Role of anions on structure and pseudocapacitive performance of metal double hydroxides decorated with nitrogen-doped graphene

Electrochemical capacitors (EC) bear faster charge-discharge; however, their real applications are still on a long away due to lower capacitance and energy densities which mainly arise from simple surface charge accumulation or/and reaction. Here, a novel synthesis strategy was designed to obtain the purposeful hybrids of nickel cobalt double hydroxide (NiCoDH) with genetic morphology to improve their electrochemical performance as electrode of EC. Nanostructures of metal hydroxides were grown on the nitrogen-doped graphene (NG) sheets by utilizing defects as nucleation sites and their composition was optimized both by tuning the ratio of Ni:Co as well as the counter halogen and carbonate anions to improve the porosity, stabilize the structure and mediate the redox reaction. The growth of the hybrids was guided by the Co ions through topochemical transformation supported by hoping charge transfer process and olation growth. NG overcoating successfully protects the nano-structure of NiCoDH during electrochemical test and enhances overall conductivity of the electrode, improving the mass and ionic transportations. As a result, the hybrid exhibits excellent capacitance of 2925 F g(-1) at 1 A g(-1), as well as long cyclic stability of 10,000 cycles with good capacity retention of 90% at 16 A g(-1). Furthermore, the hybrid shows excellent energy and power densities of 52 Wh kg(-1) and 3191 W kg(-1), respectively at discharge rate of 16 A g(-1). It is expected that this strategy can be readily extended to other metal hydroxides, oxides and sulphides to improve their electrochemical performances.