Dependency of anodic and cathodic peak currents on square root of scan rates in
CVs of electrodeposited nickel electrodes in aqueous MOH (M =
Li+, Na+, K+) are shown in Fig. 1a. It is obvious that the cathodic
and anodic peak potentials of spontaneous formed Ni(OH)2 shift to
positive slightly in the three alkali metal hydroxides with an order
of KOH b NaOH b LiOH, which is also evidenced by Anaissi et al.
[20], variation of potentials in these three electrolytes might be
caused by the possible interaction between OH− and alkali metal
cations. A scan rate study was carried out to understand the electrochemical
behavior of oxidized Ni films in strong alkaline medium,
and scan rates dependent cathodic and anodic peak currents are
shown in Fig. 1b. A linear relationship can be observed in Fig. 1b at
scan rates from10 to 200 mV s−1,which suggests an electrochemical
activity controlled by surface-bound redox species (Ni(OH)2 and
NiOOH), and current densities are very low compared to the case of
diffusion controlled. Meanwhile, peak-to-peak potential separations
in these three alkali electrolytes are close; there are 87 mV, 80 mV,
and 73 mV for 1 mol L−1 LiOH, NaOH, and KOH at scan rate
10 mV s−1, respectively