Surface resistance change during nickel hydroxide phase transformations

Abstract

Nickel hydroxide undergoes profound structural transformations under prolonged potential cycling in alkaline solutions. In this work, gold film electrodes modified with different nickel hydroxide coverages were subjected to continuous potentiodynamic cycling in alkaline medium, while the simultaneous evolution of voltammetric and surface resistance records was monitored until stable responses were obtained. A surface resistance (SR) increase proportional to the nickel hydroxide coverage was observed at potential values more negative than − 0.3 V (vs. SCE), which was attributed to the deposition of nickel adatoms from the reduction of nickel hydroxide layers. This SR change was analysed on the basis of the electron scattering theory, considering that nickel adatoms act as scatterers for the reflection of gold conduction electrons. The nickel adatom layer produced from the reduction of the nickel hydroxide structure formed during the first voltammetric scan potential cycles (< 40) exhibits a more specular reflection than that generated after a larger number of potential cycles (> 140). As the specularity of a layer for electron scattering can be associated with scatterer compactness, the distance between nickel atoms in the former nickel adatom structure is shorter than that in the last one.