Aller au menu Aller au contenu

> Equipes > EIP > Réactivité de surface

Réactivité de surface

Pour la réactivité des surfaces, nous couvrons un champ complet partant des surfaces monocristallines jusqu’aux assemblages membrane/électrodes (AME), via les nanocatalyseurs de forme, structure, chimie et densité de défauts parfaitement contrôlées, en passant par le choix des supports conducteurs électroniques et de porosité adaptée à l’insertion de ionomère et aux phénomènes de transport de matière.
Pour les électrodes monocristallines, nous développons de nouvelles méthodes de caractérisation in situ : la diffraction X résonnante (surface resonant X-ray diffraction: SRXRD) ; synchrotron) et la spectroscopie Raman amplifiée (TERS) par pointe pour caractériser les liaisons avec les adsorbats (nous traiterons notamment le cas de l’adsorption/électrooxydation de monoxyde de carbone sur surfaces nobles).
Pour les nanocatalyseurs, nous souhaitons coupler les équipements DEMS et ICP-MS pour déterminer le rendement faradique des réactions électrocatalytiques prenant place dans les PEMFC et PEMWE (fraction du courant servant efficacement à la réaction électrochimique de dégagement gazeux vs. courant de dissolution des matériaux d’électrodes). Nous commencerons par des électrodes modèles puis étendrons notre approche aux électrocatalyseurs nanostructurés (supportés ou non) et aux systèmes complets.
Pour permettre la fabrication d’AME et leurs tests en cellules complètes, nous mettrons à l’échelle les méthodes de synthèse de nanocatalyseurs développées lors du dernier quinquennal et souhaitons créer une équipe commune avec le CEA-Liten à Grenoble (qui a l’expertise de la mise à l’échelle des matériaux, la fabrication d’AME et leurs tests en cellules élémentaires mais aussi en modules de plusieurs cellules de pile à combustible et d’électrolyseur basse température). Nous appliquerons cette méthodologie aux milieux acide et alcalin pour comprendre et limiter la dégradation des matériaux tout en réduisant les quantités de métal précieux utilisées dans ces dispositifs.

Proton-Exchange Membrane Water Electrolysers (Contact: Frédéric Maillard)

H2 can be produced from water electrolysis in alkaline, neutral or acid electrolytes, and each system has its own advantages and drawbacks. At high pH, the Nernst potential of the oxygen evolution reaction (OER) is considerably lowered, which enables to use non-noble metals (KOH electrolysers use nickel and stainless steel electrodes). However, alkaline electrolytes are highly corrosive, easily poisoned by carbon dioxide, and feature low ion conductivity. Water electrolysers operating with an acid solid polymer electrolyte – also referred to as polymer electrolyte membrane (PEM) water electrolysers (PEMWE) – feature several advantages compared to alkaline electrolyzers: (i) larger energy efficiency at high current density, (ii) versatility (PEMWE may be adapted to different working regimes), (iii) faster start-up, (iv) use of similar polymer electrolyte technology than in PEMFC, for which considerable advances have been obtained during the last decade.

In the frame of the MOISE project, we aim at developing IrOx nanoparticles with enhanced mass activity towards the OER and identical stability as larger rutile-type IrO2 particles in acidic electrolyte. Synthesizing nanometre-sized catalytic materials also requires developing electron-conducting supports that feature (i) a large specific surface area to maximize the distribution of the nanoparticles while preventing their agglomeration/aggregation, (ii) an optimal pore size distribution to allow easy access of reactants to the electrode and products removal from the electrode. Equally important, the catalyst support should be able to withstand high electrochemical potential (E > 1.8 V vs. the standard hydrogen electrode - SHE), highly acidic environment and moderate temperature (< 80-90 °C). These operating conditions render classical high surface area supports, such as carbon blacks, unstable (carbon is oxidized at potentials above 0.207 V vs. SHE). We thus focus on conductive metal oxides like doped tin dioxide, the morphology of which is amenable to the specifications of PEM water electrolysis. Moreover, their electronic conductivity can be tuned by changing the nature and concentration of the doping element. To know more about this.

Alkaline Water Electrolysers (Contact: Marian Chatenet and Jonathan Deseure)

Proton Exchange Membrane Fuel Cells (Contact: Laetitia Dubau and Frédéric Maillard)

PEMFC, thanks to their potentially unlimited energy density, are progressively implemented in new portable, automotive or remote stationary devices. However, several hurdles remain before their widespread commercialization: (i) improving the rate of the cathode reaction (the oxygen reduction reaction, ORR) kinetics, (ii) decreasing the cost of the catalytic layers, (iii) improving the durability of the cathode material and (iv) efficiently transfering highly-active ORR nanocatalysts from ‘beaker’ cells (cells made of glass and filled with liquid electrolyte classically used in academic laboratories) to real MEAs.

In the BRIDGE project, we thus aim at identifying and unlocking obstacles limiting the implementation of promising ORR catalyst materials, identified after fundamental and model investigations in well-controlled laboratory conditions, into efficient PEMFC cathodes. To this goal, a library of materials composed of state-of-the-art ORR nanocatalysts (octahedral, cubic, hollow, nanowires and spongy) is currently built, and the synthesis processes will be scaled-up in a stepwise manner to reach volumetric quantities allowing membrane electrode assemblies manufacturing.To know more about this.

In the CAT2CAT and ANIMA projects, we work on alternative to Pt such as Metal-nitrogen-carbon catalysts (Metal-N-C with Metal = iron or cobalt). Such materials often comprise different types of nitrogen groups and metal species, from atomically dispersed metal-ions coordinated to nitrogen (Metal-NxCy), to metallic or metal-carbide particles (Metal@N-C), partially or completely embedded in graphene shells. While disentangling the different contributions of these species to the initial ORR activity of Metal-N-C catalysts with multidunous active sites is complex, following the fate of these different active sites during electrochemical ageing is even more difficult. To this goal, samples differing from each other by the nature of the metal (Fe or Co), the metal content and the heating mode applied during pyrolysis have been synthesized. All catalysts showed high beginning-of-life ORR mass activity but are prone to age differently in PEMFC operating conditions. To know more about this.

Direct Alkaline Fuel Cells (Contact: Marian Chatenet)

Alkaline fuel cells (AFC) enable to use non-carbon fuels in substitute to hydrogen and non-Pt electrocatalysts without performance losses. The team of interfacial electrochemistry and processes addresses the topic of AFC by focusing on two aspects: (1) materials and mechanisms of electrooxidation of non-carbon fuels of the boron and nitrogen families (for direct AFC) and (2) non-Pt electrocatalysts for the oxygen reduction reaction (ORR). To know more about this.

Réactivité à la surface des monocristaux (Contact: Eric Sibert)

La réactivité en catalyse hétérogène et en particulier en électrocatalyse est très sensible à la structure de surface. Pour relier la réactivité et la structure de la surface, il est indispensable de travailler sur des surfaces bien définies à l'échelle atomique. Les électrodes monocristallines, pour lesquelles une seule orientation cristallographique peut être mise en contact avec l'électrolyte, représentent un catalyseur modèle très intéressant pour l'étude de l'orientation cristallographique sur l'activité catalytique.
Plus de détails sur les études avec des méthodes classiques et celles utilisant le rayonnement synchrotron.

Metal-Air Batteries (Contact: Marian Chatenet)

Metal-air batteries also are electrochemical generators of large energy density. We recently started to work on Li-air batteries, in industrial collaborations. With EDF, we tackled the issues of the oxygen electrode in aqueous Li-air batteries. With Hutchinson, we are presently working on the ORR/OER mechanisms in non-aqueous electrolytes, a topic in which we initiated a collaboration with Northeastern University (Sanjeev Mukerjee, USA). To know more about this.

mise à jour le 3 décembre 2019

Univ. Grenoble Alpes