High mass loading Ni₄Co₁-OH@CuO core-shell nanowire arrays obtained by electrochemical reconstruction for alkaline energy storage

The design of three-dimensional (3D) core-shell heterostructures is an efficient method to achieve high mass specific capacity of electroactive materials under high mass loading. In this work, porous Ni₄Co₁-OH nanosheets with a mass loading of 7.7 mg·cm^-2 are obtained by using Ni₄Co₁-(NO₃)₂(OH)₄ supported on the CuO nanowires as precursors via an unavoidable electrochemically induced phase reconstruction. During the electrochemical reconstruction process, the NO₃^- anions in Ni₄Co₁-(NO₃)₂(OH)₄ are easily replaced by OH^- anions in the electrolyte. The phase reconstruction is accompanied by the decrease of ionic diffusion resistance and the increase of pore volume, and the shift of binding energy. The obtained Ni₄Co₁-OH nanosheets show a high mass specific capacity of 363.6 mAh·g^-1 at 5 mA·cm^-2. The as-fabricated alkaline hybrid supercapacitor and Ni-Zn battery deliver high energy density of 293.1 and 604.9 Wh·kg^-1, respectively, indicating excellent alkaline energy storage performance.