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 CoNi 2 S 4 /Ni 3 S 2 on nickel foam (CoNi 2 S 4 /Ni 3 S 2 @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 CoNi 2 S 4 /Ni 3 S 2 @NF electrode requires overpotential as low as 171 mV and 243 mV for HER and OER, respectively. Furthermore, the overall water splitting device with CoNi 2 S 4 /Ni 3 S 2 @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 CoNi 2 S 4 and Ni 3 S 2 synergistically optimized the electronic structure, thus enhancing the electrochemical water splitting performances. Surfaces oxidation of CoNi 2 S 4 /Ni 3 S 2 @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 CoNi 2 S 4 based materials. • CoNi 2 S 4 /Ni 3 S 2 catalyst was prepared via a facile hydrothermal method. • Electrocatalytic performances of CoNi 2 S 4 /Ni 3 S 2 @NF toward water splitting were investigated for the first time. • DFT calculations revealed the coupling interactions between CoNi 2 S 4 and Ni 3 S 2 can optimize the electronic structure. [ABSTRACT FROM AUTHOR]