Elementary reaction steps in C1 electrooxidation

The detailed mechanistic understanding of the electrooxidation of the C1 molecules methanol, formaldehyde and formic acid represents a considerable challenge because of the presence of com­peting reaction pathways and their subtle dependence on the reaction conditions; despite numer­ous studies and considerable progress in specific aspects, a coherent and generally accepted mechanistic picture is still missing. This project aims at a fundamental understanding of the elementary reaction steps during the oxidation reaction, focusing on Pt electrodes. This shall be reached by systematic spectro-electrochemical studies and a close interaction between theory (P5) and experiment, where theory should indicate also measurable observables that allow to discriminate between different possible reaction mechanisms.

The objective shall be reached in two ways, in a direct way, including the identification / characteri­zation of reaction intermediates not detected hitherto and the evaluation of kinetic isotope effects (KIEs) in specific reaction steps, and in an indirect way, which is essentially based on the system­atic evaluation of the effect of variations in experimental parameters such as potential, temperature, pH value/anions, reactant concentration on the kinetics of well-defined elementary reaction steps (e.g., COad formation) and comparison with trends derived from theory (P5). Information on the nature of new adsorbed reaction intermediates, which had been detected in the first period, and their temporal evolution at different reaction conditions shall be obtained from highly sensitive in situ IR spectroscopy measurements in an attenuated total reflection geometry (ATR-FTIRS).

The kinetics of well defined reaction steps, e.g. the formation/removal of reaction intermediates, and their variation with reaction conditions shall be determined from time-resolved ATR-FTIRS and/or DEMS (differential electrochemical mass spectrometry) measurements, including fast measurements in the ms to s regime, upon changing between differently labeled reactants or from reactant-free to reactant-containing electrolyte. In combination with theory, kinetic isotope effects in these reactions and their variation with reaction conditions allow conclusions on the barrier shape and hence on the dynamics of the rate determining step, and its variation. Additional measurements using single crystal film /single crystal electrodes are planned to unravel structural effects.

Finally, the data derived from this work together with data derived in collaborating groups inside and outside the research group and data present in the literature shall be assembled in a coherent reaction network for C1 oxidation on Pt, which allows to assess the contributions of the different reaction pathways under different, defined reaction conditions. Important aspect here is to clearly point out the range of reaction conditions for certain mechanistic claims, which so far has often been neglected.