All-redox hybrid supercapacitors based on carbon modified stacked zinc cobaltite nanosheets

Abstract

The role of energy in the present century has increased with the fast advancement of the global economy. In this regard, hybrid supercapacitors (HSCs) as energy storage systems have become an extensive research focus worldwide. This study reports the synthesis of carbon-loaded ZnCo₂O₄ stacked nanosheets via an in situ hydrothermal process followed by annealing. The electrochemical response was tested in a 2-electrode system. The optimized composite exhibited a capacitance of ∼527.6 F g⁻¹ at 5 mV s⁻¹. The symmetric SC (SSC) possessed an energy density (E_d) of ∼17.3 W h kg⁻¹ corresponding to a power density (P_d) of 2.25 kW kg⁻¹. Two asymmetric all-redox HSCs have also been fabricated using an optimized composite material as the positive electrode. The previously synthesized MnCo₂O₄/AC (HSC1) and MnO₂/AC (HSC2) were taken as negative electrodes. HSC1 exhibited an E_d of ∼24.4 W h kg⁻¹ corresponding to a P_d of ∼0.8 kW kg⁻¹. On the other hand, HSC2 exhibited the highest E_d of ∼30.8 W h kg⁻¹ at 2.4 kW kg⁻¹. The real-time application of the composite is tested with the fabricated HSCs. HSC1 exhibited a capacitive retention of ∼72.2% after 10 000 cycles. On the other hand, HSC2 exhibited a capacitive retention of ∼73.4% after 10 000 cycles. The SSC, HSC1, and HSC2 illuminated a 39 red LED panel for ∼3 min, 7 min, and 13 min, respectively. The results suggested the promising performance of all-redox HSCs. The overall results present a sustainable approach for creating hierarchical energy materials for the construction of future energy-storage systems.