Tracking Oxygen Atoms in Electrochemical CO oxidation - Part II: Lattice Oxygen Reactivity in Oxides of Pt and Ir

Abstract Electrochemical oxidation of carbon monoxide (CO oxidation) is often used as a model reaction to investigate the surface of metallic electrocatalysts, most notably in CO stripping experiments. In this report, we use chip-based electrochemistry mass spectrometry with 18 O isotope-labeled oxides Pt and Ir to investigate the involvement of lattice oxygen in the electrochemical oxidation of water (the oxygen evolution reaction, OER), adventitious carbon, and CO. For Pt, we find that the labeled oxygen from Pt 18 O x is incorporated into the CO 2 resulting from CO oxidation at the potential at which oxygen at the electrode surface is reduced to hydroxyl ( * OH), confirming that * OH is the reactive species in the Langmuir-Hinshelwood electrochemical oxidation of CO. For Ir we find that lattice oxygen in Ir 18 O 2 is similarly involved in electrochemical CO oxidation, but only if it is first activated by a reductive sweep. The labeled CO 2 signal is transient, indicating that activated lattice oxygen provides the “ignition sites” for the Langmuir-Hinshelwood electrochemical oxidation of CO on Ir. We also confirm the previously reported result that electrochemically prepared, amorphous, Ir 18 O x incorporates much more lattice oxygen in O 2 evolved during OER than does rutile Ir 18 O 2 , but we also quantify the amount and show that in all cases the labeled O 2 is a very small portion of the total O 2 evolved, and that more lattice oxygen is released in CO 2 when oxidizing CO and adventitious carbon than is released in O 2 when oxidizing water. Through these results, we demonstrate that EC-MS in concert with isotope labeling and CO as a probe molecule can provide insight into lattice oxygen reactivity, extending the utility of CO oxidation to the study of noble metal oxides used in e.g. PEM electrolyzer anodes.