Photonic–Plasmonic–Quantum Synergistic Effect on PtAu/SiO ₂ Catalyst Performance

Photonic architecture enables precise control of the light–matter interactions in photocatalysis. However, designing structures that simultaneously enhance light harvesting, improve charge transfer efficiency, and maintain catalytic stability remains a formidable challenge. Here, we engineer a 3D catalyst by embedding Pt–Au nanoparticles within SiO2 opals, where simulation-guided tuning of opal periodicity generates partial photonic band gaps to couple with the Au surface plasmon resonance (SPR). The optimized catalyst (Pt–Au/SiO2-opal) yields a 12-fold local electromagnetic field enhancement. Using methanol dehydrogenation as a two-electron probe reaction to isolate hot carrier dynamics, we achieved a 45-fold increase in the methanol dehydrogenation rate (194 μmol g–1 h–1, >99.8% HCHO selectivity) compared to bulk PtAu/SiO2 (4.3 μmol g–1 h–1). Embedding Pt, both as electron mediators and active site within a quantum-confined, multidirectional opal scaffold, improves Au hot-carrier generation and funnels charge through directional interfacial channels. The fluence-independent cooling dynamics and extended carrier lifetimes unambiguously break the two-temperature model (TTM), establishing photonic-plasmonic coupling as a route to catalytic regimes beyond the thermal limit.