Effect of Mass Transport on the Charge Storage Mechanism of Cobalt Hydroxide Nanosheets in an Aqueous Electrolyte

Abstract

Although cobalt hydroxide (Co(OH)2) has received great attention as a layered electrode material for aqueous-based energy storage applications due to its high theoretical capacity, it is unstable and easily oxidized to be more stable phase in an aqueous medium. This leads to decrease in capacity and cycling performance, limiting its practical application. In addition, a wide range of electrolyte concentration (1-6M) has been utilized for Co(OH)2 electrode and the mechanisms related to charge storage performance were still unclear. To enhance the overall performance, a deep understanding of charge storage mechanisms of Co(OH)2 corresponding to mass transport and electrolyte concentration is needed. Herein, the hydrodynamic voltammetry experiment using rotating disk electrode (RDE) was performed to study the effect of mass transport of the ions in electrolytes on the charge storage mechanism of the as-electrodeposited cobalt hydroxide nanosheets in various concentrations of an aqueous potassium hydroxide (KOH) solution. The cycling performance related to rotation rates and electrolyte concentrations was also studied. Additionally, Operando X-ray absorption spectroscopy (XAS) was carried out to investigate the change in oxidation state of Co(OH)2 in different concentrations of KOH during charge/discharge processes. The set of information in this work will pay the way for further development of the cobalt-based energy storage technologies.