Tracking oxygen atoms in electrochemical CO oxidation - Part I: Oxygen exchange via CO2 hydration

We report a new method to measure the kinetic rate constant of CO2 hydration using electrochemical oxidation of carbon monoxide (CO oxidation) in isotope-labeled electrolyte. CO oxidation is often used as a model reaction to investigate the surface of metallic electrocatalysts, most notably in CO stripping experiments. Using chip-based electrochemistry mass spectrometry with O-18-labeled electrolyte we show that: 1) For CO stripping experiments on Pt, one oxygen in the product CO2 comes from the reactant CO and the other comes from the electrolyte, consistent with the Langmuir-Hinshelwood mechanism involving the adsorbates *CO and *OH . 2) Some of the formed CO2 subsequently exchanges oxygen with the elec-trolyte via short-lived carbonic acid. We use the time-dependent isotopic ratios to calculate the kinetic reaction rate constant of the CO2 hydration reaction and compare it to literature. By doing this at two different temperatures we show that the method is robust and that O-18-labeled CO stripping experiments provide an accurate measurement of the rate constant for CO2 hydration. Chip-based electrochemistry mass spectrometry combined with isotopic labeling is thus shown to be a versatile and powerful tool for elucidating mechanistic aspects of homogeneous reactions as well as electrocatalytic reactions. (C) 2021 Elsevier Ltd. All rights reserved.