Structural Engineering of Core–Shell Ni₃B@Ni(BO₂)₂ on V₂MoO₈ (0D@2D/1D) Composites: Advanced Strategies for Enhancing High Energy Density in Asymmetric Supercapacitors

The development of hierarchical core-shell structures and multicomponent metal boride/metal oxide-based composites presents a promising strategy to enhance supercapacitor (SC) performance. In this study, we synthesized a Ni₃B@Ni(BO₂)₂ (0D@2D) core-shell structure and integrated it with V₂MoO₈ (VMO) rods (1D) to form a Ni₃B@Ni(BO₂)₂/VMO (NB@NBO/VMO (0D@2D/1D)) composite. This composite was then used as an electrode material on a flexible carbon cloth (CC) substrate for SC applications. The 1D-VMO rods were derived from V-doped MoSe₂ nanosheets via hydrothermal synthesis and calcination, while the NB@NBO/VMO composite was obtained by using a liquid-phase method. Structural, compositional, and morphological characterizations were conducted using XRD, XPS, FE-SEM, and TEM-EDS. In a three-electrode system, the NB@NBO/VMO-50 composite showed an impressive <i>C</i>_s of 698 F g^-1 at 1 A g^-1, ascribed to its unique core-shell architecture, which enhances contact and faradaic properties, shortens ion diffusion paths, and provides abundant active sites. Notably, the NB@NBO/VMO-50 displayed excellent cyclic stability, retaining 75.1% of its capacitance after 10,000 cycles at 10 A g^-1. This performance is better than those of other electrodes, including pristine VMO/CC, NB/CC, NB@NBO/VMO-25, and NB@NBO/VMO-75. When evaluated in a two-electrode asymmetric SC system, the NB@NBO/VMO-50/CC||rGO device operated at 1.6 V and delivered a high energy density (ED) of 40.5 Wh kg^-1 at a power density (PD) of 800 W kg^-1. It also reached a PD of 16,000 W kg^-1 while maintaining an ED of 23.5 Wh kg^-1. The device also showed remarkable long-term durability, maintaining 79.3% of its capacitance and 99.9% Coulombic efficiency after 8000 charge-discharge cycles at 8 A g^-1, demonstrating its strong potential for next-generation energy storage applications.