Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N chemisorption at active sites (e.g., surface defects), the N molecules have yet to receive energetic electrons toward efficient activation and dissociation, often forming a bottleneck. Herein, we report that the bottleneck can be well tackled by refining the defect states in photocatalysts via doping. As a proof of concept, WO ultrathin nanowires are employed as a model material for subtle Mo doping, in which the coordinatively unsaturated (CUS) metal atoms with oxygen defects serve as the sites for N chemisorption and electron transfer. The doped low-valence Mo species play multiple roles in facilitating N activation and dissociation by refining the defect states of WO: (1) polarizing the chemisorbed N molecules and facilitating the electron transfer from CUS sites to N adsorbates, which enables the N≡N bond to be more feasible for dissociation through proton coupling; (2) elevating defect-band center toward the Fermi level, which preserves the energy of photoexcited electrons for N reduction. As a result, the 1 mol % Mo-doped WO sample achieves an ammonia production rate of 195.5 μmol g h, 7-fold higher than that of pristine WO. In pure water, the catalyst demonstrates an apparent quantum efficiency of 0.33% at 400 nm and a solar-to-ammonia efficiency of 0.028% under simulated AM 1.5 G light irradiation. This work provides fresh insights into the design of photocatalyst lattice for N fixation and reaffirms the versatility of subtle electronic structure modulation in tuning catalytic activity.

Photocatalytic conversion of CO to CH, a carbon-neutral fuel, represents an appealing approach to remedy the current energy and environmental crisis; however, it suffers from the large production of CO and H by side reactions. The design of catalytic sites for CO adsorption and activation holds the key to address this grand challenge. In this Article, we develop highly selective sites for photocatalytic conversion of CO to CH by isolating Cu atoms in Pd lattice. According to our synchrotron-radiation characterizations and theoretical simulations, the isolation of Cu atoms in Pd lattice can play dual roles in the enhancement of CO-to-CH conversion: (1) providing the paired Cu-Pd sites for the enhanced CO adsorption and the suppressed H evolution; and (2) elevating the d-band center of Cu sites for the improved CO activation. As a result, the PdCu-TiO photocatalyst achieves the high selectivity of 96% for CH production with a rate of 19.6 μmol g h. This work provides fresh insights into the catalytic site design for selective photocatalytic CO conversion, and highlights the importance of catalyst lattice engineering at atomic precision to catalytic performance.