Development of an Amorphous Nickel Boride/Manganese Molybdate Heterostructure as an Efficient Electrode Material for...

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 (NiB) and crystalline square bar-like manganese molybdate (MnMoO₄) was prepared by a simple synthesis strategy. The formation of the NiB/MnMoO₄ 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 (NiB/MnMoO₄), the intact combination of NiB and MnMoO₄ leads to a large surface area with open porous channels and abundant crystalline/amorphous interfaces with a tunable electronic structure. This NiB/MnMoO₄ 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 NiB/MnMoO₄ 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 (NiB/MnMoO₄//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 NiB and MnMoO₄, which enhances the accessibility and adsorption of OH^- ions that improve electron transport. Moreover, the NiB/MnMoO₄//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 NiB and MnMoO₄ 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.