Question

Under what conditions does nickel hydroxide, Ni (OH)₂, serve as a pseudocapacitive materials? Explain your reason.

Answer 1

Ni(OH)2electrode exhibit pseudocapacitive behaviour at a current density of 200 mA/g in 1 M KOH(aq).

Pseudocapacitive behaviour is exhibited by Ni(OH)2 because of redox reactions between Ni(OH)2 and NiOOH, both of them having two stable polymorphs: the α and β phases for Ni(OH)2, the γ and β phases for NiOOH11. The differences between these structures are the space between the layers and their organization, in which the α-Ni(OH)2 and γ-NiOOH have the larger distances and are less organized than the β-Ni(OH)2 and β-NiOOH, as can be seen in the scheme presented in Supplementary Fig. S1 (Electronic Supplementary Material). These structural differences lead to different reactivities, where the α-Ni(OH)2 and γ-NiOOH species present the better electrochemical responses. However, these phases are usually converted to the β phases during successive cycles of redox process and in highly alkaline media, decreasing their performances