BRIDging the environment(al) Gap: promising catalyst materials to performant fuel cells Electrodes – BRIDGE

A library of materials composed of state-of-the-art shape-selected (octahedral, cubic, hollow, nanowires and spongy) ORR catalysts will be built (Task 1), and the synthesis processes will be scaled-up in a stepwise manner to reach volumetric quantities allowing MEAs manufacturing. In Task 2, the structure and the chemistry of these catalysts and the ionomer content and distribution within the cathode structure will be determined at each step of the MEA manufacturing to rationalize their performance in real PEMFC systems (Task 5). The changes of the catalyst’s performance in the kinetic region of the polarization curve (where metal content, structure, chemistry and dispersion play pivotal roles) but also in the mass-transport region (where ionomer chemistry, content and distribution as well as porosity within the volume of the electrode play pivotal role) will be rationalized using a specific diagnostic toolbox, combining advanced experimental measurements and modelling, (Task 4). This task will loop with Task 3 to adapt the ink formulation from which the MEAs will be manufactured (catalyst content, structure and chemistry, ionomer content and chemistry, use of additives and solvent composition). Outputs of Task 4 will be strategies to mitigate issues related to low density of catalytic sites (shape-selected ORR catalysts usually feature large crystallite size), incomplete wetting of the catalyst by the ionomer and poor accessibility for O2 to the catalytic sites and thus ensure good PEMFC performances at high current densities. ASTs will also be carried out in Task 5 and Task 4: after characterisation (Task 2), the results of these tests will help rationalizing why the degradation mechanisms might be different in simulated and real PEMFC operating conditions.

The scale-up of the advanced cathode catalyst materials syntheses to reach the sufficient amount necessary for catalyst-coated membrane (CCM) preparation and further tests in fuel cell conditions at the single cell level has been achieved for spongy catalysts.
Specific works on the catalyst-ink formulation for CCM preparation is carried out at the ZSW.
The LEPMI developed a specifically designed a single cell for in situ synchrotron studies. A first campaign of measurements took place at the ESRF and preliminary results are obtained on the library of material up-scaled. MEA were prepared by SYMBIO.
The development of the Gas Diffusion Electrode technique has been initiated at the LEPMI.

Works are currently carried out at adapting the synthesis procedure for PtNi octahedra and their preparation at the gram-scale level will require either a full revision of the synthesis protocol or even a complete change of the synthesis strategy. Monitoring of the progresses in the synthesis works are fully supported by the physical-chemical characterisations.
Preliminary results of synchrotron measurements indicate that potential changes in the crystallite size and the global strain (PtNi degree of alloying) of the catalyst materials embedded in the CCM can be tracked confidently, while issues associated with the parallax complicate the extraction of the microstrain to further estimate the nanocrystal lattice distortions descriptor. Mitigation strategies are under development.
The development of the Gas Diffusion Electrode technique is currently in progress at LEPMI.

1. R. Chattot, P. Bordet, I. Martens, J. Drnec, L. Dubau, F. Maillard, “Building Practical Descriptors for Defect Engineering of Electrocatalytic Materials”, invited Viewpoint Article, ACS Catal. 10 (2020) 9046-9056. DOI: 10.1021/acscatal.0c02144

2. Martens, R. Chattot, T. Wiegmann, T. Fuchs, O. M. Magnussen, L. Dubau, F. Maillard, J. Drnec, “Towards Comprehensive Understanding of Proton-Exchange Membrane Fuel Cells Using High Energy X-rays”, J. Phys. Energy (2021) invited article. DOI: 10.1088/2515-7655/abf43d

Emission-free transport is a fundamental pillar for the energy transition towards a green energy landscape. Proton Exchange Membrane Fuel Cells (PEMFCs), using hydrogen (H2) and oxygen (O2), are at the forefront of the portfolio of practical solutions that are emerging on the market. However, Europe, and a fortiori France and Germany, has to develop a strategic positioning for research and development to maintain in-house the manufacturing of advanced and strategic technologies involved in the energy transition and thus preserve its independence; unlike as, e.g., batteries and solar panels production in spite of large investments. The present project proposal aims at identifying and unlocking obstacles limiting the implementation of promising O2 reduction reaction (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) will be built, and the synthesis processes will be scaled-up in a stepwise manner to reach volumetric quantities allowing MEAs manufacturing. The (i) structure and the chemistry of these nanocatalysts and (ii) the ionomer content and distribution within the cathode structure will be determined at each step of the membrane-electrodes assembly (MEA) manufacturing to rationalize changes of performance in model and real PEMFC systems. A specific diagnostic toolbox, combining advanced experimental techniques and modelling, will be specifically developed and the output of this toolbox will be used to adapt the ink formulation from which the MEAs are manufactured (catalyst content and chemistry, ionomer content and chemistry, solvent composition, use of additives). Strategies to mitigate issues related to low density of catalytic sites (highly-active ORR nanocatalysts usually feature large crystallite size), incomplete wetting of the catalyst by the ionomer and poor accessibility for O2 to the catalytic sites will be also developed. Finally, accelerated stress tests (ASTs) will be carried out. After characterisation, the results of these tests will help rationalizing why the degradation mechanisms may be different in simulated and real PEMFC operating conditions. Ultimately, the key findings of the project will be transferred to Heraeus and Symbio for industrial development. The ambitious research program proposed in the frame of the BRIDGE project requires efforts of scientific teams with broad interdisciplinary expertise in chemistry and physics, materials science and engineering. Therefore, this proposal brings together two groups at LEPMI/CNRS and ZSW, and two industrial partners Heraeus and Symbio. LEPMI/CNRS will use its expertise in the synthesis of ORR nanocatalysts and electrocatalysis using model electrodes to understand the structural, compositional and morphological changes occurring during elaboration of MEAs, while the ZSW group will engineer them to implement them in real-life PEMFC. The two industrial partners, Heraeus and Symbio, are a well-established catalyst materials manufacturer and an automotive equipment supplier designing and developing a large range of PEMFC related products, from specifically designed MEAs to a few hundreds kW systems, for electric vehicles, respectively. The BRIDGE project thus covers all the facets of a critical technology that is expected to grow further for the development of independent European-based solutions in the field of sustainable energy transition. It also intends to setup solid foundations for future original contributions from the French-German consortium in the field of PEMFCs electrodes technology/concepts, and its transfer towards the European industry.