Electron transfer reaction through an adsorbed layer

Electron transfer from a redox to an electrode through an adsorbed intermediate is considered in this paper. The formalism is developed to cover all regimes of coverage factor, from lone adsorbate to monolayer regime. The randomness in the distribution of adsorbates is handled using coherent potential approximation. Current–overpotential profile for all coverage regime is provided. Explicit analysis of the low and high coverage regime is done by supplementing with the density of states (dos) profile for adsorbate in both weak and strongly coupled sectors. The prominence of bonding and anti-bonding states in the strongly coupled adsorbates at low coverage gives rise to saddle point behaviour in the current–overpotential profile. The variation of current with overpotential at low coverage is consistent with the Marcus inverted region prediction and the traditional direct electron transfer behaviour at high coverage is recovered through the present analysis.

► Formalism developed to handle electron transfer for all value of medi-ating adsorbate coverage. ► CPA used to handle randomness in distribution of adsorbates. ► Marcus inverted regime is obtained at low coverage. ► High coverage electron transfer mimics to direct electron transfer. ► Anodic and cathodic current expression are compared.