Reversibility of platinum voltammograms in aqueous electrolytes and ionic product of water

Abstract

Well-known reversibility of platinum voltammograms in supporting aqueous electrolytes formally contradicts the equilibrium defined by the ionic product of water: K w = [H +]·[OH −] ≅ 1 × 10 −14, since at any pH value, concentration one of these ions in solution should be too low (≤10 −7 M) to ensure reversibility of voltammograms in the whole potential region of investigation at usual potential scan rates. This contradiction could be overcome by allowing dissociative water adsorption. There are no direct experimental proofs of this process on platinum, however all available relevant data obtained by in situ physical methods appear to provide indirect evidences for this hypothesis.