Development of an Amorphous Nickel Boride/Manganese Molybdate Heterostructure as an Efficient Electrode Material for a High-Performance Asymmetric Supercapacitor.

The exploration of heterostructure materials with unique electronic properties is considered a desirable platform for fabricating electrode/surface interface relationships for constructing asymmetric supercapacitors (ASCs) with high energy density. In this work, a heterostructure based on amorphous nickel boride (Ni X B) and crystalline square bar-like manganese molybdate (MnMoO 4 ) was prepared by a simple synthesis strategy. The formation of the Ni X B/MnMoO 4 hybrid was confirmed by powder X-ray diffraction (p-XRD), field emission scanning electron microscopy (FE-SEM), field-emission transmission electron microscopy (FE-TEM), Brunauer-Emmett-Teller (BET), Raman, and X-ray photoelectron spectroscopy (XPS). In this hybrid system (Ni X B/MnMoO 4 ), the intact combination of Ni X B and MnMoO 4 leads to a large surface area with open porous channels and abundant crystalline/amorphous interfaces with a tunable electronic structure. This Ni X B/MnMoO 4 hybrid shows high specific capacitance (587.4 F g -1 ) at 1 A g -1 , and it even retains a capacitance of 442.2 F g -1 at 10 A g -1 , indicating superior electrochemical performance. The fabricated Ni X B/MnMoO 4 hybrid electrode also exhibited an excellent capacity retention of 124.4% (10000 cycles) and a Coulombic efficiency of 99.8% at a current density of 10 A g -1 . In addition, the ASC device (Ni X B/MnMoO 4 //activated carbon) achieved a specific capacitance of 104 F g -1 at 1 A g -1 and delivered a high energy density of 32.5 Wh.kg -1 with a power density of 750 W·kg -1 . This exceptional electrochemical behavior is due to the ordered porous architecture and the strong synergistic effect of Ni X B and MnMoO 4 , which enhances the accessibility and adsorption of OH - ions that improve electron transport. Moreover, the Ni X B/MnMoO 4 //AC device exhibits excellent cyclic stability with a retention of 83.4% of the original capacitance after 10000 cycles, which is due to the heterojunction layer between Ni X B and MnMoO 4 that can improve the surface wettability without causing structural changes. Our results show that the metal boride/molybdate-based heterostructure is a new category of high-performance and promising material for the growth of advanced energy storage devices.