Mechanism of methanol photoelectrooxidation on titanium dioxide thin film electrodes

The title reaction has been studied by measuring the transient photocurrents observed in the early stages of illumination. Transients and steady state photocurrents measured at different applied potentials and methanol concentrations were compared with the numerical calculations of the differential equations corresponding to several possible mechanisms. Excellent fittings were obtained on the assumption that surface hole trapping as -OH' mediates the charge transfer to methanol. Formation of -OH' accounts for the high initial photocurrents and their rapid decay; the slow oxidation of 'OCH3 to OCH2 gives rise to an increase at longer times, after a minimum transient photocurrent is observed. Alternative, kinetically equivalent, mechanisms are either less likely, or involve a larger number of fitting parameters.