Observation of Nickel Hydroxide Layer on Ni Electrode by in situ Atomic Force Microscopy

The layer of nickel hydroxide was formed on the surface of polycrystalline Ni immersed in 1 M KOH by cycling the potential in the range between -0.1 and 0.6 V vs. Pt in 1 M KOH. The layer thickness of 8.5 nm, estimated by an electrochemical method, corresponded to about 10 monolayers of Ni(OH)$\text{}_{2}$. The changes of thickness of the nickel hydroxide film during the process of its oxidation and reduction were monitored by the use of in situ atomic force microscopy with the tip fixed and the electrode potential scanned between -0.1 and +0.6 V at a scan rate of 100 mV/s. The process of oxidation resulted in the film thickness decrease by about 3 nm. This change could be explained as to be due to the removal of a proton from Ni(OH)$\text{}_{2}$ layer.