Room Temperature COad Desorption/Exchange Kinetics on Pt Electrodes-A Combined In Situ IR and Mass Spectrometry Study

The room temperature desorption and exchange of CO in a saturated CO adlayer on a Pt electrode, at potentials far below the onset of oxidation, was investigated by isotope labeling experiments, using a novel spectroelectrochemical setup, which allows the simultaneous detection of adsorbed species by in situ IR spectroscopy and of volatile (side) products and reactants by online mass spectrometry under controlled electrolyte flow conditions. Time‐resolved IR spectra show a rapid, statistical exchange of pre‐adsorbed 13COad by 12COad in 12CO containing electrolyte; mass spectrometric data reveal first‐order exchange kinetics, with the rate increasing with CO partial pressure. The increasing COad desorption rate in equilibrium with a CO containing electrolyte is explained by a combination of an increasing COad coverage upon increasing the CO pressure, and a decrease of the CO adsorption energy with coverage, due to repulsive COad–COad interactions. Desorption and exchange of CO: The exchange of a saturated 13CO adlayer by gas‐phase 12CO is monitored by in situ attenuated total reflection infrared spectroscopy (ATR–IR) spectroscopy and online mass spectrometry (see figure). First‐order exchange and the dependence of the exchange rate on the partial pressure of 12CO indicate COad desorption at room temperature and a desorption‐controlled exchange mechanism.