Unassisted Highly Selective Gas-Phase CO₂Reduction with a Plasmonic Au/p-GaN Photocatalyst Using H₂O as an Electron Donor

Surface plasmon resonances in metal nanostructures enable the generation of nonequilibrium hot electron-hole pairs, which has received wide interest as a means to drive chemical reactions at the nanoscale. However, harvesting hot holes in plasmonic heterostructures to drive oxidation reactions to balance the photocatalytic CO2 reduction reaction has been challenging. Further, details of the balanced redox reaction pathways for gas-phase photocatalysis have been difficult to identify. Here, we report an Au/p-GaN plasmonic heterostructure photocatalyst in which unassisted, self-sustaining, highly selective photocatalytic CO2 reduction to CO is directly balanced by water oxidation, operating under solar illumination. We find remarkable enhancements in CO yield for heterostructures that employ a metal/insulator/semiconductor configuration with an ultrathin aluminum oxide layer between composite Au/Cu nanoparticles and p-GaN. Our work underscores the potential for plasmonic heterostructure photocatalysts to perform selective and unassisted gas-phase photocatalytic CO2 reduction to convert solar energy into chemical fuels.