Low Bandgap NiCo ₂ S ₄ Nanoparticles Decorated 2D‐BiOBr Nano Pallets: Atomic Level Insight into the Active Sites for Photocatalytic H ₂ O ₂ Production

2D-BiOBr (BOB) has recently gained great potential for harvesting solar light and its applications for photocatalysis. However, the lack of active sites with adequate reduction potential has become one of the major challenges in this regard. In this work, a unique heterojunction hybrid has been designed by decorating low band gap NiCo₂S₄ Nanoparticles (NCS) on BOB nanopallets (NCS@BOB) for efficient photocatalytic H₂O₂ production. Detailed characterizations suggest that the composite material possesses better surface properties with higher oxygen defects (OVs), enhance visible-light absorption capability, the ability for effective photogenerated charge separation through intimate heterojunction, etc. Periodic PBE-D calculations have been carried out to complement the experimental findings in detail. The optimized photocatalyst displayed a maximum H₂O₂ production rate of 9.67 mmg_cat. ^-1 in 2 hr, which is 3.3 times higher than the pristine BOB. Further experiments unveil the mechanism of photocatalytic H₂O₂ production. Results confirm that it follows a dual-step two-electron transfer pathway for oxygen reduction reaction (ORR), with obvious superoxide formation as an intermediate step. Computational calculations critically explain the synergistic role of both "Ni" and "Co" centers as active sites for overall photocatalysis.