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

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 (ηH210)) and OER (e.g. 110 mV (ηO210)) 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.