New opportunities for efficient N2 fixation by nanosheet photocatalysts

Promoting photocatalytic nitrogen fixation with alkali metal cations and plasmonic nanocrystals

Photocatalytic nitrogen fixation can produce ammonia from nitrogen and water under ambient conditions in the presence of sunlight. Here, we report that alkali metal cations (Li⁺, Na⁺, and K⁺) can significantly promote nitrogen activation and plasmonic nanocrystals (Au and Ag) can sensitize photocatalysts under visible light. The ammonia yield and selectivity on Au/P25 under UV-vis irradiation could be increased from 0.085 mmol g^-1 h^-1 and 75% to 0.43 mmol g^-1 h^-1 and 94.5% when promoted by K⁺, showing a visible-light-driven activity of 0.14 mmol g^-1 h^-1 and an AQE of 0.62% at 550 nm. The activity could be further increased to 1.02 (UV-vis) and 0.32 (visible) mmol g^-1 h^-1 with AQE of 0.93% at 550 nm with methanol added as the sacrificial agent. This strategy could be applied to a series of photocatalysts (e.g. TiO₂, ZnO, and BiOBr) and may represent a general approach for designing efficient nitrogen fixation processes.

Tuning Oxygen Vacancies in Ultrathin TiO2 Nanosheets to Boost Photocatalytic Nitrogen Fixation up to 700 nm

Dinitrogen reduction to ammonia using transition metal catalysts is central to both the chemical industry and the Earth's nitrogen cycle. In the Haber-Bosch process, a metallic iron catalyst and high temperatures (400 °C) and pressures (200 atm) are necessary to activate and cleave NN bonds, motivating the search for alternative catalysts that can transform N₂ to NH₃ under far milder reaction conditions. Here, the successful hydrothermal synthesis of ultrathin TiO₂ nanosheets with an abundance of oxygen vacancies and intrinsic compressive strain, achieved through a facile copper-doping strategy, is reported. These defect-rich ultrathin anatase nanosheets exhibit remarkable and stable performance for photocatalytic reduction of N₂ to NH₃ in water, exhibiting photoactivity up to 700 nm. The oxygen vacancies and strain effect allow strong chemisorption and activation of molecular N₂ and water, resulting in unusually high rates of NH₃ evolution under visible-light irradiation. Therefore, this study offers a promising and sustainable route for the fixation of atmospheric N₂ using solar energy.

Tuning the catalytic activity of a single Mo atom supported on graphene for nitrogen reduction via Se atom doping

Electrochemical nitrogen (N2) fixation as an effective method has realized the sustainable production of ammonia where efficient electrocatalysts for converting N2 into NH3 at room temperature have become a key scientific issue. Herein, we proposed that the catalytic activity of a single Mo atom supported on graphene (Mo/G) for the nitrogen reduction reaction (NRR) can be tuned by non-metal heteroatom (B, N, P, S, Se etc.) doping. Our density functional theory (DFT) calculations revealed that the Se atom is the best doping element to tune the optimal electronic structure of the Mo atom for catalyzing the NRR among these heteroatoms, leading to the lowest potential of 0.41 V vs. RHE for Mo/SeG, which is much better than the current metal-based catalysts. Our work provided a new strategy to design electrocatalysts for the NRR.