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

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.