Enhanced electrochemical performance of CuCo₂O₄ nanowire arrays based solid-state symmetric supercapacitor by K₃[Fe(CN)₆] redox additive electrolyte

The redox additive in an aqueous gel electrolyte is reported as one of the efficient methods to improve the electrochemical supercapacitor performance. Here, we report the role of redox additive, potassium ferricyanide((K₃[Fe(CN)₆]), referred to as KFCN) for improving the electrochemical performance of binder-free, CuCo₂O₄ (CCO) nanowire arrays (NWs) based solid state symmetric supercapacitors (SSCs). The crystal structure and morphology of prepared CCO films are confirmed by X-ray diffraction (XRD) and field emission-transmission electron microscopy (FE-TEM). The elemental composition of CCO films is estimated as Cu_0.5Co_2.77O_3.82 via energy-dispersive X-ray spectroscopy (EDS) analysis. Surprisingly, the areal capacitance (or energy density at 5 mAcm⁻²) is significantly improved from 0.58 F cm⁻² (or 0.016 mWh cm⁻²) to 10.5 F cm⁻² (or 0.296 mWh cm⁻²), respectively, after the addition of KFCN to aqueous KOH electrolyte, as compared to bare KOH. Furthermore, CCO exhibits decent cyclic stability with 90 % capacitance retention up to 5000 CV cycles at the scan rate of 100 mV s⁻¹. Moreover, 2-terminal CCO NWs-based SSCs, employed with PVA-KOH-KFCN gel electrolyte, demonstrate a wider potential window of −0.9 to 0.9 V (1.8 V) with a 7-fold increase of energy density from 9.1 to 65 Wh kg⁻¹, as compared with that of PVA-KOH gel electrolyte. As practical validation, the operation of Red-LED for 3 min is demonstrated with PVA-KOH-KFCN gel-based SSC, manifesting that adding redox substance in aqueous electrolytes is one of the promising strategies for portable and wearable energy storage systems.