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Photocatalytic nitrogen reduction reaction (NRR) is a sustainable process for ammonia synthesis under mild conditions. However, photocatalytic NRR activity and are generally limited by inefficient carrier separation and transfer. Therefore, parallel engineering of bulk phase doping and surface coupling is critical to achieving the goal of efficient NRR. In this study, Cl doped BiOBr nanosheet assemblies (BiOBr/Cl) were constructed in delicately designed deep eutectic solvents (DESs), combined with ionothermal methods at low temperatures and Bi 3+ exsolution reduction strategy at high temperatures. The unique liquid state and reducibility of DESs induce the reduction of Bi 3+ and the in situ coupling of Bi quantum dots at the surface of BiOBr/Cl nanosheets along with the construction of Bi-BiOBr/Cl nanosheet assemblies. The experimental results show that Cl doping could reduce the exciton dissociation energy and promote its dissociation to free carriers. Bi quantum dots could form tightly coupled Schottky junction with BiOBr/Cl enabling the efficient and unidirectional transmission of photogenerated electrons from BiOBr/Cl to metal Bi. The formed electron deficient region at Schottky interface promotes the adsorption and activation of N 2 . The hierarchical structure of Bi-BiOBr/Cl nanosheet assembly benefits to providing more N 2 adsorption active sites. The DFT calculation shows that the accumulation of high concentration of active hydrogen in Bi-BiOBr/Cl leads to a significant decrease of energy barrier of the first step hydrogenation of N 2 . Bi-BiOBr/Clis more inclined to adsorb nitrogen for NRR in comparison with H* for hydrogen production. The synergistic effect of Cl doping and Bi coupling result in a high NRR activity of Bi-BiOBr/Cl photocatalyst of 6.67 mmol·g -1 ·h -1 , which was 11.3 times higher than that of initial BiOBr. This study provides a promising strategy for designing highly active NRR photocatalysts with high efficiency carrier dissociation and transport., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)