Uranium-Doped Induced 5f- 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, UHf(3)C(2)O2(x-1) exhibits the best CO2 photoreduction performance with a CO yield of 273.44 mu mol center dot g-1, 2.4 times higher than that of Hf3C2O2x- 1 (113.67 mu mol center dot 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 fz 3 orbital and the CO2.* molecular orbital induces electron spin polarization, which significantly reduces the activation energy. The mechanism of *CHO coupling occurs in the process of UHf(3)C(2)O(2)x- 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 UM(3)C2(O)2(x-1). This work provides novel insights into the behavior of f-electrons in the reaction mechanism and predicts catalysts containing uranium.