Unassisted Highly Selective Gas-Phase CO₂ Reduction 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.