Self-Formation of Compositionally Complex Surface Oxides on High Entropy Alloys: A Route to Sustainable Catalysts

Sustainable catalysts rely on abundant elements which are prone to oxidation. A new route to non-noble electro-catalysts is opened by directing the formation of unavoidable surface oxides towards creating a few atomic layers of an active and stable electrocatalyst, which is in direct contact with its metallic, conducting support. This is enabled by combining the possibilities of compositionally complex solid solutions with accelerated atomic-scale surface characterization. Surface composition changes from the as-synthesized state to states after exposure to the oxygen evolution reaction (OER) are investigated using a Cantor-alloy-catalyst-coated tip array for atom probe tomography. Whereas the as-deposited film has a 3 nm thick native oxide, initial and prolonged OER exposures result in an oxygen-influenced surface layer equilibrium, which shows a lower oxidation depth and altered metal composition. This demonstrates that as-synthesized complex compositions can be used to obtain active and stable surface oxides under electrochemical load.