In-situ anion exchange based Bi2S3/OV-Bi2MoO6 heterostructure for efficient ammonia production: A synchronized approach to strengthen NRR and OER reactions

ABSTRACT Photocatalytic ammonia generation via nitrogen reduction reaction (NRR) is a green and prospective nitrogen fixation technique. However, NRR is often hampered by the high N2 adsorption/activation energies and is accompanied by a slow kinetics oxygen evolution reaction (OER). Herein, a robust Bi2S3/OV-Bi2MoO6 S-scheme heterojunction is constructed using a simple in-situ anion exchange process, which enables oxygen vacancy (OVs) abundant Bi2MoO6 microspheres with surface deposited Bi2S3. The as-fabricated Bi2S3/OV-Bi2MoO6 functioned as an effective photocatalyst to convert N2-to-NH3 under mild conditions. The photocatalytic NH3/NH4+ production rate reached 126 μmol gcat−1 under visible light for 2.5 h with 2% of Bi2S3/OV-Bi2MoO6 photocatalyst, which was 8-fold higher than pristine Bi2MoO6. Furthermore, the as-fabricated Bi2S3/Bi2MoO6 heterojunction exhibited good selectivity, high stability and reproducibility. The excellent photocatalytic NRR performance was ascribed to the Bi2S3/Bi2MoO6 heterojunction formed subsequent to the strong interaction between Bi2S3 and Bi2MoO6. The OVs facilitated the chemical adsorption process allowing activation of N2 molecule on the Bi2S3/Bi2MoO6. Simultaneously, the S-scheme heterojunction prolonged the lifetime of photogenerated carriers, accelerated the electrons/holes spatial separation and accumulation on the Bi2S3 (reduction) and Bi2MoO6 side (oxidation), respectively, thus strengthening both OER and NRR half-reactions. This simple in-situ anion exchange method offers a novel technique for strengthening OER and NRR half-reactions in Bi-based photocatalysts for effective photocatalytic ammonia generation.