granozzi, A. Gennaro, Chemical and Electrochemical Stability of Nitrogen and Sulphur Doped Mesoporous Carbons, Electrochimica Acta, (2016) accepted.

L.A. Estudillo-Wong, Y. Luo, J.A. Díaz-Real, N. Alonso-Vante, Enhanced oxygen reduction reaction stability on platinum nanoparticles photo-deposited onto oxide-carbon composites, Applied Catalysis B: Environmental, 187 (2016) 291-300.

Y. Luo, L. Calvillo, C. Daiguebonne, M.K. Daletou, G. Granozzi, N. Alonso-Vante A highly efficient and stable oxygen reduction reaction on Pt/CeOx/C electrocatalyst obtained via a sacrificial precursor based on a metal-organic framework, Applied Catalysis B: Environmental, 189 (2016) 39-50.

Y. Luo, L. A. Estudillo-Wong, L. Cavillo, G. Granozzi, N. Alonso-Vante An easy and cheap chemical route using a MOF precursor to prepare Pd–Cu electrocatalyst for efficient energy conversion cathodes, Journal of Catalysis, 338 (2016) 135–142.

M. Escudero-Escribano, P. Malacrida, M.H. Hansen, U.G. Vej-Hansen, A. Velázquez-Palenzuela, V. Tripkovic, J. Schiøtz, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction, Science, 352 (2016) 73-76.

Proceedings Contributions

J. Ma, L. Seidl, W. Ju, E. Mostafa, L. Asen, S. Martens, U. Stimming and O. Schneider, Applications of Ionic Liquids in Electrochemical Energy Conversion and Storage, ECS Transactions, 64(4) (2014) 407-423.

M.U. Sreekuttan, J.M. Mora-Hernandez, Y. Luo, and N. Alonso-Vante, Substrate Effects on the Catalytic Center of CoSe2 for Oxygen Reduction Reaction, ECS Transactions, 64(36) (2015) 1-9.

Subcategories