Mixed spinel Ni0.5Zn0.5Fe2O4 on nickel foam for electrocatalytic oxygen evolution reaction: revealing the influence of temperature and promoting performance with zero voltage switching inductive heating

Abstract

The investigations of FeNi-based oxides’ oxygen evolution reaction (OER) behaviors in alkaline electrolyte at different temperatures can provide valuable guidance to develop water electrolysis technology. Herein, mixed spinel Ni0.5Zn0.5Fe2O4 nanosheets were synthetized on nickel foam (Ni0.5Zn0.5Fe2O4/NF) and studied as electrocatalysts for OER in 1.0 M KOH at 15~80℃. Compared to inverted spinel NiFe2O4 and normal spinel ZnFe2O4 nanosheets on nickel foam (NiFe2O4/NF and ZnFe2O4/NF), higher OER activity and faster kinetics were observed on Ni0.5Zn0.5Fe2O4/NF. At 1.23 V vs. RHE, the apparent activation energy of Ni0.5Zn0.5Fe2O4/NF, NiFe2O4/NF and ZnFe2O4/NF for OER was found to be 83.77, 91.59 and 110.56 kJ mol-1, respectively. At a OER current density of 100 mA cm-2 in 25 ℃ KOH electrolyte, the overpotential and Tafel slope of Ni0.5Zn0.5Fe2O4 were 323.7 mV and 62 mV dec-1, respectively, which were lower than that of NiFe2O4/NF (342.9 mV, 69 mV dec-1) and ZnFe2O4/NF (358.9 mV, 72 mV dec-1). Since OER is an endothermic and temperature dependent reaction, the OER activity and kinetics of Ni0.5Zn0.5Fe2O4/NF were found to be directly proportional to the temperature of KOH electrolyte. Accordingly, enhanced OER activity and kinetics were achieved on Ni0.5Zn0.5Fe2O4/NF under zero voltage switching (ZVS) inductive heating. Ni0.5Zn0.5Fe2O4/NF under ZVS inductive heating had high stability for OER, no obvious activity attenuation and morphology changes were observed when it worked at 50 mA cm-2 for 200 h of continuous reaction. Experimental investigations and finite element simulations revealed that the enhanced OER performance on Ni0.5Zn0.5Fe2O4/NF under ZVS inductive heating is attributed to the formation of thermal (contribution rate: 85.6%) and electric (contribution rate: 14.4%) fields to reduce reaction activation energy and accelerate OER simultaneously.