Metastable dual-defect states drive deep protonation for selective CO2 photomethanation

Efficient proton and charge carrier management is crucial in sustainable catalysis but is often constrained by the trade-off between proton supply kinetics and charge recombination, which limits selectivity. Here, we propose an in situ strategy to construct metastable adjacent dual-vacancy (MADV) sites, where dynamically tuned electronic states enable rapid electron transfer and spatial proximity ensures efficient mass transport, collectively enhancing proton-coupled electron transfer. Ti3d-derived active electronic states promote H2O dissociation, supplying abundant protons and forming hydroxylated surfaces for CO2 activation. Concurrently, dual-vacancy adjacency induces bidentate coordination, lowering the CO2 reduction barrier and steering selectivity toward CH4. The engineered MADV sites achieve nearly 100% CO2-to-CH4 selectivity with a production rate of 251.85 μmol g−1 h−1, approximately 75 times higher than pristine TiO2. These findings highlight the significance of adjacent sites with active electronic states in protonation processes and provide guidance for designing selective catalytic systems. This study reports a metastable dual-vacancy catalytic design that enhances proton-coupled electron transfer by balancing proton supply and charge separation. The system achieves nearly 100% CO₂-to-CH₄ selectivity with a 75-fold higher rate than pristine TiO₂, offering a new pathway for designing selective catalytic systems.