Novel design of nickel cobalt boride nanosheets-decorated molybdenum disulfide hollow spheres as efficient battery-type materials of hybrid supercapacitors.

Transition metal borides (TMBs) with high theoretical capacitances and excellent electronic properties have attracted much attention as a promising active material of supercapacitors (SCs). However, TMB nanoparticles are prone to conduct self-aggregation, which significantly deteriorates the electrochemical performance and structural stability. To address the severe self-aggregation in TMBs and improve the active material utilization, it is imperative to provide a conductive substrate that promotes the dispersion of TMB during growths. In this work, sheet-like nickel cobalt boride (NCB) was grown on molybdenum disulfide (MoS) hollow spheres (H-MoS) by using simple template growth and chemical reduction methods. The resultant NCB/H-MoS-50 was observed with uniform NCB nanosheets structure on the surface of the H-MoS and stronger MB bonding. After optimizing the loading amount of H-MoS, the optimal composite (NCB/H-MoS-50) modified nickel foam (NF) exhibits a superior specific capacity (1302 C/g) than that of the NCB electrode (957 C/g) at 1 A/g. Excellent rate capability of 84.8% (1104 C/g at 40 A/g) is also achieved by the NCB/H-MoS-50 electrode. The extraordinary electrochemical performance of NCB/H-MoS-50 is credited to the unique nanosheet-covered hollow spheres structure for facilitating ion diffusion and versatile charge storage mechanisms from the pseudocapacitive behavior of H-MoS and the Faradaic redox behavior of NCB. Furthermore, a hybrid SC is assembled with NCB/H-MoS-50 and activated carbon (AC) electrodes (NCB/H-MoS-50//AC), which operates in a potential window up to 1.7 V and delivers a high energy density of 76.8 W h kg at a power density of 850 W kg. A distinguished cycling stability of 93.2% over 20,000 cycles is also obtained for NCB/H-MoS-50//AC. These findings disclose the significant potential of NCB/H-MoS-50 as a highly performed battery-type material of SCs.