Selective CO ₂ ‐to‐CH ₄ Photoreduction Enabled by Au/TiO ₂ ‐ V _Ti Nanosheets via Boosting H ₂ O Dissociation and CO Protonation

ABSTRACT Photocatalytic CO ₂ methanation is fundamentally constrained by two intertwined bottlenecks: inefficient proton generation from H ₂ O dissociation and the premature desorption of the critical ^* CO intermediate. Here, we design metal cation vacancy clusters‐O ⁻ motifs for accelerating H ₂ O dissociation and boosting ^* CO protonation, while supported metal sites for CO ₂ activation over metal‐anchored metal oxide nanosheets. As a prototype, we fabricate Au/TiO ₂ ‐ V _Ti nanosheets, where synchrotron‐radiation X‐ray absorption fine structure and electron paramagnetic resonance spectroscopy confirm V _Ti ‐O ⁻ and coordination‐unsaturated Au sites. Density‐functional‐theory calculations reveal the creation of V _Ti ‐O ⁻ sites drive the step of ^* CO protonation toward ^* CHO from an endothermic process (0.09 eV) to an exothermic one (−0.29 eV), and concurrently the energy for H ₂ O dissociation into protons is lowered by a factor of two (1.31 eV → 0.65 eV). In situ Fourier‐transform infrared spectroscopy directly captures a distinct ^* CO intermediate, confirming its stabilization on the photocatalyst surface and thereby promoting the protonation step toward ^* CHO. Consequently, the Au/TiO ₂ ‐ V _Ti nanosheets show a superior CH ₄ formation rate of 156.5 µmol g ⁻¹ h ⁻¹ with near‐100% selectivity. Briefly, this work offers key insights into CO ₂ methanation bottlenecks and proposes a catalyst design blueprint to advance CO ₂ valorization.