Refining electronic properties of Bi2MoO6 by In-doping for boosting overall nitrogen fixation via relay catalysis

Modern agriculture and the chemical industries rely heavily on ammonia and nitrate-based products. However, the classic Haber-Bosch and Ostwald processes are extremely energy-consuming and environmentally damaging. Herein, we proposed In-doped Bi2MoO6 photocatalyst to achieve "overall nitrogen fixation" via relay catalysis (N2→NH3/NH4+→NO3-). Density functional theory (DFT) supported the partial substitution of Bi3+ with In3+ in Bi2MoO6. The density of states further testified that In3+ doping has significantly altered the d-band center, achieving a lower energy barrier for N2 chemisorption/activation and the subsequent hydrogenation reaction at the H2O/In-doped Bi2MoO6 interface. The experiment revealed that using N2 and H2O as feedstock, 5% In-Bi2MoO6 realized 1.4 folds higher charge-carrier density under illumination with expedited spatial separation/transfer and extended charge-carrier lifespan compared to Bi2MoO6. The photocatalyst attained the NH3 production rate of 53.4 μmol·g–1·h–1 at 5% In-Bi2MoO6, which was 13-fold higher than Bi2MoO6 (4.1 μmol·g–1·h–1) while the NO3- production rate reached 54 μmol·g–1·h–1. This work overcame the thermodynamic barrier of N2 being first reduced to NH3/NH4+, then further oxidized to NO3- products, realizing "overall nitrogen fixation", opening a new avenue toward developing clean, energy-saving, and cost-effective ammonia and nitrate production.