Influence of the Molar Ratio of Co and V in Bimetallic Oxides on Their Pseudocapacitive Properties

Abstract

Bimetallic oxides have attracted significant attention as supercapacitor electrode materials due to their highly reversible redox processes, which are commonly associated with their surface chemistry and morphological features. In this work, bimetallic oxides with different molar compositions of Co and V, denoted Co0.6V0.4, Co0.65V0.35, and Co0.7V0.3, were synthesized by a modified solvothermal method using glycerol as stabilizing agent. The electrochemical characterizations were measured in a three-electrode cell. The role of the composition of CoV oxides on the pseudocapacitive properties was studied through the analysis of the energy storage mechanism following the power - law and Dunn's methodology (Wang et al., 2007), to obtain the b values. The synthesized CoV oxides were observed to be small conglomerate particles with undefined morphology and crystal structure corresponding to Co3V2O8 with small shifts due to crystal lattice distortion as was evidenced by TEM and XRD characterizations (Fig.1). These results indicated that the bimetallic oxides with a molar composition of Co0.6V0.4, Co0.65V0.35 and Co0.7V0.3 showed values of b of 0.91, 0.73, and 0.82 and a capacitive current contribution of 68, 63, and 66% analyzed at a scan rate of 1 mVs-1, respectively. In addition, the Co0.7V0.3 oxide showed a specific capacitance of 299 F g-1 at a current density of 0.5 A g-1 using 1 mol L-1 of KOH, and a high-rate capability of 81% at current densities of 0.5 - 6 A g-1. The better electrochemical performance of this sample is attributed to the synergistic effect of the Co and V atoms, since a minimal amount of V atoms may distort the crystal lattice and improve the electrolyte diffusion. Keywords: Co-V oxides; capacitance; pseudocapacitive; supercapacitors; rate capability. References Wang, J., Polleux, J., Lim, J. & Dunn, B. (2007). Pseudocapacitive contributions to electrochemical energy storage in TiO2 (anatase) nanoparticles. The Journal of Physical Chemistry C, 111(40), 14925–14931. Figure 1