Electrocatalytic ethanol-to-CO2 selectivity on the Ir electrode: A quasi-quantitative electrochemical infrared absorption spectroscopic investigation

Ir has long been regarded as an alternative ethanol-to-CO₂ electrocatalyst, but little is known about the ethanol oxidation reaction (EOR) mechanism on Ir, especially the C1 pathway selectivity. Thereby, in situ quasi-quantitative electrochemical infrared absorption spectroscopy (QEIAS), consisting of total-reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), infrared absorption spectroscopy (IRAS), and transmission infrared absorption spectroscopy (TIAS) with a thin-layer flow cell, is established to probe it. Initially, the well-accepted EOR dual-pathway mechanism is confirmed via ATR-SEIRAS and IRAS. Ir-H_ad species (ca. 2040 cm⁻¹), originating from the ethanol dissociation at low potentials, are observed for the first time to replenish the reaction process. Based on it, the apparent Faradaic efficiency of the C1 pathway (FE_C1) is readily estimated to be as high as 76.4% (0.7 V) in acidic media. The quantitative analysis of reaction residual verifies these FE_C1 results through high-performance liquid chromatography (HPLC), and a relative error of only 2–9% exists between the two methods. Thus, Ir might be more efficient for ethanol complete oxidation than other Pt-group metallic catalysts, especially in acidic media. This work could be necessary for the rational design of Ir-based EOR catalysts with high C1 pathway selectivity and low over-potential for direct ethanol fuel cells.