Controlled synthesis of Ni(OH)2/Ni3S2 hybrid nanosheet arrays as highly active and stable electrocatalysts for water splitting

Abstract

The efficiency and stability of electrocatalysts are the key factors influencing the process of overall water splitting. In the research reported in this paper, the universal two-step method of co-precipitation and sulfuration is used to directly grow hierarchical nickel(II) hydroxide/trinickel disulfide [Ni(OH)₂/Ni₃S₂] hybrid on nickel foam. The results show that the Ni(OH)₂/Ni₃S₂-12h material used as the three-dimensional (3D) substrate electrode can maximize the synergy between the Ni(OH)₂ and Ni₃S₂, and it also exhibits high efficiency and persistent stability of the oxygen evolution reaction. The lower overpotential of only 270 mV at 20 mA cm⁻² compared to the benchmark of iridium(IV) oxide electrodes (300 mV of overpotential at 20 mA cm⁻²) benefited from the particular hybrid structure of Ni(OH)₂/Ni₃S₂-12h with large voids and volume and rapid charge transfer. In addition, the Ni(OH)₂/Ni₃S₂-12h material also shows a remarkable improved hydrogen evolution reaction activity compared to that of Ni(OH)₂, Ni(OH)₂/Ni₃S₂-9h and Ni(OH)₂/Ni₃S₂-15h individual catalysts, with which a low overpotential of only 211 mV is achieved at 20 mA cm⁻². Remarkably, Ni(OH)₂/Ni₃S₂-12h is used as a bifunctional water splitting catalyst, with which an overpotential of ∼340 mV is acquired at a very low cell voltage of 1.57 V with 10 mA cm⁻² in 1.0 M potassium hydroxide. These results demonstrate that most hydroxide/sulfide-based materials can be used as a electrocatalyst candidate and provide a superior synergy strategy, which provides a new way for robust water splitting electrochemical fabrication of high-performance and inexpensive electrode materials.