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-CO 2 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. The electrocatalytic Ethanol-to-CO 2 selectivity is quantitatively probed, obtaining the FE C1 value of 45–80% and 3–15% in alkaline and acidic media, respectively. • Replenishing EOR dual-pathway mechanism by ATR-SEIRAS and IRAS. • Revealing that Ir-H ad species are from the ethanol dissociation. • Estimation of quasi-quantitative FE C1 based on multiple methods. • FE C1 on Ir is up to 80% at low potentials in acidic media.