Development of pseudocapacitive materials based on cobalt and iron oxide compounds for an asymmetric energy storage device

Abstract

Composite electrodes based on cobalt hydroxide and iron oxide, respectively, with silica as an under-layer were developed with the use of sol-gel and electrochemical deposition techniques. The electrodes demonstrate similar surface morphologies of the upper pseudocapacitive layer formed by lamellas. The composite Co-based electrodes as well as Fe-based electrodes with silica reveal higher values of capacitance retention after multiple charge-discharge process than the ones without it. The influence of OH−concentration upon pseudocapacitive behavior was estimated for Co–based electrodes. The mixed electrolyte with an extremely low alkali concentration proved to increase capacitance retention of the electrodes. A model of an asymmetric pseudocapacitor was fabricated with the use of the Co and Fe–based electrodes, pre-coated with silica. The use of differential capacitance technique in a full electrochemical cell allowed balancing charges of positive and negative electrodes within their potential windows. The maximum voltage range of 1.4 V was achieved for the cell which exceeds the window of electrochemical stability of water.