Surface (Electro)chemistry of CO2 on Pt Surface: An in Situ 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 in situ 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 (COad), more specifically, COad surrounded by OH adsorbates (OHad), with linear or bridged configuration, were produced through the reductive adsorption of HCO3- catalyzed by H adsorbates on Pt. The COad coadsorbed with OHad was oxidized to COOHad at potentials as low as similar to 0.3 V-RHE, which was further oxidized to CO2 at 0.9 V-RHE and higher. Further analysis suggests that the proximity between COad and OHad is key to trigger the conversion reaction from COad to CO2 through forming COOHad 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.