Se-induced underpotential deposition of amorphous CoSe₂ ultrathin nanosheet arrays as high-efficiency oxygen evolution electrocatalysts for zinc–air batteries

Zinc–air batteries are regarded as ideal candidates for next-generation energy conversion and storage devices, but their conversion efficiency is mainly limited by the sluggish kinetics of the oxygen evolution reaction (OER). Therefore, development of highly active and durable non-noble-metal OER catalysts is of great significance to promote their industrialization process. Herein, we electrodeposit amorphous CoSe₂ ultrathin nanosheet arrays which exhibit a low overpotential of ∼0.287 V at 10 mA/cm² and a Tafel slope of ∼62 mV/dec toward the OER in 1 M KOH. This catalytic activity is superior to their crystalline counterpart, commercial RuO₂, and most of the reported Co-based catalysts. It can be mainly attributed to the lowered adsorption free energy of OER intermediates and improved charge transfer ability with a phase transformation from the crystalline state to the amorphous state, besides the intrinsic catalytic activity of CoSe₂. When serving as an air cathode in a zinc–air battery, the amorphous CoSe₂ also realizes a larger power density and a better long-term cyclability compared with those of crystalline CoSe₂ and Pt/C–RuO₂ electrodes. This work offers a new underpotential deposition strategy to fabricate high-activity amorphous catalysts and demonstrates its great potential for practical applications.