Scalable self-growth of Ni@NiO core-shell electrode with ultrahigh capacitance and super-long cyclic stability for supercapacitors

Three-dimensional (3D) electrodes have been demonstrated to be promising candidates for high-performance supercapacitors because of their unique architectures and outstanding electrochemical properties. However, the fabrication process for current 3D electrodes is not scalable. Herein, a novel and cost-effective activation process has been developed to macroscopically produce 3D porous Ni@NiO core-shell electrodes with enhanced electrochemical properties. The porous Ni@NiO core-shell electrode obtained by activated commercial Ni foam (NF) in a 3 M HCl solution yields an ultrahigh areal capacitance of 2.0 F cm(-2) at a high current density of 8 mA cm(-2), which is substantially higher than that of most reported 3D NF-based electrodes. Moreover, the activated NF (ANF) electrode exhibited super-long cycling stability. Owing to the increased accessible surface area and continual formation of electrochemically active NiO during cycling, the areal capacitance of the ANF electrode did not exhibit any decay and instead increased from 0.47 to 1.27 F cm(-2) after 100 000 cycles at 100 mVs(-1). This is the best cycling stability achieved by a 3D NF-based electrode. Additionally, a high-performance asymmetrical supercapacitor (ASC) device based on the as-prepared ANF cathode and a reduced graphene oxide (RGO) anode was also prepared. The ANF//RGO-ASC device was able to deliver a maximum energy density of 1.06 mWh cm(-3) and a maximum power density of 0.42 W cm(-3).