Hybrid cobalt-nickel oxalate/electrochemically exfoliated doped graphene composite for supercapacitor applications

In this work, a hydrothermal technique was adopted in obtaining a hybrid composite of cobalt-nickel oxalate (CoNi(C2O4)(2)center dot nH(2)O) and doped electrochemically exfoliated graphene (EEG) as supercapacitor electrodes. Extensive characterisation by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) technique, X-ray diffraction (XRD) and Raman spectroscopy revealed a sheet-like morphology of the doped-EEG integrated with CoNi(C2O4)(2)center dot nH(2)O nanoparticles. XPS analysis confirmed the presence of nitrogen, phosphorus, and sulphur in the EEG at low concentrations. The Raman vibration bands displayed the characteristic features of CoNi(C2O4)(2)center dot nH(2)O and EEG in the composite. The hybrid composite electrode evaluated in a half-cell configuration using a 3 M KOH aqueous electrolyte exhibited notable electrochemical performance with a maximum specific capacity of 139.2 mAh g(-1) (corresponding to 955.7 F g(-1) gravimetric capacitance) at a 1.0 A g(-1) current density. The electrodes were also continuously cycled for over 4500 constant charging-discharging steps and demonstrated about 86 % retention in capacity at 10.0 A g 1. The exhibited performance is linked to the high electrically conductive multi-atom doped EEG, and the CoNi(C2O4)(2)center dot nH(2)O/EEG composite's high specific surface area, which significantly contributes to the overall electrode's electrochemical stability when compared to the pristine CoNi(C2O4)(2)center dot nH(2)O electrode. This makes the CoNi(C2O4)(2)center dot nH(2)O/EEG composites suitable material electrodes for hybrid supercapacitor applications.