Hydrogen Overpotential on Nickel in Alkaline Solution

Abstract

The exchange current, Tafel slope, stoichiometric number, and limiting anodic current of the hydrogen reaction on nickel in 0,1N NaOH depend on the pretreatment and the polarization history of the electrodes. The discharge step of the Volmer‐Tafel mechanism is rate‐determining on surfaces characterized by high fractional coverage with adsorbed hydrogen. Such surface states are metastable however and are transformed on anodic‐cathodic cycling to states which adsorb hydrogen weakly. The exchange currents for the discharge and combination steps are then about equal.