In situ fabrication of a Ni–Fe–S hollow hierarchical sphere: an efficient (pre)catalyst for OER and HER

Abstract

Designing low-cost, highly active and stable electrocatalysts is very important for various renewable energy storage and conversion devices. We fabricated a hierarchically porous Ni–Fe–S hollow hierarchical sphere through a solvothermal reaction of Ni²⁺, Fe³⁺ with a mixed solution of glycerol and isopropanol and a S²⁻ ion-exchange process. The incorporation of hybrid metal atoms significantly improved the oxygen evolution reaction (OER) activity of the hollow hierarchical sphere. Typically, the Ni–Fe–S hollow hierarchical sphere exhibits superior OER and HER activities to the single-phase Ni–S and Fe–S hollow hierarchical spheres, as well as most of the bifunctional electrocatalysts when catalyzing full water splitting. To drive a current density of 10 mA cm⁻², the Ni–Fe–S hollow hierarchical sphere requires an overpotential of only 223 and 115 mV for the OER and HER, respectively. Furthermore, the Ni–Fe–S hollow hierarchical sphere catalyst shows excellent durability after a long-term test. The superior activity and long-term stability demonstrate that the Ni–Fe–S hollow hierarchical sphere catalyst has promising potential for application in large-scale water splitting.