Boosting catalyst activity with high valency metal species through Fe doping on normal spinel NiCr2O4 for superior water oxidation

Abstract

Designing and tailoring valence states of transition metal has been highlighted as a potential technology to develop efficient electrocatalysts for water splitting because high valence metal sites enable to accelerate reaction kinetics for oxygen evolution reaction (OER). In this study, we designed and engineered spinel nickel-chromium oxide (NiFexCr2-xO4, 0 <= x <= 0.6) with high-valence metal sites and porous structure consisting of interconnected small nanoparticles using an in-situ Fe heteroatom doping synthesis route. The Fe-doped NiFexCr2-xO4 series (x = 0.2, 0.4, 0.6) catalysts exhibit superior OER activities compared to the pristine NiCr2O4 and benchmark IrO2 catalysts. Moreover, it is observed that for x = 0.2, the NiFexCr2-xO4 catalyst exhibited the best OER performance with a low overpotential of 187 mV at 10 mA cm(-2), a high current density of 172 mA cm(-2) at 0.28 V, and electrochemical long-term stability (decreasing only by similar to 3 %) after a 200 h test. We further demonstrate that the remarkably improved catalytic performance of NiFexCr2-xO4 is attributed to the increased high-valence metal species (Ni3+ and Cr6+) and the highly oxidative oxygen species (O-2(2-)/O-), which are highly active to accelerate catalytic reactions, as well as the improved charge transfer kinetics and the porous structural feature by rationally doped Fe. Thus, it is believed that this research provides a novel strategy for developing efficient, robust, and low-cost OER electrocatalysts.