Boosting cation desorption, anion adsorption and surface redox reaction kinetics of Co3O4 by oxygen vacancy

Abstract

Although defect engineering is widely reported in catalysis, the influence of defects on electrochemical performance is less reported and the defect-related electrochemical mechanism is not fully understood. In this work, the oxygen vacancy concentration is controlled simply by calcining different precursors. The Co3O4 samples by prepared cobalt-thiourea coordination and cobalt nitrate precursors are named as S1 and S2, respectively. It is found that cobalt-thiourea coordination compound can provide an oxygen-rich skeleton, thus reducing oxygen vacancy; the specific capacitance of S1 (79.5 F/g) is 12.5 times higher than that of S2 (5.9 F/g) at 0.2 A/g. The remarkably improved capacitance is mainly attributed to the appropriate amount of oxygen vacancy for S1. Theory calculations confirm that an appropriate concentration of oxygen vacancy favors the desorption of K+ and the adsorption of OH–, and the kinetics of surface redox reaction; while excessive oxygen vacancies are disadvantageous to the electrochemical process. Additionally, the S1-based asymmetric supercapacitor (ASC) displays a high energy density of 176 μWh/cm3, a high power density of 218 mW/cm3, and a long cycling life (72.6% capacitance retention after 2500 charge/discharge cycles). The ASC is so flexible that it can be easily assembled in series to drive a light-emitting diode to work. This work provides a simple, low-cost method for producing high-quality electrode materials on a large scale.