Heptanuclear Cadmium Borovanadate Containing a Sandwich-Type Anionic Partial Structure {B20V12} as a Heterogeneous Photocatalyst for the Reduction of CO2 into CH4

The novel heptanuclear cadmium borovanadate [Cd(en)3]{[Cd(H2O)(en)]6[B20V12O60(OH)2]}·8H2O (en = ethylenediamine) has been prepared under hydrothermal condition. It exhibits a 2D layered architecture that is built up from the [Cd(H2O)(en)]2+ coordination cations and new sandwich-type borovanadate anions [B20V12O60(OH)2]14- constructed by BO3, BO4, BO3(OH), and VO5 units. It features the first heptanuclear cadmium borovanadate containing the single valence of V4+ cations and unique B/V ratio (B/V = 20/12). Its thermal, magnetic, XPS, and optical properties have been systematically studied. The Eg (2.60 eV), EVB (1.69 eV), and ECB (-0.91 eV) were well determined by the UV-vis diffuse reflectance spectrum, UPS curve, and the formula ECB = EVB - Eg, respectively. The photocatalytic experiments revealed that the borovanadate could be selected as an effective and stable heterogeneous catalyst for the reduction of CO2 to CH4 by means of visible light (the amount for CH4 gas could reach 50.57 μmol·g-1·h-1 when the reaction time was 3 h). The recycling experiment and photocatalytic mechanism were also well investigated and established in detail.

Dynamic and Reversible Blending Interface on Polyoxovanadate Electrode for High-Performance Lithium-Ion Batteries

Solid electrolyte interphase (SEI) plays a critical role in the performance of lithium-ion batteries (LIBs). In contrast to the clear interface between the traditional consecutive electrode materials and SEI, ionic polyoxometalates (POMs) as electrode could bilaterally diffuse with SEI and form a blending interface for superior electrochemical performance. POMs have recently aroused much interest as electrode materials in LIBs due to their structural flexibility, high capacity, and cycling stability. However, the interface evolution between POM-based electrodes and SEI, which is critical for Li+ ion transportation, has rarely been explored. Herein, we choose Li10[V12B18O60H6] (LVB) as an example to investigate the formation and structural evolution of the electrode-electrolyte interface. Time-of-flight secondary ion mass spectrometry together with X-ray photoelectron spectroscopy demonstrates the evolution of a blending layer at the interface containing typical SEI components, a polyanion from LVB and a phosphate anion from decomposition products of LiPF6. In the blending layer, ion migration takes place between the P-related inorganic species and the polyanion during the Li+ insertion/extraction reaction. Such a compatible blending layer favors Li+ transportation and the reversibility of the redox reactions, as supported by a series of electrochemical analyses. This work provides detailed insights into understanding the interface evolution of the LVB electrode and demonstrates the importance of interfacial engineering to induce proper interface layers in the development of high-performance POM-based electrodes for LIBs.

Water assisted high proton conductance in a pure-inorganic framework vanadoborate

A pure-inorganic framework vanadoborate is successfully synthesized under hydrothermal conditions and exhibits good proton conductivity.

Efficient proton conductivity of a novel 3D open-framework vanadoborate with [V6B20] architectures

A new three-dimensional (3-D) inorganic metal-oxygen network vanadoborate Na3H10[Ni(H2O)2(VO)6(B10O22)2]·NH4·19H2O (1) constructed from lantern-type {(VO)6(B10O22)2} clusters, NaO6 polyhedra and NiO6 octahedra, was successfully synthesized by a hydrothermal method. In the structure, the {V6B20} clusters are linked together through NiO6 octahedral bridges, resulting in 1-D chains along the c-axis. The 1-D chains are further connected by NaO6 polyhedra to give rise to a 3-D open-framework structure. Furthermore, lots of NH4+ and H2O molecules are accommodated in the void of the structure, and may interact with the [V6B20] system via N-HO, O-HO hydrogen bonds, constructing a complex hydrogen-bonding network system. Strikingly, compound 1 exhibited a high proton conductivity of 3.22 × 10-3 S cm-1 at 50 °C under 100% RH with an activation energy of 1.66 eV.

Vanadoborates: cluster-based architectures, preparation and properties

The different connections of [VO_x] (x = 4, 5, 6) and [AO_x] (A = B, x = 3, 4; A = P, x = 4) polyhedral units ultimately result in a fascinating variety of vanadoborate anionic clusters.

Study on the source of magnetic properties of three novel boratopolyoxovanadates via two-dimensional infrared correlation spectroscopy

Three novel polyoxovanadoborates namely [V₁₂B₁₈O₄₆(OH)₁₄(H₂O)_0.75]·20.5H₂O 1, Na₂[V₁₂B₁₈O₄₈(OH)₁₂(H₂O)_0.5]·26.5H₂O 2 and Cd_0.5{[Na(H₂O)₂]2[Na(H₂O)]₂[Na(H₂O)₃]2V₁₂B₁₈O₅₃(OH)₇(H₂O)_0.5}·11H₂O 3 have been hydrothermally synthesized and structurally characterized. The boratopolyoxovanadate cage [V₁₂B₁₈O₆₀] backbones in 1-3 are constructed by the combination of two hexameric oxovanadate units [V₆O₉] and one puckered [B₁₈O₄₂] ring via sharing O atoms. All three compounds were obtained under alkaline conditions, and the cluster anions were all [V₁₂B₁₈O₆₀]. But the cations were different, it is inferred that the protonation of the three compound cluster ions is different, respectively [V₁₂B₁₈O₄₆(OH)₁₄(H₂O)_0.75] in 1, [V₁₂B₁₈O₄₈(OH)₁₂(H₂O)_0.5]^2- in 2 and [V₁₂B₁₈O₅₃(OH)₇(H₂O)_0.5]^7- in 3. The V oxidation states ratio of V^IV to V^V were 2:1 confirmed by valence bond calculation and XPS. We studied the magnetic properties of three compounds by two methods: The variable temperature magnetic susceptibility and the 2D IR COS under magnetic perturbation. From the 2D IR COS under magnetic perturbation map, it is showed that all three: (1) the presence of V^IV. (2) Certain quasi-aromaticity from B₃O₃ six-membered ring. (3) The difference of protonation and the charge of the cluster anions. This work enriches the theory of two-dimensional correlation spectroscopy and also provides a new approach to the study of magnetic materials.

The origin of the electronic transitions of mixed valence polyoxovanadoborates [V12B18O60]: from an experimental to a theoretical understanding

New insights in the electronic properties of mixed-valence polyoxovanadoborate clusters.

Proton conduction in a new 3-D open-framework vanadoborate with an abundant hydrogen bond system

A 3-D hydrogen bond-enriched vanadoborate was successfully synthesized under hydrothermal conditions and it exhibited good proton conductivity.