Nanoporous Au Thin Films on Si Photoelectrodes for Selective and Efficient Photoelectrochemical CO2 Reduction

An Si photoelectrode with a nanoporous Au thin film for highly selective and efficient photoelectrochemical (PEC) CO2 reduction reaction (CO2RR) is presented. The nanoporous Au thin film is formed by electrochemical reduction of an anodized Au thin film. The electrochemical treatments of the Au thin film critically improve CO2 reduction catalytic activity of Au catalysts and exhibit CO Faradaic efficiency of 96% at 480 mV of overpotential. To apply the electrochemical pretreatment of Au films for PEC CO2RR, a new Si photoelectrode design with mesh‐type co‐catalysts independently wired at the front and the back of the photoelectrode is demonstrated. Due to the superior CO2RR activity of the nanoporous Au mesh and high photovoltage from Si, the Si photoelectrode with the nanoporous Au thin film mesh shows conversion of CO2 to CO with 91% Faradaic efficiency at positive potential than the CO2/CO equilibrium potential. Si photoelectrode with a nanoporous Au thin film is proposed for highly selective and efficient photoelectrochemical (PEC) CO2 reduction reaction (CO2RR). The nanoporous Au thin film by electrochemical pretreatments exhibits critically improved CO2 reduction activity. For PEC CO2RR, an Si photoelectrode combined with mesh‐type nanoporous Au co‐catalysts achieves 91% CO2 conversion selectivity at positive potential than the CO2/CO equilibrium potential.