Exploring the intrinsic active sites and multi oxygen evolution reaction step via unique hollow structures of nitrogen and sulfur co-doped amorphous cobalt and nickel oxides

The unique designed and their tunable intrinsic active sites for OER have a key role in alternating the noble metal (IrO₂). Herein, we fabricated Co-Ni-N-S-O nanocage through a simple self-catalytic process. The outstanding OER performance is based on the rich defect sites and oxygen vacancies in the amorphous phase with abundant surface area attributed to the hollow nanocage structure, and the ‘ensemble effect’ caused by N and S doping. The high intrinsic active surface area of Co-Ni-N-S-O was confirmed by double-layer capacitance (C_dl: 5.39 mF/cm²), and the ‘ensemble effect’ was determined through XPS and XAS analysis. The metal centers were located to a higher oxidation state, resulting the advantageous for the formation of OER intermediates (*OOH), as proved by operando XAS analysis. The Co-Ni-N-S-O catalyst provides a valuable strategy to design electrocatalysts of high efficiency and expand the applications of catalysts based on amorphous metal oxides.