Flower-like CoNi2S4/Ni3S2 nanosheet clusters on nickel foam as bifunctional electrocatalyst for overall water splitting

Efficient electrocatalysts based on earth-abundant elements are urgently required for promoting the efficiency of electrochemical water splitting. In this work, heterostructures of CoNi2S4/Ni3S2 on nickel foam (CoNi2S4/Ni3S2@NF) are synthesized by a facile one-step hydrothermal method as promising bifunctional electrocatalysts. To achieve an electrocatalytic current density of 10 mA cm−2 in 1 M KOH solution, the CoNi2S4/Ni3S2@NF electrode requires overpotential as low as 171 mV and 243 mV for HER and OER, respectively. Furthermore, the overall water splitting device with CoNi2S4/Ni3S2@NF electrode as both cathode and anode requires 1.65 V to offer current density of 10 mA cm−2. Density functional theory calculations reveal that the strong coupling interactions between CoNi2S4 and Ni3S2 synergistically optimized the electronic structure, thus enhancing the electrochemical water splitting performances. Surfaces oxidation of CoNi2S4/Ni3S2@NF electrode is considered to hinder the electrochemical activities for OER. The present work not only provides a promising bifunctional electrocatalyst for water splitting but also expands the applications of CoNi2S4 based materials.