Ni@NiO Nanowires on Nickel Foam Prepared via “Acid Hungry” Strategy: High Supercapacitor Performance and Robust Electrocatalysts for Water Splitting Reaction

Ni/NiO core–shell nanowires on nickel foam (NF) are successfully synthesized using an “acid-hungry” strategy. The 3D electrode with large accessible active sites and improved conductivity, possesses an optimized ionic and electronic transport path during electrochemical processes. High areal capacitance of 1.65 F cm⁻² is obtained at an ultrahigh current density of 100 mA cm⁻², which is 19.88 times higher than pristine NF. The direct growth of nanowires makes the present supercapacitor electrode robust for long-term cycling test. By virtue of the favorable hydrogen adsorption energies on Ni⁰ and OH_ads energy on NiO or NiOOH, the 3D electrode exhibits high performance in hydrogen evolution reaction with 146 mV at η_{10mA cm^-2} and Tafel value of 72 mV dec⁻¹, and oxygen evolution reaction with 382 mV at η_{10mA cm^-2} and Tafel value of 103 mV dec⁻¹ in 1 m KOH. An electrolyzer using 3D electrodes as both anode and cathode can yield a current density of 10 mA cm⁻² at 1.71 V, and possesses superior long-term stability to an electrolyzer consisting of Pt/C||Ir/C. The present work develops an effective and low-cost method for the large-scale fabrication of Ni/NiO core–shell nanowires on commercial NF, providing a promising candidate for supercapacitors, fuel cells, and electrocatalysis.