Hierarchical in(OH)₃/rGO battery-type electroactive material on nickel foam for high-performance supercapacitors

Hydroxide-based electroactive materials are promising for supercapacitors due to their high energy storage capacity. Four sets of In(OH)₃, In(OH)₃−Cysteine, In(OH)₃/rGO, and In(OH)₃/rGO−Cysteine electrodes were synthesized on nickel foam via a hydrothermal route. The electrode morphology strongly depended on GO and cysteine incorporation. Cyclic voltammetry and charge-discharge studies revealed a reversible Faradaic redox mechanism characteristic of battery-type behavior. In(OH)₃/rGO−Cysteine electrode exhibited the highest specific capacity (251.34 mA h g⁻¹ at 4 mA cm⁻²), which is substantially higher than the specific capacity of the In(OH)₃ (21.51 mA h g⁻¹), In(OH)₃/rGO (41.78 mA h g⁻¹), and In(OH)₃−Cysteine (235.21 mA h g⁻¹). It also showed superior stability, retaining 117.67 % capacity after 1000 cycles. Electrochemical impedance spectroscopy confirmed lower charge-transfer resistance and enhanced electrolyte diffusion. A symmetric supercapacitor with In(OH)₃/rGO−Cysteine electrodes in 1 M KOH delivered a specific capacity of 9.88 mA h g⁻¹ at 0.5 mA cm⁻², maintaining 89.25 % capacitance and 93.89 % coulombic efficiency after 3000 cycles. The hierarchical structure and synergistic effects of rGO and cysteine contribute to exceptional electrochemical performance, making this composite a strong candidate for high-performance supercapacitors.