The free-base porphyrin, 5,10,15,20-tetrakis( 1-methyl-4-pyridyl)-21H,23H-porphine (H2TMPyP), adsorbs onto a basal-plane graphite electrode. Under DC cyclic voltammetric conditions, the fully protonated dication, [H4TMPyP(0)](2+), undergoes an apparently close to ideal surface-confined two-electron reduction to the neutral [H4TMPyP(-II)] species when the supporting electrolyte consists of aqueous 1 M HCl and 1 M NaCl and coverages are sub-monolayer. The reversible potential calculated from the average of the oxidation and reduction peak potentials is 0.138 +/- 0.002 V (vs Ag/AgCl, 3 M NaCl) whilst their separation Delta E-p approaches 0mV at slow scan rates, as expected theoretically for an ideal surface-confined electron transfer process. Comparisons of simulated and experimental data imply that the increase in Delta E-p observed at scan rates above 10Vs(-1) is consistent with uncompensated Ohmic IRu drop effects, and not limitations imposed by electron transfer kinetics. Analysis of fundamental and higher harmonic components derived from large-amplitude sine-wave AC voltammetry is consistent with a very fast electron transfer rate constant, k(0), in excess of 10(6) s(-1) for the overall two-electron process. However, careful comparison with AC theory highlights minor levels of non-ideality not attributable to purely capacitative background on uncompensated resistance effects. These are particularly evident when greater than monolayer-surface coverages are employed. It is likely that subtle contributions from heterogeneity in the adsorbed layer and complexities in the reaction mechanism are present in this close to ideal surface-confined process, but they are more readily detected under conditions of large-amplitude Fourier transformed AC cyclic voltammetry than with the conventionally used DC cyclic format. (C) 2008 Elsevier Ltd. All rights reserved.