A three-dimensional multilevel nanoporous NiCoO2/Ni hybrid for highly reversible electrochemical energy storage

Abstract

Supercapacitors have received ever-increasing attention in the energy storage field owing to their fast charge–discharge rates and very high longevity. The battery-type transition metal oxides provide great choices for supercapacitor technologies as promising cathode candidates because they offer the advantages of high performance and low cost. Three-dimensional (3D) porous nanomaterials with large specific surface areas represent one class of alternative electrodes by virtue of their abundant active sites and continuous conductive matrix for redox reactions. Herein, a 3D multilevel nanoporous NiCoO₂ cathode with a conductive Ni matrix is fabricated by means of a one-step facile dealloying strategy. The dissolution of Al atoms from an alloy of NiCoAl in alkaline solution straightforwardly generates interconnected multilevel pore channels and ligaments as the building blocks, with large pores of around 150 nm and small pores mainly in the range of 2–10 nm. During the dealloying process, Co and a proportion of the Ni atoms undergo spontaneous oxidation and evolve to form a multilevel porous NiCoO₂/Ni hybrid without the involvement of any extra agents. Taking advantage of the 3D integrated backbone as well as the introduced Ni matrix, the as-prepared NiCoO₂/Ni cathode demonstrates high specific capacity (536.8 C g⁻¹/601.4 C cm⁻³ at a current density of 1 A g⁻¹) calculated by the total NiCoO₂/Ni loading. An asymmetric supercapacitor constructed by using NiCoO₂/Ni and active carbon as the electrodes displays a high energy density (38.4 W h kg⁻¹/24.2 W h L⁻¹) at a power density of 800 W kg⁻¹/503.6 W L⁻¹, and powerful output with 90.5% capacitance retention after cycling for as long as 20 000 loops. The exceptional energy storage performances make porous NiCoO₂/Ni a prospective cathode candidate in the field of supercapacitors.