Tentacle-like core–shell CoNi2S4/C3N4 bifunctional electrocatalysts for efficient overall alkaline water splitting

Abstract

Stable and efficient bifunctional electrocatalysts are of great significance for sustainable energy conversion and human society sustainability. However, conventional electrocatalytic materials tend to exhibit high overpotentials and unsatisfactory chemical activities. Herein, we construct novel CoNi₂S₄/C₃N₄ nanowires on a nickel foam (NF) electrode as a bifunctional electrocatalyst for alkaline water splitting by a two-step hydrothermal and thermal annealing process. The prepared CoNi₂S₄/C₃N₄ electrocatalyst exhibits superior HER (e.g. 40 mV (η_H2¹⁰)) and OER (e.g. 110 mV (η_O2¹⁰)) activities in a 1 M KOH electrolyte, which are much smaller than those of bare NF, Co@NF, NiCoO@NF and most reported materials. Furthermore, the stability test at 10 mA cm⁻² for 20 h for the CoNi₂S₄/C₃N₄ electrocatalyst shows no obvious decay and proves the excellent stability of CoNi₂S₄/C₃N₄. In this work, the unique tentacle-like CoNi₂S₄/C₃N₄ nanowire nanostructure leads to minimized interfacial resistance and abundant channels during electrocatalysis. Moreover, comprehensive analysis results show that Ni(Co)OOH active sites, which are beneficial for excellent OER activity, partially form on the surface of CoNi₂S₄/C₃N₄ during electrocatalysis. Finally, the CoNi₂S₄/C₃N₄∥CoNi₂S₄/C₃N₄ two-electrode system is constructed and it exhibits a low-voltage water splitting capability of 1.40 V.