Ammonia (NH3) is essential for fertilizer production and is increasingly recognized as a promising carbon-free energy carrier. Given the abundant energy input from solar illumination and the widespread availability of relatively inexpensive atmospheric nitrogen (N2) gas, photocatalytic N2 fixation has attracted an increasing amount of interest. Here, we report a bismuth-rich design strategy within the Bi-O-Br system to enhance the photocatalytic N2 fixation. A series of bismuth oxybromides with tunable Bi/Br ratios (BiOBr (1:1) to Bi4O5Br2 (2:1), Bi24O31Br10 (2.4:1), and Bi3O4Br (3:1)) were synthesized by a facile solvothermal route and evaluated for N2 reduction in pure water under visible light without cocatalysts or sacrificial agents. Among them, Bi3O4Br achieved the highest NH3 yield (790 μmol/g/h) and exhibited good structural stability, retaining more than 95% of its activity over three repeated cycles. The efficient activity is attributed to its stronger light absorption, more negative conduction band, efficient charge separation, and longer carrier lifetime. Spectroelectrochemical analysis confirmed its high reduction ability, while oxygen vacancies facilitated enhanced N2 adsorption and bond cleavage. Selectivity is evidenced by NH3 being the only detected nitrogen-containing reduction product in the postreaction solution, and concurrent water oxidation is evidenced by H2O2 formation. These results establish a clear composition-activity relationship, highlighting bismuth-rich Bi3O4Br as a practical and effective photocatalyst for the fixation of aqueous N2 into NH3.
Kheradmand et al. (Tue,) studied this question.