Promoting Surface Distortion for Improved Fuel Cell Electrocatalysis

International audienceThe electrochemical activation of oxygen is the cornerstone of electrochemical conversion and storage devices, such as fuel cells, metal-air batteries, and electrolysers. It is well established that Pt is the only metal that can catalyse efficiently the oxygen reduction reaction (ORR) in acidic electrolyte, the reaction limiting the performance of low temperature proton-exchange membrane fuel cells (PEMFCs). However, due to the high cost and scarcity of Pt, research efforts recently focused on enhancing simultaneously its intrinsic activity (specific activity i.e. the current produced per cm 2 of Pt) and its mass activity (the current produced per gram of Pt). Studies on Pt or PtNi single crystals have established that the ORR is a structure sensitive reaction, which is best electrocatalyzed on (111) facets in acidic electrolyte. Combining alloying and ensemble effects recently led to 20-30-fold enhancement of the specific activity for the ORR on PtNi/C nanooctahedra relative to Pt/C nanoparticles. However, due to the highly oxidizing conditions of the PEMFC cathode (high electrochemical potential, presence of oxygen, acidic pH), the stability of these "dream" catalysts was found poor in PEMFC cathode operating conditions, thus compromising their utilization in real devices 1. Strikingly, it also turned out recently that alloyed but structurally-disordered nanocatalysts, such as hollow PtNi/C nanoparticles, porous PtNi/C nanoparticles, PtNi aerogels or PtNi nanosponges also feature highly desirable and sustainable ORR activity (x 10-12 in specific activity relative to pure Pt/C). Even more striking, the ORR kinetics depends on the concentration of structural defects: the higher the structural disorder in a given nanocatalyst, the best is its intrinsic activity for the ORR but also other oxidation reactions 2. This talk will address our recent insights about the quantification and the role played by structural defects in heterogeneous electrocatalysis from the beaker cell to the fuel cell device. Our proposal is based on Rietveld refinement of wide angle high energy X-rays scattering measurements and high resolution electron microscopy for a broad range of nanocatalysts combined with density functional theory calculations (DFT) References:C. Cui, L. Gan, M. Heggen, S. Rudi, and P. Strasser, “Compositional segregation in shaped Pt alloynanoparticles and their structural behaviour during electrocatalysis,” Nat. Mater., vol. 12, no. 8, pp. 765–771, 2013.2. R. Chattot, T. Asset, P. Bordet, J. Drnec, L. Dubau, and F. Maillard, “Beyond strain and ligand effects:Microstrain-induced enhancement of the oxygen reduction reaction kinetics on various PtNi/Cnanostructures,” ACS Catal., vol. 7, pp. 398–408, 2017.3. R. Chattot et al., “Surface distortion as a unifying concept and descriptor in oxygen reduction reactionelectrocatalysis,” Nat. Mater., vol. 17, no. September, pp. 827–833, 2018

Electrode à réseau multiple de collecte de courant

L’invention concerne une électrode pour un dispositif rechargeable de stockage de l’énergie, comprenant plusieurs couches de matériau d’électrode et plusieurs couches poreuses de collecteur de courant, lesdites couches de matériau d’électrode et de collecteur de courant étant disposées de façon spécifique, un dispositif rechargeable de stockage de l’énergie comprenant ladite électrode, ainsi que les utilisations de ladite électrode

Distorted Surfaces for Electrocatalysis

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Electrocatalyseurs platine-ruthénium nanodispersés pour une pile à combustion directe de méthanol

Ce travail s'inscrit dans le cadre du développement de catalyseurs nanostructurés actifs pour l'électrooxydation du méthanol. Le platine est indispensable mais engendre une importante limitation cinétique, conséquence de la présence de l'espèce poison COads à sa surface. Associé au platine, le ruthénium diminue cet empoisonnement. La méthode colloïdale a permis de synthétiser deux types de catalyseur platine-ruthénium avec une taille de particules de l'ordre de 2 nm. Le premier, mélange de particules de platine et de ruthénium s'est avéré plus actif pour l'oxydation du CO et du méthanol que le second présentant une structure d'alliage. Le recours à des techniques de spectroscopie +-in situa (DEMS et FTIRS) a permis de mettre en évidence une plus grande sélectivité du mélange pour la production de CO2. La composition optimale a été évaluée à 70:30 pour une température de fonctionnement entre 25 et 50 ʿC. Enfin, des tests en pile à combustible (DMFC) ont permis d'atteindre des densités de puissance de l'ordre de 110 mW/cm2.The aim of this work is the development of nanostructured catalysts active for the electrooxidation of methanol. Platinum is necessary but presents several problems limiting the overall kinetic of the reaction as the consequence of the presence of COads on its surface. Associated to platinum, ruthenium decreases the CO poisoning effect. The colloidal method allows to synthesize two kinds of platinum-ruthenium catalysts with a particle size about 2 nm. The first one is a mixture of platinum and ruthenium particles and is more active for CO and methanol oxidation than the second one which presents an alloy structure. "In situ" spectroscopic techniques permits to understand such a difference in activity, showing a greatest selectivity in the case of the mixture for CO2 production. An optimal composition of 70:30 has been evaluated at a working temperature between 25 and 50ʿC. Finally, real fuel cell tests allows to obtain power density around 110 mW/cm2.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Carbon-capped PtNi-alloy cathodic electrocatalysts for PEMFC

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