Single-wall and graphene-modified multiwall wasp nest shaped Bi2Mo2O9 self-assembly for performance-enhanced asymmetric supercapacitor

Abstract

The fascinating potential features of metal molybdates have attracted the attention of researchers due to their use as electrodes in energy storage devices of high performance. The present work demonstrates the implementation of the gel matrix technique in the preparation of single-phase single-wall S-Bi₂Mo₂O₉ and graphene-modified multi-walled M-Bi₂Mo₂O₉ wasp nest shaped self-assemblies. Graphene oxide nanosheets disturb the single-wall growth of Bi₂Mo₂O₉ that results in high-performance multiwall growth during the synthesis. The phase purity of the as-prepared S- and M-Bi₂Mo₂O₉ structures was verified with XRD analysis, and the absence of reduced graphene oxide formed in high-temperature annealing was verified for M-Bi₂Mo₂O₉. The morphology of the as-synthesized Bi₂Mo₂O₉ is a single or multi-walled wasp nest structure, indicating that the nanoparticles combined and formed a self-assembly. UV-visible spectroscopic studies of the bismuth molybdates helped to ascertain their optical properties. XPS analysis revealed the presence of O, Bi, and Mo in the Bi₂Mo₂O₉ particles. Electrochemical tests such as GCD, CV, and EIS were performed to examine the electrochemical behaviour of S- and M-Bi₂Mo₂O₉. The M-Bi₂Mo₂O₉ nanostructure exhibits a greater specific capacitance (Cs) of 831 F g⁻¹ at 1 A g⁻¹. Significant cycle stability of 87.97 percent retention after 5000 cycles was also reported when compared to S-Bi₂Mo₂O₉. The fabricated asymmetric device exhibited a maximum energy density of 54.16 W h kg⁻¹. Further, a power density of 750 W kg⁻¹ at 1 A g⁻¹ with a potential window of 0–1.5 V in 3 M KOH electrolyte was also observed and the chosen electrode retained 74.28% capacitance at 5 A g⁻¹ over 10 000 cycles. The notable electrochemical behaviour of the graphene-modified multi-walled wasp nest M-Bi₂Mo₂O₉ suggests that it could make an appropriate electrode material for energy storage systems.