Molecular dynamics simulations of ternary PtxPdyAuz fuel cell nanocatalyst growth

International audienceMolecular dynamics simulation of PEMFC cathodes based on ternary Pt70Pd15Au15 and Pt50Pd25Au25 nanocatalysts dispersed on carbon indicate systematic Au segregation from the particle bulk to the surface, leading to an Au layer coating the cluster surface and to the spontaneous formation of a Pt@Pd@Au core-shell structure. For Au content below 25at%, surface Ptx Pdy active sites are available for efficient oxygen reduction reaction, in agreement with DFT calculations and experimental data. Simulations of direct core@shell system prepared in conditions mimicking those of plasma sputtering deposition pointed out an increase of the number of accessible PtxPd y surface active sites. Core-shell nanocatalyst morphology changes occur due to impinging Pt kinetic energy confinement and dissipation

Synthesis, characterization and evaluation of electrocatalytic multimetallics electrocacatalysts for the oxygen reduction reaction at the cathode of the PEMFC

Ce travail a porté sur l'élaboration de matériaux plurimétalliques et l'étude de leurs propriétés électrocatalytiques. Les matériaux monométalliques (Pt/C, Pd/C, Au/C), bimétalliques à base de métaux nobles (PtxAu1 x/C, PtxPd1 x/C et PdxAu1 x/C) et non nobles (PtxNi1 x/C, PtxCo1 x/C et PtxCu1 x/C) ont été dans un premier temps synthétisés par la méthode microémulsion « water-in-oil ». Une attention particulière a été portée sur les caractérisations physicochimiques et électrochimiques des matériaux synthétisés afin d'accéder à leur microstructure, la taille moyenne de leurs particules, leur morphologie, leur taux de charge sur le support carboné ou encore la composition atomique de volume et de surface de leurs nanoparticules. Leurs propriétés électrocatalytiques et leur sélectivité pour la réaction de réduction du dioxygène ont été étudiées en milieu HClO4 0,1 M à l'aide d'une électrode à disque tournant. Il a été montré que l'ajout du palladium ou du l'or au platine conduit à une diminution progressive de l'activité catalytique à l'exception du catalyseur Pt90Au10/C. Les catalyseurs PdxAu1 x/C ont montré de faibles activités catalytiques avec l'ajout de l'or. En revanche, les catalyseurs bimétalliques PtxNi1 x/C et PtxCo1 x/C ont montré une amélioration de l'activité électrocatalytique par rapport au platine pur. L'addition du cuivre au platine (PtxCu1 x/C) a permis une légère améliorer l'activité électrocatalytique sur un intervalle de potentiel compris entre 1,05 et 0,93 V / ERH. Tous les catalyseurs ont montré une sélectivité pour la formation de l'eau à l'exception des catalyseurs PtxAu1 x/C et PdxAu1 x/C qui ont montré une sélectivité pour la formation du péroxyde d'hydrogène lorsque la teneur en or devient importante. A partir des résultats obtenus sur les catalyseurs bimétalliques, une formulation des matériaux trimétalliques (PtxMyAuz/C, M= Co, Cu, Ni, Pd) a été réalisée. Ensuite, les propriétés physicochimiques et électrochimiques de ces matériaux ont été étudiées. Les propriétés catalytiques de ces matériaux ont été étudiées. Il en ressort que le catalyseur Pt60Ni20Au20/C conduit à l'activité maximale. Tous ces catalyseurs ont montré une sélectivité pour la formation de l'eau. L'étude de stabilité par cyclage potentiométrique sur les catalyseurs trimétalliques a révélé que le catalyseur Pt60Cu20Au20/C présente une meilleure stabilité que le platine et les autres catalyseurs trimétalliques. Une ségrégation de l'or en surface a été observée sur les matériaux après cyclage potentiométrique.This work has focused on the development of polymetallic catalysts and study of their electrocatalytic properties. The monometallics catalysts (Pt/C, Pd/C and Au/C) and the binary catalysts based on noble metals (PtxAu1 x/C, PtxPd1 x/C and PdxAu1 x/C) and non-noble metals (PtxNi1 x/C, PtxCo1 x/C and PtxCu1 x/C) have been synthesized using the « water-in-oil » microemulsion method. Investigation of the physicochemical and the electrochemical characterization of the synthesized materials has been conducted in details to findout their microstructure, their average particles sizes, their morphology, their metal loading on the carbon support or their bulk and the surface composition of their nanoparticles. The electrocatalytic properties and the selectivity toward the oxygen reduction reaction of these catalysts have been studied using a rotating disc electrode in 0.1 M aqueous HClO4 saturated with oxygen. The results demonstrate that the addition of palladium or gold to platinum (PtxAu1 x/C and PtxPd1 x/C) led to the constant decrease of the electroalalytic activity with an increase of Pd or Au ratio, except for the Pt90Au10/C. The PdxAu1-x /C catalysts showed low catalytic activity with the addition of gold. However, the bimetallic catalysts PtxNi1-x/C and PtxCo1-x/C showed improved electrocatalytic activities compare with pure platinum. The addition of copper to the platinum (PtxCu1-x/C) resulted in a slight increase of the electrocatalytic activity on a potential range between 1.05 and 0.93 V vs. RHE. All catalysts have shown selectivity for water formation except PtxAu1-x/C and PdxAu1-x/C catalysts, which showed selectivity for the formation of hydrogen peroxide by increasing of gold content. According to the results obtained from the binary catalysts, ternary catalysts (PtxMyAuz/C, M = Co, Cu, Ni, Pd) were made. The physicochemical and the electrochemical properties of these catalysts have been studied. The study of the catalytic activity of these catalysts showed that the best activity is obtained Pt60Ni20Au20/C. All of these catalysts have showed selectivity for water formation. The ageing tests have been carried out by conducting potentiometric cycling, showing that Pt60Cu20Au20/C catalyst has a better stability than the platinum and the other trimetallic catalysts. The gold segregation from the bulk to the surface of nanoparticles was observed on these catalysts, after potentiometric cycling

Electrocatalytic behaviour towards oxygen reduction reaction of carbon-supported Pt x M y Au z (M = Ni, Cu, Co) binary and ternary catalysts

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Oxygen reduction reaction at binary and ternary nanocatalysts based on Pt, Pd and Au

International audienceCarbon-supported monometallic, binary and ternary nanocatalysts based on Pt, Pd and Au were synthesized by a "water in oil" microemulsion method and characterized by atomic absorption spectrometry, thermogravimetry, transmission electron microscopy, X-ray diffraction, and electrochemical methods. A comparative study of the oxygen reduction reaction on monometallic, alloyed binary and ternary nanocatalysts has been performed. The catalytic activity and the selectivity of the nanocatalysts towards the ORR have been determined by rotating disc electrode and rotating ring disc electrode in O-2-saturated 0.1 M HClO4 electrolyte. It was shown that the addition of palladium to platinum led to a constant decrease of the activity with the Pd ratio. The modification of platinum by gold allows improving the activity of the catalyst towards ORR for gold ratio up to 50 at%. Ternary Pt70Pd15Au15/C and Pt50Pd25Au25/C were synthesized. These catalysts showed improved catalytic activities towards ORR. Aging tests have been carried out, showing that a part of the loss in the activity of gold containing catalysts is due to gold segregation from the bulk to the surface of nanoparticles

Oxygen Reduction Reaction at Binary and Ternary Nanocatalysts Based on Pt, Ni and Au

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Direct electrochemistry of cytochrome bo3 oxidase at a series of gold nanoparticles-modified electrodes

New membrane-protein based electrodes were prepared incorporating cytochrome bo3 from Escherichiacoli and gold nanoparticles. Direct electron transfer between the electrode and the immobilized enzymes was achieved, resulting in an electrocatalytic activity in presence of O2. The size of the gold nanoparticles was shown to be important and smaller particles were shown to reduce the overpotential of the process. Keywords: Membrane protein, Gold nanoparticles, Direct electron transfer, Electrocatalysi

Overview of SMARTCAT - Systematic, Material-oriented Approach using Rational design to develop break-Through Catalyst s for commercial automotive PEMFC

Communication oraleInternational audienceIn frame of SMARTCat project, the consortium will build a new concept of electrodes based on new catalyst design(ternary alloyed/core-shell clusters) deposited on a new high temperature operation efficient support.In order to enhance the fundamental understanding and determine the optimal composition and geometry of theclusters, advanced computational techniques will be used in direct combination with electrochemical analysis of theprepared catalysts. The use of deposition by plasma sputtering on alternative non-carbon support materials willensure the reproducible properties of the catalytic layers. Plasma technology is now a well established, robust,clean, and economical process for thin film technologies.Well-defined chemical synthesis methods will also be used prior for defining the best catalysts. In addition, MEApreparation, testing, and MEA automated fabrication will complete the new concepts of catalysts with aconsiderably lowered Pt content (below 0.01 mgcm-2 and as low as 0.001 mgcm-2) and alternative support. The finalgoal will be to deliver a competitive and industrially scalable new design of PEMFC suitable for automotiveapplications.SMARTCat address the following objectives:• Deliver specifications/requirements for reaching the technical goals as a roadmap.• Design new efficient catalyst architecture• Establish a support selection criterion based on physico-chemical characterization and modelling for definingthe most suited electrode support to the defined catalytic system• Assess the robustness regarding operation conditions and fuel cell efficiency• Enable to automate the MEA production using state of the art (< 100°C) and high temperature membranes(120°C)• Build efficient short-stack required for competitive automotive fuel cell operation• Low cost process and low Pt content will dramatically reduce the fuel cell cost, and which will lead toeconomically suitable fuel cells for automotive applicationAmong the main findings, up-to-date SMARTCat major outputs are:1. The results regarding the best tri-metallic catalysts obtained by a combined experiment-theory common work.In this context PtPdAu tri-metallic catalysts have been evaluated. It has been found that contrary to theliterature, this system has the drawback to allow Au migration on the surface, when concentration is higherthan 25%. Thus, this will reduce the ORR activity. Consequently reducing Pt noble catalyst content will bedifficult. PtNiAu are thus preferred in the present time and are further investigated.2. Tin Oxide (SnO2) does not have sufficient electronic conductivity, and must therefore be modified. Theproperties of this material was tailored by (i) different doping (e.g. niobium (Nb), antimony (Sb)) to achievesufficient n-type electronic conductivity, (ii) different synthesis techniques to tailor the particle size, surfacearea and pore size distribution of the support materials. Two different techniques (co-precipitation and flamespray pyrolysis) with preferable potential to be up scaled are used. In parallel, theoretical research has beenfocused on (i) identification of the correct model system for the SnO2/Pt interface and the correctcomputational setup for the description of its electronic structure, (ii) the computational modelling of theinterface between Pt(111) and SnO2(110) and the role of migration and localization of Sb in SnO2at thisinterface, (iii) segregation of the doping elements (Sb and Nb) at the SnO2/Pt interface, and (iv) the study of theinfluence of segregation on the transport properties of the whole system.3. High temperature polymer membrane is currently developed within the project. Monomer, polymer synthesis iswell in hand (a 1 kg campaign), thin unreinforced film preparation and curing at lab scale (100 – 150 cm2)proceeds well; membrane activation with acid is not yet under satisfactory control