Graphene quantum dots-decorated N-doped Bi2MoO6 hollow nanostructures: Coupling defect engineering with interface engineering toward enhanced charge storage for supercapacitors

The practical applications of transition-metal oxides as electrode materials for supercapacitors are still impeded by their intrinsically poor electrical conductivity and limited number of electroactive sites. Herein, a defect engineering strategy combined with interface engineering is adopted to create nitrogen-doped bismuth molybdate (N-BMO) hollow nanostructures decorated with graphene quantum dots (GQDs). Theoretical calculation and experimental results indicate that the N doping in BMO can enhance electrical conductivity of N-BMO by reducing its electronic band gap. Moreover, the surface decoration of GQDs on N-BMO enables higher electrical conductivity and more electroactive sites. More importantly, a built-in electric field is formed at the N-BMO/ GQD interface due to their Fermi-level difference, which favors fast interfacial charge transfer and accelerate electrode reaction kinetics. Accordingly, the optimized N-BMO@GQD electrodes yield higher specific capacities (572 and 435 C g(-1) at 1 and 10 A g(-1), respectively) and better cycling stability (91 % capacity retention after 10000 cycles at 5 A g(-1)) compared to pristine BMO electrode. Moreover, an assembled asymmetric supercapacitor device with N-BMO@GQD as positive electrode can deliver an energy density of 45.2 Wh kg(-1) at 801 W kg(-1). This study showcases an efficient strategy to design and develop promising BMO-based electrode materials for supercapacitors.