From Water and Ni Foam to a Ni(OH)₂@Ni Foam Binder‐Free Supercapacitor Electrode: A Green Corrosion Route

Abstract

Abstract In this work, a Ni(OH) 2 @Ni foam binder‐free electrode was obtained through the corrosion of Ni foam with ultrapure water under hydrothermal conditions. The structure, morphology, and surface chemical states of the obtained Ni(OH) 2 @Ni foam were characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy. The chemical formation mechanism is discussed. In addition, it was found that the loading amount and morphology of the deposited Ni(OH) 2 depend largely on the corrosion time. Furthermore, electrodes corroded for different times were then directly used as working electrodes to investigate the areal and specific capacitances of the deposited Ni(OH) 2 by using cyclic voltammetry, through which a relationship between the corrosion time, loading amount, morphology, and final capacitance is built up. The electrode with the highest areal capacitance was further studied with cyclic voltammetry, galvanostatic charge−discharge processes, as well as electrochemical impedance spectroscopy. The as‐prepared Ni(OH) 2 @Ni foam is a typical pseudocapacitance electrode. At a high current density of 5 mA cm −2 , the electrode exhibits an areal capacitance of 0.863 F cm −2 . For the deposited Ni(OH) 2 , its specific capacitance reaches 693 F g −1 at a current density of 4 A g −1 . After 3000 charge−discharge cycles at a current density as high as 10 A g −1 (12.5 mA cm −2 ), the areal capacitance retains 77.3 % of its initial value. The findings in this work could be meaningful for the corrosion preparation of related electrodes and the design of binder‐free electrodes.