Electro-oxidation of surface β-Ni(OH)2 residing on metallic Ni to β-NiOOH was studied in 0.5 M aqueous KOH at 277 K ≤ T ≤ 318 K by means of cyclic voltammetry (CV) and chrono-amperometry (CA). The process is accompanied by a diffusion of H+ within the surface oxide phase. The formation of β-NiOOH gives rise to an anodic peak in CV profiles, the potential of which depends on the scan rate (s). An analysis of the relation between the anodic peak current density (j peak, AN) and s indicates that the growth of β-NiOOH is controlled by the diffusion of H+ and its modelling leads to the determination of the diffusion coefficient of H+ (D(H+)). In the case of 277 K ≤ T ≤ 318 K, the values of D(H+) are of the order of 10–11 cm2 s–1, when calculated with respect to the electrode’s geometric surface area (A geom), and of the order of 10–12 cm2 s–1, when calculated with respect to the electrochemically active surface area (A ecsa). The activation Gibbs energy of H+ diffusion (Δdiff G ≠(H+)) is in the 19.5–22.6 kJ mol–1 range. Chrono-amperometry transients for the formation of β-NiOOH are analyzed on the basis of finite-space diffusion, with the assumption that β-NiOOH can be formed through three mechanistic pathways. The values of D(H+) determined for both A geom and A ecsa using this approach are of the order of 10–12 cm2 s–1. They are smaller than the analogous values of D(H+) determined on the basis of CV measurements but the values of Δdiff G ≠(H+) obtained using these two experimental approaches are comparable