Surface (Electro)chemistry of CO₂ on Pt Surface: An <i>in Situ</i> Surface-Enhanced Infrared Absorption Spectroscopy Study

Understanding the surface (electro)­chemistry of CO₂ and CO on Pt is needed to design active, selective catalysts for CO-tolerant fuel cell reactions and CO₂ reduction. In this work, the surface reactivity of Pt in a CO₂-saturated alkaline electrolyte was revealed by combining <i>in situ</i> surface-enhanced infrared absorption spectroscopy (SEIRAS) with density functional theory (DFT) calculations. We show that during potential cycling in 1 M KHCO₃ electrolyte, CO adsorbates (CO_ad), more specifically, CO_ad surrounded by OH adsorbates (OH_ad), with linear or bridged configuration, were produced through the reductive adsorption of HCO₃^– catalyzed by H adsorbates on Pt. The CO_ad coadsorbed with OH_ad was oxidized to COOH_ad at potentials as low as ∼0.3 V_RHE, which was further oxidized to CO₂ at 0.9 V_RHE and higher. Further analysis suggests that the proximity between CO_ad and OH_ad is key to trigger the conversion reaction from CO_ad to CO₂ through forming COOH_ad intermediate at room temperature. The details about how Pt surface adsorbates change as a function of voltage in CO₂-saturated alkaline electrolytes can provide strategies to design CO-tolerant catalysts for fuel cell applications and active and selective catalysts for the CO₂ reduction reaction