Arenz, M.

Crampton, A. S.

Deiana, Davide

Heiz, U.

Nesselberger, M.

Ridge, C. J.

Röefzaad, M.

Schweinberger, F. F.

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 20, 2017Fuel Cell Catalyst degradation mechanismsa study on well defined Platinum Nano-ClustersRöefzaad, M.; Nesselberger, M.; Deiana, Davide; Schweinberger, F. F.; Crampton, A. S. ; Ridge, C. J. ;Heiz, U.; Arenz, M.Publication date:2012Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Röefzaad, M., Nesselberger, M., Deiana, D., Schweinberger, F. F., Crampton, A. S., Ridge, C. J., ... Arenz, M.(2012). Fuel Cell Catalyst degradation mechanisms: a study on well defined Platinum Nano-Clusters. Postersession presented at 3rd CARISMA International Conference on Medium and High Temperature ProtonExchange Membrane Fuel Cells, Copenhagen, Denmark.F A C U L T Y   O F   S C I E N C E U N I V E R S I T Y   O F  C O P E N H A G E N  0 0.001 0.002 0.003 0.004 0.005 0.0 0.5 0.7 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.7 1.8 1.9 2.0 2.0 2.1 2.1 2.2 2.3 2.3 2.4 2.4 2.5 2.5 2.6 2.6 2.7 2.7 2.8 2.8 2.9 2.9 2.9 3.0 count per nm2 diameter (nm) Square Waves Fuel Cell Catalyst degradation mechanisms a study on well defined Platinum Nano-Clusters M. Röefzaada, M. Nesselbergera, D. Dieanab, F.F. Schweinbergerc, A.S. Cramptonc, C.J. Ridgec, U. Heizc, M. Arenza m.arenz@chem.ku.dk Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen References: [1] U. Heiz, et. al, Rev. Sci. Instrum, 1997, 68, 1986. [2] S. Torquato, B. Lu, J. Rubinstein, Phys. Rev. A, 1990, 41, 2059. [3] C.G. Granqvist, R.a. Buhrman, J. Catalysis, 1976, 42, 477. Acknowledgements: This work was supported by the Danish DFF through grant # 10-081337 Experimental Setup Deposition of Pt cluster catalyst under UHV. [1] • Synthesis by laser      evaporation  • Mass selection by QMS  • Deposition under     softlanding conditions    onto TEM-Grids (Scanning) Transmission                      Electron Microscopy • Particle structure and size • Dispersion on the carbon support  • three electrode setup with home build all-Teflon electrochemical cells. • the measurements are automated using in-house written Labview software controlling the RDE, gas changers and a home build potentiostat.  Accelerated degradation tests RE CE WE gas inlet Particle Detachment Platinum Dissolution Particle Coalescence a) b) c) Decrease in number Decrease in  particle size Moving and  particle size growth 2 D Model system: easier to study & without the influence of the support One of the main fundamental problems of polymer electrolyte membrane fuel cells (PEMFCs) to date is a low practical  efficiency, due to the degradation of the catalyst in a fuel cell during operation. Especially to clarify the ongoing processes and the responsible factors for the degradation and therefore the loss of usable catalytic active material, is one important step to achieve long term stability of PEMFCs. In this study we used Pt-Nanoclusters (NCs) supported on TEM gold grids as a model system for Fuel Cell Catalysts to address the widely discussed mechanisms of Fuel Cell Catalyst degradation. Accelerated aging tests with different potential profiles are used to study the main responsible degradation mechanism. Particle Distribution Initial Sample 0.4 – 0.6 V 0.4 – 0.8 V 0.4 – 1.0 V Initial Sample 500 mV/s 250 mV/s 50 mV/s 1 2,7182802468101214161 2,7182824681012141 2,718280246810121 2,71828246810120,4 - 0,8 V 0,4 - 1,0 V0,4 - 0,6 V count (% of total)before DEGtest    count (% of total)diameter (nm) diameter (nm) experimental count           simulated Gauß-distribution0 0.002 0.004 0.006 0.008 0.00 0.71 1.01 1.24 1.43 1.60 1.75 1.89 2.02 2.14 2.26 2.37 2.47 2.57 2.67 2.76 2.85 2.94 count per nm2 diameter (nm) Initial Sample Triangular Waves Square Waves 2e2Pt 1 2,7182802468101214161 2,718282468101214161 2,718280246810121416182022241 2,7182824681012141618202224  count (% of total)initial Sample   500 mV/s250 mV/scount (% of total)diameter (nm)  50 mV/sdiameter (nm) experimental count      simulated Gauß-distribution• STEM images were taken from the cluster samples before and after accelerated     aging tests. • Statistical analysis of the nearest neighbour distribution shows clear differences in the    nanocluster distribution on the carbon film.    Initial Sample – the cumulative probability of the clusters (red line) is in good agreement                             with the  theoretical curve assuming a random distribution (gray dashed                            line) [2]  (red colored region displays a statistical significance of 5%)   after Degradation-test - the NN distance distribution after 3000 Square Waves (0.4 – 1.0 V,                             3s:3s) or 4 hours triangular waves (0.4 – 1.0 V, 250 mV/s) deviates                            in the region of 2 – 3.5 times the average nanocluster diameter from the                            theoretical curve.    • Clusters moved during the aging tests • loss of random distribution • favoured distance between 2 and 3.5 times the average diameter  Square Waves Particle size distribution depending on the potential window:  • total number of particles decreases significantly when using the largest potential   window, while the range of cluster sizes stays constant             - high losses especially for smaller particles • no growth of particles could be detected  • the shape of the particle size distribution stays unchanged before and after the    aging tests, independent from the potential window          - The log-normal distribution of the cluster diameters (red curve) shows for all            samples a gaussian (gray line for simulated distribution), indicating the            absence of Ostwald Ripening [3] in case of a square wave potential profile.  Particle size distribution: • no Ostwald Ripening • no coalescence due to agglomeration  Sample Initial Sample 0.4 – 0.6 V 0.4 – 0.8 V 0.4 – 1.0 V Cluster / nm2 0,036 0,031 0,034 0,021 Av. Diameter (nm) 1,33 1,35 1,33 1,46 • most likely simple particle detachment from the support Sample Initial Sample 500 mV/s 250 mV/s 50 mV/s Cluster / nm2 0,036 0,036 0,036 0,029 Av. Diameter (nm) 1,33 1,33 1,15 1,13 Particle size distribution: Triangular Waves Particle size distribution depending on the scan rate:  • total number of particles decreases only slightly when the slowest scan rate is    used, while the average diameter decreases constantly with decreasing scan rate • number of large particles decreases • the size distribution shifts to smaller diameter with a narrow, nearly normal curve   distribution.       - The log-normal distribution of the cluster diameters (red curve) deviates from       the ideal Gaussian curve, particularly at small diameters.   • slow scan rates are most effective • no simple particle detachment but reshaping of the clusters  • no coalescence due to agglomeration  Affiliations:  a  Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen b  Technical University of Denmark,Center for Electron Nanoscopy, 2800 Kongens Lyngby c Technische Universität München, Chair of Physical Chemistry, CRC, Lichtenbergstraße 4, 85748 Garching, Germany. 

Fuel Cell Catalyst degradation mechanisms:a study on well defined Platinum Nano-Clusters

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Fuel Cell Catalyst degradation mechanisms:a study on well defined Platinum Nano-Clusters

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