Template ion-exchange synthesis of Co-Ni composite hydroxides nanosheets for supercapacitor with unprecedented rate capability

Because of the inherent poor conductivity, electrodes based on transition metal hydroxides (TMHs) for super capacitors (SCs) usually suffer from inferior rate capability. Herein, we present a strategy for the improvement of rate capability of Co-Ni hydroxides by creating well-structured composites via a template ion-exchange method (TIEM). The derived binary hydroxides own nanosheet morphology with ultrathin thickness of 5-10 nm, and display well-composited structure, large specific surface area as well as homogenous element distribution. Importantly, the inherent conductivity of the composite is twice more than that of the individual hydroxides. Featuring with these unique advantages, the hydroxide composite with optimized Co/Ni ratio viz. Co0.52N-i(0.48)(OH)(2), as electrode material for supercapacitor achieves performances superior to those of single hydroxides, including large capacitance (1608F/g@1.0 A/g), high energy density (55.9 Wh/kg@750 W/kg), long cycling stability, and greatly enhanced rate capability. Notably, the optimized composite exhibits an unprecedented rate capability of 90.6% from 1.0 to 20 A/g, much superior to that of Ni(OH)(2) (16%) and Co(OH)(2) (75.3%) and the reported Co-Ni composite hydroxides, posing as a promising candidate for energy storage devices. Overall, the present template ion-exchange strategy provides a simple method for the fabrication of well-structured composite metal hydroxides and opens an avenue for the use of such materials in fields such as energy storage, catalysis, sensor, and so on.