Chemical synthesis of binder-free nanosheet-like cobalt vanadium oxide thin film electrodes for hybrid supercapacitor devices†

To enhance the performance of energy storage devices, electrode materials must be designed with a strategic alteration of morphology and electroactive sites, utilizing synergy in bimetallic oxides. Therefore, the present study comprehensively demonstrates that variations in cobalt and vanadate precursor concentrations during chemical bath deposition (CBD) of cobalt vanadium oxide (C-CV) electrode materials significantly impact their physicochemical (structural, morphological and surface area) and electrochemical properties. An increase in vanadium content in the C-CV electrodes induces a notable morphological transformation, from nanoflakes to nanosheets with altered size and surface area. With a nanosheet-like morphology and a surface area of 87.5 m² g⁻¹, the binder-free C-CV4 electrode synthesized with an optimal precursor composition of cobalt and vanadium (1 : 2) exhibits an outstanding specific capacitance (C_s) of 845.3 F g⁻¹ (a specific capacity of 422.6 C g⁻¹) at 1 A g⁻¹. Moreover, an aqueous hybrid supercapacitor device (AHSD) and a solid-state hybrid flexible supercapacitor device (SH-FSD) fabricated employing C-CV4 (cathode) and reduced graphene oxide (rGO) (anode) exhibit noteworthy C_s values of 115 F g⁻¹ and 105.2 F g⁻¹, respectively. Furthermore, the AHSD attains a specific energy (SE) of 40.9 W h kg⁻¹ at a specific power (SP) of 1.8 kW kg⁻¹, while the SH-FSD demonstrates an SE of 37.4 W h kg⁻¹ at a SP of 0.86 kW kg⁻¹. To prepare large-scale binder-free cobalt vanadium oxide with tunable morphology as the cathode material in hybrid energy storage devices, a feasible CBD method is adequate, as demonstrated by the electrochemical performance of hybrid supercapacitor devices.