Résumé
Green hydrogen has the potential to dramatically reduce our greenhouse gas emissions and achieve the net-zero targets set by many countries by 2050. This hydrogen can be produced by electrolysis using water and renewable electricity, and used later on demand to produce electricity with fuel cells, for a broad range of applications. However due to their acidic environment, the present generation of proton exchange membrane fuel cells (PEMFC) requires precious metal catalysts, in particular platinum, which is an obstacle to their large-scale deployment. In contrast, anion exchange membrane fuel cells (AEMFCs) operate at high pH, facilitating the use of cost-effective and sustainable precious metal free catalysts. While high performance has been reached with platinum-group-metal (PGM) free cathodes in AEMFCs, the replacement of PGM-based anodes by PGM-free ones is a recognized challenge. Nickel-based catalysts are the most promising PGM-free hydrogen oxidation reaction (HOR) catalysts in alkaline medium, but nickel suffers from early surface oxidation at potentials above 0.1 V vs RHE, which in turn blocks the HOR on nickel. In order to mitigate the surface oxidation of nickel at HOR potentials, two main approaches are studied in the literature: optimization of nickel intrinsic properties by alloying with other earth abundant elements, or core@shell nanostructuration of nickel by a protective carbon shell.We will report on recent results obtained with this second approach, and the preparation of core@shell Ni@NC catalysts via the annealing of Ni-based MOFs. The latter were obtained either by autoclave or by a solvent-free mechanochemical synthesis. As reported in the literature [1], our observations confirm the significant effect of the pyrolysis atmosphere (NH3, H2, N2 and combinations) on the electrochemical activity of the catalysts. Other synthesis parameters will be shown to play a key role on the MOF structure and morphology as well as on the HOR activity of final materials. The materials were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques, including AEMFC tests. The presentation will discuss the results and correlate the material’s structure to their activity and stability.