Allowing for charge distributions in reagents (products) when analyzing electrostatic effects in electrochemical kinetics

Application of the slow-discharge theory for analyzing experimental data on the electron transfer kinetics in the cases where the charge is distribute d nonuniformly over species of the reagent and/or product is considered. It is shown that, for real reagents whose size in some cases is commensurate with characteristic thicknesses of the diffuse part of EDL, the corrected T afel dependences (CTD) cannot be interpreted on the basis of the approximat ion of point reagents. In particular, CTD constructed with ordinary techniq ues are expected to be linear near the potential of zero charge (PZC). Subs tantial errors may also arise when heterogeneous rate constants are determi ned by extrapolating CTD. At the same time, the charge distribution makes n o impact on the reagent charge in the bulk solution calculated with the Fru mkin-Petrii equation. Deviations of CTD from linearity caused by the above effects are the strongest near PZC and substantially differ from those pred icted by the Marcus theory for point reagents. In a wide range of potential s (electrode charges), charge distributions of reagents and products do not affect the apparent transfer coefficient. However, they may substantially alter the rate constant derived by extrapolating CTD. Special cases of char ge distributions modeling reactions that involve complex anions, functional ly substituted organic molecules, and anion-cation pairs are considered.