Synthesis and characterisation of Co–Co(OH)2 composite anode material on Cu current collector for energy storage devices

A Co–Co(OH)2 modified electrode on inexpensive Cu substrate was synthesized at room temperature and demonstrated to be a promising anode material for energy storage devices. A modified Co film was obtained potentiostatically and was then potentiodynamically treated with KOH solution to form Co(OH)2. Co–Co(OH)2 coatings were obtained and were dominated by Co(OH)2 at the oxidized side, whereas Co dominant Co–Co(OH)2 occurred at the reduced side (−1.1 V). As OH− ions were able to diffuse into (out of) the film during oxidation (reduction) and did not react with the Cu current collector, the Co–Co(OH)2 electrode can be used as an anode material in energy storage devices. Although the specific capacitance of the electrodes varied depending on thickness, the redox reaction between the modified electrode and KOH electrolyte remained the same consisting of a surface-controlled and diffusion-controlled mechanism which had a desirable fast charge and discharge property. Capacity values remained constant after 250 cycles as the film evolved. Overall capacity retention was 84% for the film after 450 scans. A specific capacitance of 549 F g−1 was obtained for the Co–Co(OH)2 composite electrode in 6 M KOH at a scan rate of 5 mV s−1 and 73% of capacitance was retained when the scan rate was increased to 100 mV s−1.