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

• Published in: Electrochimica Acta
• Main Authors: Scott, Søren B., Kibsgaard, Jakob, Vesborg, Peter C.K., Chorkendorff, Ib
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Kinetics; CO2 hydration; CO oxidation; DEMS; Mechanisms; Langmuir; Carbonic acid
• Online Access: https://orbit.dtu.dk/en/publications/bc531bd6-dd31-40a5-b427-f0d7b1dd6fba; https://doi.org/10.1016/j.electacta.2021.137842; https://backend.orbit.dtu.dk/ws/files/240712608/COox_I_H2CO3_revised.pdf

We report a new method to measure the kinetic rate constant of CO 2 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 18 O-labeled electrolyte we show that: 1) For CO stripping experiments on Pt, one oxygen in the product CO 2 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 CO 2 subsequently exchanges oxygen with the electrolyte via short-lived carbonic acid. We use the time-dependent isotopic ratios to calculate the kinetic reaction rate constant of the CO 2 hydration reaction and compare it to literature. By doing this at two different temperatures we show that the method is robust and that 18 O-labeled CO stripping experiments provide an accurate measurement of the rate constant for CO 2 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.