Nanostructured CuCo ₂ O ₄ Binder-Free Electrodes Supported on Stainless Steel for Supercapacitors and Water Splitting

The progress of advanced nanostructured electrode materials capable of simultaneously supporting energy storage and energy conversion is important for next-generation electrochemical (EC) systems. In this study, binder-free CuCo 2 O 4 nanostructures were grown on stainless steel substrates via a hydrothermal approach. They are labeled C1, C2, C3, and C4, corresponding to reaction times of 2, 3, 4, and 5h, respectively, at a fixed temperature. Their supercapacitor (SC) and electrochemical water splitting performances were systematically evaluated. X-ray diffraction and microscopic analyses confirmed the formation of polycrystalline CuCo 2 O 4 with heterogeneous nanostructures. Among the synthesized samples, the C3 electrode, synthesized at 120 °C for 4 h, exhibits the best EC performance. It delivered a specific capacitance of 376 F g –1 and a specific capacity of 73.09 mAh g –1 at a scan rate of 5 mV s –1 in 1 M KOH, along with excellent cycling stability, retaining 83% of its initial capacitance after 5000 cycles. A hybrid SC device assembled using C3 as the positive electrode and activated carbon as the negative electrode attained a maximum energy density of 24.57 Wh kg –1 at a power density of 1120 W kg –1, demonstrating its practical applicability. In addition to energy storage, the C3 electrode also shows efficient electrocatalytic activity toward water oxidation, requiring a low overpotential of 301 mV to reach 10 mA cm –2 and a favorable Tafel slope of 73 mV dec –1, along with excellent stability. Overall, these findings demonstrate that binder-free CuCo 2 O 4 nanostructures developed on stainless steel are promising bifunctional materials for integrated energy storage and conversion applications.