Integration of CO₂ activation and photogenerated electron accumulation at Ti site via dual-tandem electric fields in BiOBr-MIL-125 heterojunction for boosting CO₂ photoreduction

The rational design of heterojunction photocatalysts is crucial for enhancing CO₂ photoreduction efficiency, yet precisely channeling photogenerated electrons to the CO₂ adsorption sites remains an enormous challenge. In this work, we developed an organic-inorganic heterostructure with continuous inter- and intra-component electric fields. The integration of BiOBr with MIL-125 via chemical bonding established a heterojunction, where the built-in electric field between the two components facilitated the efficient transfer of photogenerated electrons from BiOBr to MIL-125. The intrinsic electric field of MIL-125 further drove the accumulation of photogenerated electrons at Ti sites. This tandem electric field effect, in conjunction with the CO₂ adsorption and activation at Ti sites, significantly enhanced the efficiency of CO₂ reduction within the heterojunction system. The optimized photocatalyst achieving CO production at a rate of 65.6 μmol g⁻¹ h⁻¹ with nearly 90 % selectivity without the use of sacrificial agents, exhibiting a remarkable 43-fold and 8-fold enhancement in activity compared to pristine MIL-125 and BiOBr, respectively. In-situ infrared spectroscopy and theoretical calculations confirmed the energy optimization effect of the heterostructure on CO₂ activation and the hydrogenation reaction, facilitating the formation of the key intermediate *COOH. This work elucidates the mechanism by which tandem built-in electric fields facilitate charge separation.