A non-equivalent Ni doped La-MOF for enhanced photocatalytic CO2 reduction through oxygen vacancy regulation and electronic structure optimization

Abstract

Photocatalytic CO₂ reduction holds promise for mitigating global warming and achieving carbon neutrality. Metal–organic frameworks (MOFs) are particularly promising as photocatalysts due to their ability to tune metal–oxo cluster electronic structures and facilitate CO₂ adsorption. In this study, a chemically stable La-MOF modified with Ni-doped metal–oxo clusters has been synthesized through a one-pot solvothermal reaction. Experimental and in situ test results show that the introduction of Ni atoms leads to the formation of oxygen vacancies (VOs) induced by the unsaturated coordination of La/Ni-MOF, which facilitates the adsorption and activation of CO₂. The electronic structure of metal–oxo (La–O) clusters is also effectively regulated, which enhances the electron-accepting ability of La–O clusters and promotes the photo-induced electron transfer from the lowest unoccupied molecular orbital (LUMO) of the electron donor to the conduction band (CB) of La-MOF. In addition, the built-in metal atom (Ni) acts as an active site for CO₂ adsorption and activation, achieving effective charge transfer and activated CO₂ adsorption integrated construction. Interestingly, LSV electrochemical tests showed that the onset potential of the La/Ni-MOF-3 electrode in the CO₂ bubbling system was lower than that of the N₂ bubbling system, indicating that CO₂ reduction proceeds preferentially to H₂ reduction. The synergy of these effects leads to the optimal La/Ni-MOF with a CO selectivity of 96.8% and a yield of 669.3 μmol g⁻¹, which is 2.5-fold and more than 5-fold as high as that of the pure La-MOF and Ni-MOF, respectively. This work provides a facile but efficient strategy for the construction of coordination unsaturated metal sites and VOs as well as the regulation of the electronic structure of MOFs as efficient photocatalysts towards enhanced performances.