Uranium-Doped Induced 5f‑π Orbital Hybridization Promotes CO₂ Reduction to C₂₊ Products on MXenes (M = Ti, Zr, Hf) Monolayers

Photocatalytic CO₂ reduction into high-value C₂₊ products is quite exciting but challenging since the transition paths of photogenerated electron and excited-state active sites during photocatalysis are still. Herein, we investigated the process of reducing CO₂ in uranium-doped M₃C₂O₂ 0 materials (M = Ti, Zr, and Hf) from the perspectives of detailed interfacial structure evolution and reaction mechanism. Among the three materials and four models, UHf₃C₂O_2x–1 exhibits the best CO₂ photoreduction performance with a CO yield of 273.44 μmol·g^–1, 2.4 times higher than that of Hf₃C₂O_2x–1 (113.67 μmol·g^–1). In-depth experimental and theoretical studies reveal that the doping of tetravalent uranium plays a crucial role in the activation of CO₂. The effective orbital hybridization between the U f_z³ orbital and the CO₂ Π* molecular orbital induces electron spin polarization, which significantly reduces the activation energy. The mechanism of *CHO coupling occurs in the process of UHf₃C₂O_2x–1 catalyzing the formation of C₂₊ products, which has a significantly lower energy barrier than that of the traditional *CO coupling process. This interpretation indicates that adjusting the oxidation state of uranium can tune the electronic structure and catalytic performance of the UM₃C₂O_2x–1. This work provides novel insights into the behavior of f-electrons in the reaction mechanism and predicts catalysts containing uranium.