Bandgap Engineering and Oxygen Vacancies of Ni_xV₂O_5+x (x = 1, 2, 3) for Efficient Visible Light‐Driven CO₂ to CO with Nearly 100% Selectivity

Abstract

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 CO2 into value‐added chemical fuels. Herein, bandgap engineering of nickel vanadate compounds (NixV2O5+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 Ni2V2O7 and Ni3V2O8 to reduce CO2 in the presence of water under visible light irradiation that do not exist in NiV2O6. Ni 3d orbitals of Ni2V2O7 and Ni3V2O8 replace V 3d orbitals of NiV2O6 and hybridize with O 2p orbitals to form the valence band maximums, resulting in their negative shifts. Meanwhile, the relatively weaker effect of the crystal field in VO4 tetrahedron over Ni2V2O7 and Ni3V2O8 results in less V 3d split, thus making the conduction band edges to shift upward. In addition, higher concentration of oxygen vacancies over Ni2V2O7 can further enhance its photocatalytic activity for CO2 conversion into CO with nearly 100% selectivity by prolonging the lifetime of photogenerated carriers and improving the chemisorption of CO2.

Unlocking the significance of high H2O resistance for nickel vanadate phases to improve the kinetic parameters or consequences of catalytic NOX reduction and poison pyrolysis

“…1F). 29–32 V 5+ cations trapped in [VO 4 ] 3− subunits are coordinatively unsaturated and lead to the inclusion of one and two open V 5+ species in a per unit cell for Ni 1 V 2 O 6 and Ni 2 V 2 O 7 /Ni 3 V 2 O 8 , respectively. 29–32 This suggested that SO Z 2− -functionalized Ni 2 V 2 O 7 /Ni 3 V 2 O 8 could surpass the Ni 1 V 2 O 6 analogue in resisting H 2 O or in activating the redox cycle.…”

“…29–32 V 5+ cations trapped in [VO 4 ] 3− subunits are coordinatively unsaturated and lead to the inclusion of one and two open V 5+ species in a per unit cell for Ni 1 V 2 O 6 and Ni 2 V 2 O 7 /Ni 3 V 2 O 8 , respectively. 29–32 This suggested that SO Z 2− -functionalized Ni 2 V 2 O 7 /Ni 3 V 2 O 8 could surpass the Ni 1 V 2 O 6 analogue in resisting H 2 O or in activating the redox cycle. This could tentatively result from Ni 1 V 2 O 6 with the smallest amount of O V species acting as H 2 O binding spots and O M reservoirs, if nickel vanadates were defect-free and featured by identical binding strengths with H 2 O/O 2 .…”

“…5–8,23,24 This could be combined with dissimilar crystallographic traits of Ni 1 V 2 O 6 /Ni 2 V 2 O 7 /Ni 3 V 2 O 8 (Fig. 1F) 29 to pose the necessity for regulating the synthetic conditions of the SO 2 /O 2 -modified catalysts in an identical fashion. In this regard, TiO 2 -supported nickel vanadates (Ni 1 /Ni 2 /Ni 3 ) were synthesized by following the identical wet impregnation protocols except for altering the molar Ni : V ratios of 1 : 1–3 : 1, across which V contents were set to 2 wt% because of its ubiquity found in previous SCR articles reported elsewhere.…”

“…1F). 29,30 Hence, in the sole ground of the XPS spectra in the V 2p regimes, it was challenging to predict the nickel vanadate with the largest concentration of LA (or O V ) sites utilized to immobilize SO Z 2− functionalities, bind with H 2 O, or afford O M species.…”

“…Ni 1 V 2 O 6 , Ni 2 V 2 O 7 , and Ni 3 V 2 O 8 are synthetically viable 29,30 and have promising H 2 O tolerance under SCR environments and are thereby implemented as catalytic phases, deposited on TiO 2 , and functionalized with SO Z 2− to produce Ni 1 –S, Ni 2 –S, and Ni 3 –S, respectively. Ni 1 V 2 O 6 was also dispersed on Sb-promoted TiO 2 and modified with SO Z 2− for the formation of Ni 1 –Sb–S owing to the ample justifications specified below.…”