Effect of pressure and temperature on carbon dioxide reduction at a plasmonically active silver cathode

Abstract

Carbon dioxide (CO2) reduction at a plasmonically active silver cathode was investigated by varying the pressure and temperature at multiple applied potentials under both dark and illuminated conditions to understand the mechanism of selectivity changes driven by plasmon-enhanced electrochemical conversion. CO2 partial pressures (PCO2) from 0.2 to 1 atm were studied during linear sweep voltammetry and chronoamperometry at −0.7, −0.9, and −1.1 VRHE. At a given applied overpotential the total current density increased with increasing PCO2 in both the dark and the light, but there were significant differences in the Tafel behavior between dark and illuminated conditions. The reduction of CO2 to carbon monoxide (CO) was found to have first-order behavior with respect to PCO2 at all applied potentials in both the dark and the light, likely indicating no change in the rate-determining step upon illumination. Activity for the hydrogen (H2) evolution reaction decreased with increasing PCO2 at slightly different rates in the dark and the light at each applied potential, making it unclear if light is influencing CO or H2 intermediate adsorbate coverage. Both formate and methanol production showed no dependence on PCO2 under any conditions, but the true reaction orders may be masked by the much higher activity for CO and H2 at the silver cathode. The investigation of product distribution with temperature at 14, 22, and 32∘C at −0.7, −0.9, and −1.1 VRHE in both the dark and the light demonstrated that the selectivity changes observed upon illumination are not caused by local heating of the cathode surface.