The Reversible Redox Behaviour of Adsorbate Layers on Account of the Electrosorption Valency

The electrosorption valency γ [9-11] was introduced regarding acid-base and redox equilibria at low surface concentrations at excess supporting electrolyte. A formula is given for the calculation of the apparent protolytic dissociation constant of an adsorbate (Eq. (10)) and a modified Nernst equation for adsorbates being to some extent immersed in a compact double layer (Eq. (17)). Neglecting the integral term another formula was obtained for the pH dependence of the half-wave (peak) potentials of reversible surface redox reactions (Eq. (18)). Also modified equations for the peak current (Eq. (23)) and peak width (Eq. (24)) of cyclic voltammograms involving adsorbed species were deduced. Test substances were Pyocyanine, Nile blue and Neutral red adsorbed at graphite electrodes.