Customizing hetero-structured high-entropy alloy/oxide active site by regulating the exsolution strategy for highly efficient water splitting

Transition metals and their oxide materials are crucial in promoting hydrogen production efficiency via water splitting. However, the sluggish reaction kinetics of the oxygen evolution reaction (OER) process at the anode requires synergy between multiple active sites for effective activation and high electrocatalytic performance. In this study, an atomic contacted hetero-structured catalyst between high-entropy alloy (HEA) and high-entropy oxide (HEO) was synthesized for realizing highly active and robust OER. The heterogenous HEA/HEO catalyst was prepared by thermal reduction of the rock-salt HEO oxide of (NiCoFeCuAl)O, grown in situ on Ni foam via a fast self-propagating combustion method. The exsolution of face-centered cubic (FCC) structured NiCoFeCu HEA from the NiCoFeCuAlO matrix is beneficial for establishing a strong electron-transferring effect and providing more active reaction sites. Using combined actions of HEA/HEO heterointerfaces and nanoporous structure, the optimized catalyst (R-SNCFCA4.5) displays excellent OER performance with overpotential of 228 mV at current density of 10 mA cm ⁻², respectively, exhibiting a Tafel slope of 80.52 mV dec ⁻¹, and a 2.8 % decay activity for 100 h in alkaline medium. The R-SNCFCA6 catalyst with high extent exsolution of NiCoFeCu showcases the optimal HER performance. We reported the successful construction of HEA/HEO heterogeneous catalysts and demonstrated their application towards a highly efficient water splitting process.