Ternary cobalt-iron sulfide as a robust electrocatalyst for water oxidation: A dual effect from surface evolution and metal doping

Water electrolysis is considered as a promising sustainable technology to produce hydrogen thereby reducing dependence on fossil fuels. The oxygen evolution reaction (OER), a half reaction of water electrolysis is hampered by its slow kinetics. Developing high performance electrocatalysts for enhancing OER kinetics is the main bottleneck of this technology. In this study, we synthesize a ternary cobalt iron disulfide as a pre-catalyst for OER. After the activation step, the synthesized catalyst transformed to cobalt-iron amorphous oxide with oxygen defects as an efficient catalyst for OER. At its optimized Co/Fe ratio, equal to 3:1, the activated catalyst requires only 267 mV overpotential to reach the current density of 10 mA cm(-2), while Tafel slope is 34 mV dec(-1). Density functional theory calculation reveals that the active phase of the OER process is a thin layer of oxide that forms during the voltammetry activating process and the reduced energy barrier of rate determining step contributes to the excellent OER performance of cobalt-iron amorphous oxide.