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

Abstract

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 mV s−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. Researchers from China have discovered a cost-effective way to produce supercapacitors on large scales using nickel foam. This three-dimensional porous metal is an ideal electrode for high-capacity energy storage because of its lightweight, corrosion-resistant structure. To achieve supercapacitance, however, researchers must insert active substances, such as graphene, deep into the nickel pores. Xihong Lu and colleagues from Sun Yat-Sen University solved this problem by immersing commercial-grade nickel foam into hot hydrochloric acid for several minutes. The one-step reaction pitted the formerly smooth nickel foam surface and created a thin outer ‘shell’ of nickel oxide that surrounded an inner nickel ‘core’. Electrochemical experiments revealed that the favorable core–shell structure, combined with a more accessible surface area achieved from the acid etching, yielded an energy-dense supercapacitor electrode that was effective for more than 100,000 charge–recharge cycles. A novel and cost-effective activation process has been developed to macroscopically produce three-dimensional (3D) porous Ni@NiO core-shell electrode by activated Ni foam (ANF) in HCl aqueous solution. The ANF electrode yielded a remarkable areal capacitance of 2.0 F cm−2 at a high current density of 8 mA cm−2 and exhibited ultrahigh long-term cycling stability without any decay of capacitance after 100 000 cycles.