Magnetic electrode configuration with polypyrrole-wrapped Ni/NiFe2O4 core–shell nanospheres to boost electrocatalytic water splitting

Abstract

The exploration of transition metal-based electrodes with high efficiency, low-budget and excellent stability for overall water splitting has attracted increasing attention. To optimize the metal oxides as efficient bifunctional electrocatalysts, it is necessary to design not only their atomic and electronic structures but also the macroscopical electrode configuration. Herein, we report the preparation of conductive polypyrrole (PPy)-wrapped Ni/NiFe2O4 (Ni/NiFe2O4@PPy) nanospheres as a promising bifunctional electrocatalyst for the OER and HER. In the material design strategy, the PPy coating improves the conductivity and modulates the ion transmission rate between the electrolyte and Ni/NiFe2O4. The interaction between PPy and Ni/NiFe2O4 regulates the electronic structure and enhances the reaction efficiency of active sites. Furthermore, Ni/NiFe2O4@PPy nanospheres are employed to construct a binder-free magnetic electrode, which can well avoid the blockage of active sites and accelerate the gas release through the loosely assembled catalysts. The Ni/NiFe2O4@PPy with paramagnetic characteristics can be easily recovered for recycling by demagnetizing the electrodes. The specially designed magnetic electrodes show superior electrocatalytic activity with low overpotentials of 127 mV@10 mA cm−2 and 236 mV@100 mA cm−2 for HER and 265 mV@10 mA cm−2 and 370 mV@100 mA cm−2 for OER. The overall water electrolytic cell with Ni/NiFe2O4@PPy electrodes can achieve 10 mA cm−2 at 1.64 V with an excellent long-term stability. This work provides a novel material design and magnetic electrode construction strategy to improve the water splitting performance.