Ni3S2/Co3S4 with controlled surface electron arrangement for high-performance aqueous energy storage

The smart design of electrode materials with distinctive structures has great influence on controlling the electronic band structure and enhancing the energy storage performance of supercapacitors and Ni–Zn batteries. In this study, from a Co-MOF nanosheet, a Ni3S2/Co3S4 nanosheet heterostructure with sulfur vacancies is prepared as an electrode material for Ni–Zn batteries and supercapacitors. As the existence of the heterostructure and sulfur vacancies can lower the OH− adsorption energy and band gap, providing ample active sites for ion diffusion, the Ni3S2/Co3S4-Sv displays enhanced electrical conductivity. The Ni3S2/Co3S4-Sv electrode delivers high specific capacitance (1855 F g−1 at 0.5 A g−1). It also displays high specific capacitance (167.3 F g−1 at 0.2 A g−1) and long cycling durability (72% capacitance retention after 20 000 cycles). By using Ni3S2/Co3S4-Sv as a positive electrode, the aqueous Ni–Zn battery delivers high specific capacity (220.6 mA h g−1 at 1 A g−1), superior rate capability and cycling durability (nearly no capacity decay after 2000 cycles at 5 A g−1). This work reveals the great potential of preparing a high performance cathode material in an aqueous energy storage system by using a heterostructure with sulfur vacancies.