Anions influence on the electrochemical performance of Co3X4 (X = O, Se) for supercapacitor: Experiments and theoretical calculations

In order to investigate the influence of the anions on the electrochemical performance of cobalt-based compounds, Co 3 O 4 and Co 3 Se 4 are studied and theoretically analyzed with the density functional theory (DFT). Avoiding of the traditional synthesis of the high-temperature annealing for the transition metal oxides, the cubic spinel phase Co 3 O 4 on a nickel foam (NF) substrate with a simple two-step hydrothermal method and Co 3 Se 4 with the core-branched structure by anions exchange method are prepared. The electrochemical measurements show that the capacitance and conductivity of Co 3 Se 4 are significantly better than those of Co 3 O 4 , and Co 3 Se 4 still maintain high capacity at high current density. Furthermore, the kinetics of electrode material Co 3 O 4 and Co 3 Se 4 are analyzed and compared. According to the calculation of the density of states, the results show the band gap of Co 3 O 4 is 2.18 eV and the Fermi energy line of Co 3 Se 4 enters into the conduction band, which means the conductivity of Co 3 Se 4 is better than that of Co 3 O 4 . Additionally, three redox reactions during the charge and discharge process of Co 3 O 4 are determined and the band gaps changes are also calculated.