One-pot methanol-mediated solvothermal synthesis of 3D porous Co-doped α-Ni(OH)2/RGO nanosheets as a high-performance pseudo-capacitance electrode

An environment-friendly and cost-effective route has been explored to prepare three-dimensional (3D) porous Co-doped α-Ni(OH)2 nanosheets vertically arranged on reduced graphene oxide (RGO) by one-pot methanol-mediated solvothermal synthesis. This process avoids the addition of any precipitating agent and oxidizing agent. Herein, methanol acts as solvent, structure-directing agent and it also can be oxidized to release OH−. In addition, Co doping is considered to be an effective approach to improve the electronic conductivity and electrochemical performance for energy conversion. Thus, experiments using different doping amounts of Co are performed. The different feed molar ratios of Co2+ to Ni2+ are simply controlled, and the ultrathin Co-doped α-Ni(OH)2/RGO nanosheets (Co2+:Ni2+ = 0.5:1) display the best capacitive property. The synthesized Co-doped α-Ni(OH)2/RGO nanosheet electrode exhibits the highest specific capacitance of 2322 F g−1 at current density of 1 A g−1, outstanding rate performance of 1933 F g−1 at 20 A g−1, and excellent lifetime cycle with 87.9% retention level after 1000 cycles at 10 A g−1. Moreover, an asymmetric supercapacitor is successfully manufactured with the Co-doped α-Ni(OH)2/RGO as a positive electrode and activated carbon as a negative electrode. The hybrid device delivers a maximum energy density of 38.9 Wh kg−1 and a maximum power density of 8000 W kg−1. Our supercapacitor exhibits a remarkable cycle stability along with 88.2% specific capacitance retained over 2000 cycles at 5 A g−1. These results may provide useful insights for fabricating high-performance electrode materials for energy storage applications.