Coupling of Multiple Reaction Mechanism in Dense Order-Disorder Nifeoxhy Toward High Effective and Durable Electrocatalytic Water Oxidation

Abstract

Nickel-iron systems have been considered as promising alternatives of noble-metal oxygen evolution reaction (OER) catalyst, however, their long-term high current density stabilities and further reducing the OER overpotential remain unsatisfactory. Herein, we propose a coupling mechanism of adsorbed evolution mechanism (AEM) and lattice oxygen mechanism (LOM) to improve the activity and stability of crystalline/amorphous Ni-Fe oxyhydroxides (c/a FeNiOxHy). The combination of X-ray adsorption near-edge structure, in-situ Raman and density functional theory investigates indicate that the amorphous component with cation vacancies can promote the formation of high state nickel to activate the lattice oxygen mechanism. The crystalline compounds following the AEM pathways can sustain structural stability and conductivity. Meanwhile, the formation of ferrous ion (Fe2+) can maintain Fe-O bond order during OER process to suppress Fe dissolution. As a result, the c/a FeNiOxHy catalyst exhibits superior electrocatalytic activity with ultralow overpotential 10 mA/cm2 at 188 mV and Tafel slope of 38.8 mV dec−1, also possesses excellent stability over 200 hours under large current density 100 mA/cm2, which is superior to the most reported catalytic. This work provides simple strategy and mechanistic understanding for the development of high-activity and durability OER electrocatalysts.

Keywords: oxygen evolution reaction, NiFeOxHy, lattice oxygen mechanism, electrocatalysis.