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

Investigations into the behavior of FeNi-based oxides in the oxygen evolution reaction (OER) in an alkaline electrolyte at different temperatures can provide valuable guidance in developing a water electrolysis technology. Herein, mixed spinel Ni_0.5Zn_0.5Fe₂O₄ nanosheets were synthesized on nickel foam (Ni_0.5Zn_0.5Fe₂O₄/NF) and studied as electrocatalysts for the OER in 1.0 M KOH at 15–80 °C. Compared with 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 Ni_0.5Zn_0.5Fe₂O₄/NF. At 1.23 V vs. RHE, the apparent activation energy of Ni_0.5Zn_0.5Fe₂O₄/NF, NiFe₂O₄/NF and ZnFe₂O₄/NF for the OER was found to be 83.77, 91.59 and 110.56 kJ mol⁻¹, respectively. At an OER current density of 100 mA cm⁻² in 25 °C KOH electrolyte, the overpotential and Tafel slope of Ni_0.5Zn_0.5Fe₂O₄ were 323.7 mV and 62 mV dec⁻¹, respectively, which were lower than those of NiFe₂O₄/NF (342.9 mV, 69 mV dec⁻¹) and ZnFe₂O₄/NF (358.9 mV, 72 mV dec⁻¹). Since the OER is an endothermic and temperature-dependent reaction, the OER activity and kinetics of Ni_0.5Zn_0.5Fe₂O₄/NF were found to be directly proportional to the temperature of the KOH electrolyte. Accordingly, enhanced OER activity and kinetics were achieved on Ni_0.5Zn_0.5Fe₂O₄/NF under zero-voltage switching (ZVS) inductive heating. Ni_0.5Zn_0.5Fe₂O₄/NF under ZVS inductive heating had high stability for the OER, and no obvious activity attenuation or morphology changes were observed after continuous reaction for 200 h at 50 mA cm⁻². Experimental investigations and finite element simulations revealed that the enhanced OER performance on Ni_0.5Zn_0.5Fe₂O₄/NF under ZVS inductive heating is attributed to the formation of thermal (contribution rate: 85.6%) and electric (contribution rate: 14.4%) fields, which reduce the reaction activation energy and accelerate the OER simultaneously.