Plasmon-Induced Hot Carriers for Photocatalytic CO₂ Reduction with Au/p-GaN Heterostructures

The production of solar fuels from H₂O, sunlight, and CO₂ is an intriguing approach to achieve a sustainable society. Surface plasmon resonances (SPR) in metal nanostructures that can harvest sunlight and generate non-equilibrium hot carriers capable of catalyzing chemical reactions offer an appealing material platform for solar fuel generators. Harvesting hot holes in plasmonic-semiconductor heterostructures to drive oxidation reactions and balance the reduction reaction has been especially promising. We realized a Au/p-GaN heterostructure based plasmonic device which can perform photocatalytic water oxidation reaction and CO₂ reduction to CO with high selectivity under solar illumination, without external bias, in a gas phase operation condition. The balanced redox reaction pathways were validated with photoreductive deposition and labeled isotope experiments. We also studied the effect of interfacial layer and co-catalysts incorporation. Extended carrier life time with oxide passivation of surface trap states indicating efficient hot hole injection from Au nanoparticles into p-GaN is supported by transient absorption measurement. Co-catalysts facilitating charge transfer and utilization for catalytic reaction is also examined. An optimized device composed of plasmonic light absorber (Au), hot hole extractor (p-GaN), ultrathin interfacial passivation layer (Al₂O₃), and efficient co-catalysts (Cu) all together result in over 300% enhancement of CO generation rate than the Au/p-GaN case. This result as an outlook shows the plasmonic heterostructure platform can be further improved for self-sustaining artificial photosynthesis.