Electrochemical synthesis of CoOOH–Co(OH)2 composite electrode on graphite current collector for supercapacitor applications

Abstract

CoOOH–Co(OH)2 film composed of hexagonal nanoflakes and flaky nanosheets were obtained on graphite current collectors for charge storage electrodes. Cobalt film was firstly electrodeposited cathodically on the graphite electrode in pyrophosphate media. The film was then transferred into KOH and CoOOH–Co(OH)2 composite electrode was produced by the application of a potential. The composite electrode cycled in KOH had CoOOH domination in the oxidized form and Co(OH)2 dominated the composite at the reduced potential. FTIR, XRD and SEM characterizations of the electrodes proves the compositional, structural and morphological behavior of the electrodes depending on their oxidation states, respectively. The binder-free cobalt-based composite electrode illustrates a specific capacity of 886 F g−1 at 5 mV s−1. The electrochemical performance of the as-synthesized nano-composite electrode displays cycle stability of 90.1% retention after 1000 cycles. The rate limiting step was the mass transfer between the resulting electrode and KOH electrolyte which was a mixture of diffusional and surface controlled mechanisms.