LEPMI - Rubrique EIP Physicochimie 2022

Surface reactivity

For surface reactivity, we cover a complete field from single crystal surfaces to membrane/electrode assemblies (MEAs), via nanocatalysts with perfectly controlled shape, structure, chemistry and defect density, as well as the choice of electronic conductive and porous supports adapted to ionomer insertion and material transport phenomena.

For single crystal electrodes, we are developping new in situ characterization methods: SRXRD: surface resonant X-ray diffraction (synchrotron) and tip-enhanced Raman spectroscopy (TERS) to characterize the bonds with adsorbates (we will treat in particular the case of carbon monoxide adsorption/electrooxidation on noble surfaces).

For nanocatalysts, we wish to couple the DEMS and ICP-MS equipments to determine the faradic efficiency of the electrocatalytic reactions taking place in PEMFCs and PEMWEs (fraction of the current effectively used for the electrochemical reaction of gas emission vs. dissolution current of electrode materials). We will start with model electrodes and then extend our approach to nanostructured electrocatalysts (supported or not) and complete systems.

To enable the manufacture of AMEs and their tests in complete cells, we will scale up the nanocatalyst synthesis methods developed during the last five years and wish to create a joint team with CEA-Liten in Grenoble (which has expertise in scaling materials, manufacturing AMEs and their tests in elementary cells but also in modules of several fuel cell and low-temperature electrolyzer cells). We will apply this methodology to acid and alkaline environments to understand and limit material degradation while reducing the amount of precious metal used in these devices.

Proton-exchange membrane water electrolysers and alkaline water electrolysers

Proton-Exchange Membrane Water Electrolysers (Contact: Frédéric Maillard) and
Alkaline Water Electrolysers (Contact: Marian Chatenet and Jonathan Deseure)

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 framework of the Hy-walHy project, we are studying an original way of intensifying the process by magnetic activation. This greatly reduces electrode overvoltages and makes the process more compatible with intermittent operation, without the use of noble metals at the electrodes. We are also studying steel electrodes for the release of oxygen in an alkaline environment, as these electrodes are both highly active and durable.

Water electrolyzers operating with an acidic solid polymer electrolyte - also called polymer electrolyte membrane water electrolyzers (PEMWE) - have several advantages over alkaline electrolyzers : (i) higher energy efficiency at high current densities, (ii) versatility (PEMWE water electrolyzers can operate in a variety of regimes), (iii) faster start-up, (iv) use of polymer electrolyte technology similar to PEMFC technology, for which considerable improvements have been made over the past 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.

Finally, in addition to the dihydrogen evolution reaction, we are also investigating the insertion of atomic hydrogen into materials, which can be another type of storage. The European project HERMES aims to explore the insertion of hydrogen and deuterium into palladium. LEPMI will be in charge, firstly, of the synthesis of Pd nanoarticules with specific forms and, secondly, of their physical and chemical characterisation, including the determination of electrochemical insertion isotherms of H and D.

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.

The european project ALPE aims at developing and commercializing a proton-exchange membrane fuel cell (PEMFC) power plant yielding 5 kW, a durability of 5000 hours, and including 0.5 g of Pt instead of 1 g or more. This is achieved with radically new hierarchical nanostructured electrocatalysts (ECs) promoting the electrochemical processes of the PEMFC. ALPE covers the value chain from the ECs to the assembly and validation of the PEMFC power plant. To know more bout this.

The PEPR-H2 PEMFC95 project aims to meet the needs of heavy mobility (trains, trucks, buses), which requires PEMFCs capable of delivering higher power than current systems, while being more durable and less expensive. The project aims to meet these objectives by developing PEMFCs that can operate at a stabilised temperature of 95°C. 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

Reactivity on single crystal surfaces

Contact: Eric Sibert

The reactivity in heterogeneous catalysis and especially in electrocatalysis is very sensitive to the surface structure. To bridge surface reactivity and structure, it is mandatory to work on well-defined surfaces. Single crystal electrodes, for which a single orientation can be put in contact with the electrolyte, represent a very interesting model catalyst for the study of the crystallographic orientation on catalytic activity. More details on classical electrochemical investigation and synchrotron related measurements.

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.