Rates of adsorption, desorption, and oxidation of CO on PEM electrodes

The rates of CO adsorption, desorption, and oxidation on proton exchange membrane fuel cells (PEMFC) electrodes are determined. Desorption was controlled by the parallel desorption of CO from linear bridge bonded sites and rearrangement between them. The kinetic rate constant for rearrangement from linear to bridge bonding is 3 to 4 orders of magnitude higher than either of the two desorption rate constants. Adsorption was significantly influenced by convection of the gas along the flow channel and diffusion of CO into the catalyst layer. Oxidation of preadsorbed layer of CO followed a dual path mechanism as well. However, rearrangement between the two types of bonding was negligible since the time duration of CO oxidation was 2 to 3 orders of magnitude smaller than the desorption time. Hence oxidation rates were determined by the sum of two exponential terms corresponding to linear and bridge bonded CO molecules.