Molybdenum-vanadium diboride core @ amorphous nanoporous carbon shell composite as a novel electrode material for hybrid supercapacitor

Transition metal borides (TMB) are among one of the brightest prospects for aqueous supercapacitor due to their extraordinary capacitive performances. However, majority of the reported TMBs to date are amorphous, which slows the electron transfer and can even disrupt the structure during cycling. Herein, we report, grain boundaries enriched molybdenum-vanadium diboride in a carbon matrix (Mo-V-B-2@C) possessing well-defined amorphous shell with crystalline core morphology, synthesized by novel and controlled approach. The crystalline Mo-V-B-2 in this structure facilitates ion diffusion and optimizes electronic conductivity, while nanoporous carbon maintains the structure's stability, resulting in a high specific capacitance (2368 F g(-1) at 4 A g(-1) in 1 M H2SO4), remarkable rate performance (1620 F g(-1) at 20 A g(-1)), and outstanding cycling stability (142 % retention after 10,000 GCD cycles). Grain boundaries generate strained regions acting as active sites in the nanostructure for boosted charge storage characteristics. The Mo-V-B-2@C parallel to Mo-V-B-2@C symmetric cell exhibits enhanced specific capacitance (512 F g(-1) @ 1 A g(-1)), excellent cycling stability (125 % after 10,000 GCD cycles) with high energy/power density (65.1 W h kg(-1) and 471.7 W kg(-1)). Such an effective novel approach throws new light on the synthesis and application of TMBs and similar charge storage materials with augmented grain boundaries for energy storage applications.