Quantifying desorption and rearrangement rates of carbon monoxide on a PEM fuel cell electrode

Abstract

A simple procedure to quantify the rates of carbon monoxide (CO) desorption from, and simultaneous rearrangement on, supported platinum fuel cell electrode (Pt on Vulcan XC-72R) is reported. The surface coverage of CO on Pt electrode in equilibrium with bulk CO was measured from the anodic peaks in the CO stripping voltammogram. The decline in these surface coverages due to desorption and rearrangement, once CO was replaced by N 2 in the gas phase was recorded and used in conjunction with a kinetic model to quantify the respective rates. Two distinct CO oxidation peaks observed in the voltammogram due to the oxidation of two distinct ad-species, namely weakly and strongly adsorbed CO ( C O ad I and C O ad II ), were baseline corrected and deconvoluted using a bimodal Gaussian distribution. Saturation surface coverage of C O ad I decreased with increasing temperature, while the opposite was true for C O ad II . Rearrangement from C O ad II to C O ad I was faster than the desorption rate of either CO species. The desorption rate of C O ad II was at least an order of magnitude lower than that of C O ad I molecules at all temperatures studied. The activation energies for desorption of C O ad I and C O ad II were estimated to be 24.08 and 27.99 kJ/mol, respectively. The activation energy for rearrangement from C O ad I to C O ad II was 35.23 kJ/mol and that from C O ad II to C O ad I was 27.55 kJ/mol.