Selective electrochemical CO2 reduction over highly porous gold films†
Electrocatalytic reduction of CO2 to CO is usually subject to the competitive reduction of H+ to hydrogen. In this work, it was demonstrated that increasing the local pH at the electrode/electrolyte interface would greatly improve the selectivity for CO2 reduction to CO by inhibiting hydrogen evolution, resulting in a high CO faradaic efficiency of 90.5%. And this pH-induced effect can be achieved by increasing the thickness of the porous gold film through a facile synthetic technique, based on the enhancement of the mass transfer resistance within the highly porous electrode. Moreover, the thickest film, which had a large electrochemical surface area, displayed a significantly improved catalytic activity for CO2 reduction at a low overpotential of 390 mV. These results indicate that increasing the local pH by thickening the porous gold film is selective and efficient for electrochemical CO2 reduction.