Chemically synthesized cobalt oxide incorporated copper hexacyanoferrate (Co 3 O 4 –CuHCF) composite as an efficient supercapacitor electrode material

Copper hexacyanoferrate (CuHCF) is a promising material for energy storage systems due to its captivating features, such as its large surface area, three-dimensional absorbent network, reversible redox reactions and cost effectiveness. In order to further enhance its electrochemical properties, metal oxides, metallic ions, polymers and carbon-based materials can be incorporated. In this study, we focus on incorporating cobalt oxide (Co 3 O 4 ) into copper hexacyanoferrate to improve its electrochemical behaviour. Remarkably, the study reveals that the specific capacitance of the resulting Cobalt Oxide Incorporated Copper Hexacyanoferrate ( Co 3 O 4 –CuHCF) composite is as high as 1456 Fg −1 at a current density of 2 Ag −1 , which is significantly higher than that of pure CuHCF (264 Fg −1 at 2 Ag −1 ). The Ragone plot clearly demonstrates the excellent capacitive behaviour of the Co 3 O 4 –CuHCF composite, making it a highly promising electrode material for the fabrication of inexpensive and flexible supercapacitors. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis indicate that Co 3 O 4 sheets coated with CuHCF nanoparticles provide various electroactive surface sites that are responsible for the enhancement of electrochemical behaviour of prepared composite when employed as supercapacitor electrode material. The redox couples (Co 3+ /Co 2+ , Fe 3+ /Fe 2+ , Cu 2+ /Cu + ) as confirmed by X-ray Photoelectron Spectroscopy (XPS) also enhance the electrochemical properties. Additionally, the composite material retains specific capacitance upto 85% of its original value even after 2500 cycles, further demonstrating its exceptional durability and stability. These findings suggest that the Co 3 O 4 –CuHCF composite has significant potential for use in high-performance energy storage applications. Graphical abstract