The electrooxidation of carbon monoxide on platinum as examined by surface infrared spectroscopy under forced hydrodynamic conditions

Abstract

A flow-cell arrangement for FTIR spectroelectrochemical studies involving continuous or periodic replenishment of the thin-layer solution is described, and applied to the pseudo steady-state electrooxidation of solution carbon monoxide at platinum electrodes in 0.1 M HClO 4. Unlike potential-difference infrared spectra obtained using a conventional stagnant thin layer, substantial CO coverages θ CO (as deduced from the intensity of the terminal C-O stretching band) are maintained to relatively positive electrode potentials (ca. 1.0 to 1.2 V vs. Ag/AgCl) in the presence of continuous solution flow. Similar results are obtained following positive-going potential steps and slow potential sweeps. Corresponding current-potential data indicate that facile electrooxidation of solution CO occurs at potentials where high CO coverages are observed ( θ CO ~ 1), although the fastest rates are obtained at more positive potentials where θ CO <1. The results, although unexpected, are not inconsistent with the conventional mechanism featuring a rate-determining reaction between adsorbed CO and adjacent hydroxyl (or water) species. These results are compared and contrasted briefly with corresponding data for methanol and formic acid electrooxidation. The virtues of such continuous flow measurements involving known and adjustable thin-layer thicknesses are pointed out.