ESCA Studies of Electrode Surfaces

Abstract

Film or adsorbed layer formation on an electrode surface has a marked effect on the behavior of that electrode. A redistribution of charge and potential occurs at the interfaces giving rise to double-layer regions. The ability of the film to transport material and charge will have important effects. The formation of the film may involve new electrode reactions; for example, for a metal M we may have \( M \to {{M}^{{2 + }}} + 2e \) but formation of an oxide film is possible via the reaction \( M + {{H}_{2}}O \to 2{{H}^{ + }} + M - O + 2e \) It is not surprising to find, therefore, that the formation of a film on the electrode surface has a marked effect on the current—voltage curves for the electrode system concerned. For example, Figure 1 shows the current—voltage curve for a smooth platinum electrode in 0.5 mol dm−3 sulfuric acid.(1) As the potential is increased, the current falls initially due to oxidation of hydrogen on the electrode (formed in the return process). The current then rises sharply due to oxide formation prior to oxygen evolution (which occurs at the cusp on the extreme right-hand side of Figure 1). On decreasing the potential the current rises sharply due to oxide reduction, and then falls, rising again, with peaks due to adsorbed hydrogen formation prior to hydrogen evolution (which occurs at the cusp on the extreme left-hand side of Figure 1).