Nanostructured cobalt hydroxide thin films as high performance pseudocapacitor electrodes by graphene oxide wrapping

Abstract

We synthesized binder-free Co(OH)₂ nanocrystals on nickel electrodes by the ammonia transfer method in an aqueous solution and kinetically-controlled their thickness and height to enhance the capacitance through the facile diffusion of electrolytes in the nanocrystals. As thinner Co(OH)₂ films were developed, the specific capacitance increased up to 1260 F g⁻¹ at a current density of 10 A g⁻¹. A thin layer of graphene oxide (GO) was used to wrap the Co(OH)₂ nanocrystals to create a pseudocapacitor with high specific capacitance and good cyclic stability. This synthetic strategy enabled us to maximize the electrochemical cell performance, reaching a specific capacitance of 2710 F g⁻¹ under 10 A g⁻¹. The GO coating provides an effective method to increase adhesion on the nickel electrodes and to reduce the decomposition of Co(OH)₂ during the charge–discharge process under high pH conditions. The prepared GO/Co(OH)₂ nanocomposite layers provided not only high electron mobility but also ionic conductivity, especially when operated at a high current density.