Bandgap Engineering and Oxygen Vacancies of NixV₂O5+x (x = 1, 2, 3) for Efficient Visible Light‐Driven CO₂ to CO with Nearly 100% Selectivity

It is difficult to design a new single‐component photocatalyst to simultaneously possess a bandgap small enough to absorb most of sunlight and strong redox ability to reduce CO 2 into value‐added chemical fuels. Herein, bandgap engineering of nickel vanadate compounds (Ni x V 2 O 5+ x , x = 1, 2, 3) is rationally designed to overcome the above challenge. Through changing the Ni:V ratio, the bandgap and band edge positions of nickel vanadates can be regulated, enabling Ni 2 V 2 O 7 and Ni 3 V 2 O 8 to reduce CO 2 in the presence of water under visible light irradiation that do not exist in NiV 2 O 6 . Ni 3 d orbitals of Ni 2 V 2 O 7 and Ni 3 V 2 O 8 replace V 3 d orbitals of NiV 2 O 6 and hybridize with O 2 p orbitals to form the valence band maximums, resulting in their negative shifts. Meanwhile, the relatively weaker effect of the crystal field in VO 4 tetrahedron over Ni 2 V 2 O 7 and Ni 3 V 2 O 8 results in less V 3 d split, thus making the conduction band edges to shift upward. In addition, higher concentration of oxygen vacancies over Ni 2 V 2 O 7 can further enhance its photocatalytic activity for CO 2 conversion into CO with nearly 100% selectivity by prolonging the lifetime of photogenerated carriers and improving the chemisorption of CO 2 .