Oscillatory dynamics during the methanol electrooxidation reaction on Pt(111)

Despite several papers describing the oscillatory methanol electrooxidation reaction (OMOR) catalyzed by polycrystalline Pt, these dynamic instabilities are less explored on single crystalline surfaces. Herein, we observed and mapped for the first time the OMOR on Pt(111) in non-adsorbing anion solutions as well as in the presence of small amounts of sulfate anions. Period 1 oscillations with oscillation frequencies from 1.2 to 2.0 Hz were observed for methanol concentrations higher than 1.0 M, with no evolution to more complex patterns. These oscillations occur in the potential range in which PtOH is partially covering the surface without irreversible oxidation processes. Small changes in both the mean potential (E_m) and the poisoning rate along the time-series were observed, the so-called drift, and were explained in terms of the accumulation of intermediates at the interface. The presence of sulfate strongly inhibits the OMOR, and the results are discussed in terms of sulfate adlayer formation on {111} domains.

Probing the surface fine structure through electrochemical oscillations

In the course of (electro)catalytic reactions, reversible and irreversible changes, namely the formation of adsorbed poisons, catalyst degradation, surface roughening, etc., take place at distinct time-scales. Reading the transformations on the catalyst surface from the measurement of the reaction rates is greatly desirable but generally not feasible. Herein, we study the effect of random surface defects on Pt(100) electrodes toward the electro-oxidation of methanol in acidic media. The surface defects are gently generated in situ and their relative magnitudes are reproducibly controlled. The system was characterized under conventional conditions and investigated under an oscillatory regime. Oscillatory patterns were selected according to the presence of surface defects, and a continuous transition from large amplitude/low frequency oscillations (type L) on smooth surfaces to small amplitude/high frequency oscillations (type S) on disordered surfaces was observed. Importantly, self-organized potential oscillations were found to be much more sensitive to the surface structure than conventional electrochemical signatures or even other in situ characterization methods. As a consequence, we proved the possibility of following the surface fine structure in situ and in a non-invasive manner by monitoring the temporal evolution of oscillatory patterns. From a mechanistic point of view, we describe the role played by surface defects and of the adsorbed and partially oxidized, dissolved species on the oscillations of type S and L.