Refining Defect States in W₁₈O₄₉ by Mo Doping: A Strategy for Tuning N₂ Activation towards Solar-Driven Nitrogen Fixation

Abstract

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.

Atomically Dispersed Molybdenum Catalysts for Efficient Ambient Nitrogen Fixation

“…Together with previous studies, [43][44][45] our work delivers fundamental experimental guidance for the design of efficient and robust catalysts for NH 3 synthesis under ambient conditions. Remarkably,t he as-fabricated electrocatalyst with an optimally high density of single Mo atoms anchored on NPC enables standout NRR performances,w hich provides an ew opportunity to develop advanced catalysts for N 2 fixation.…”

“…Notably,i fa ll this extra increased reduction current is used for the NRR under the N 2 -saturated environment (Figure 3a), the NH 3 yield rate at À0.3 Vversus RHE is calculated to be 119.6 mg NH 3 h À1 mg cat. [40][41][42] Moreover, 1 HNMR spectroscopy with isotope-labeled 15 N 2 [43] confirms that the ammonia detected in the NRR experiments was produced from the NRR ( Figure S17). À1 ).…”

Efficient Photocatalytic Nitrogen Fixation over Cuδ+‐Modified Defective ZnAl‐Layered Double Hydroxide Nanosheets

“…Peaks at 3555 and 3246 cm −1 can readily be assigned to asymmetric ν(NH) stretching modes of NH 3 . Similarly, peaks at 1740 and 1460 cm −1 are σ(HNH) bending vibration of NH 3 . The signal at 1648 cm −1 corresponds to an antisymmetric deformation vibration of NH 4 + 23a.…”

Recent Advanced Materials for Electrochemical and Photoelectrochemical Synthesis of Ammonia from Dinitrogen: One Step Closer to a Sustainable Energy Future

“…In 1977, Schrauze and co‐workers first discovered the photoreduction of N 2 by titanium dioxide (TiO 2 ) in an aqueous solution, introducing new opportunities for photocatalytic NH 3 synthesis over semiconductor photocatalysts under low temperatures and ambient pressures . Since then, various materials have been prepared for the application of NRR, such as metal oxide/sulfide, g‐C 3 N 4 , Bi‐based photocatalysts, layered double hydroxides, etc . Nevertheless, the photochemical N 2 reduction systems face challenges such as the problematic collection and recovery of photocatalysts after multiple cycles, sluggish surface reaction dynamics and possible reverse reactions.…”