An unprecedented polyoxometalate-based 1D double chain compound with opposite charges enables conductivity improvement

Metal-metal bonded pentamolybdate hybrids as electron storage materials

Two electron-rich, metal-metal bonded pentamolybdate hybrids, 2D-[MoIV3MoVI2O10Sr2(H2O)5(C6H4O7)2py3]·3.5H2O (1) and 1D-[MoIV3MoVI2O10Sr(H2O)3(C6H4O7)2py3]·py·2[NH2(CH3)2]·2H2O (2, py = pyridine), were prepared by the partial solvothermal oxidation of [MoIV3O2(O2CCH3)6(H2O)3]ZnCl4·8H2O and citric acid in py/H2O (for 1) or py/H2O/DMF (for 2). Both 1 and 2 feature a triangularly metal-metal bonded incomplete cuboidal [MoIV3O4] unit. Redox-active 6e-[MoIV3O4] units can serve as an "electron sponge" to store/release six electrons reversibly via Δ-bond breakage and re-formation during charging/discharging processes. 1 and 2 further form 3D and 2D supramolecular structures, respectively, through slipped π-π stacking interactions between the pyridine ligands. Both the incorporated 6e-redox active [MoIV3O4] unit and the 3D/2D supramolecular conductive networks in hybrid-POM 1/2 remarkably enhance the electronic conductivity and reversible multi-electron redox ability with the structural integrity retained. Consequently, 1 and 2 exhibited high discharge specific capacities of 236.0 and 277.0 mA h g-1 at 50 mA g-1, respectively, and a good cycling performance at high current density (121.8 mA h g-1, 2 A g-1 for 2), providing a new way for improving POM-based electrode materials.

An inorganic-organic hybrid nanomaterial with a core-shell structure constructed by using Mn-BTC and Ag5[BW12O40] for supercapacitors and photocatalytic dye degradation

Creating inorganic-organic hybrids with polyoxometalates (POMs) and metal-organic frameworks (MOFs) as energy storage and dye-degradation materials remains challenging. Here, a new hybrid nanomaterial Mn-BTC@Ag₅[BW₁₂O₄₀] is synthesized by using Ag₅[BW₁₂O₄₀] and Mn₃(BTC)₂(H₂O)₆ (Mn-BTC, BTC = 1,3,5-benzenetricarboxylic acid) through a plain grinding method. The structure and morphology characterization by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and transmission electron microscopy (TEM) shows that the synthetic products have core-shell construction. Due to its unique structure wherein the core is Mn-BTC and the shell is Ag₅[BW₁₂O₄₀], it exhibits excellent capacitance performance. In a three-electrode system where nickel foam is a collector, at a current density of 1 A g^-1, its specific capacitance is 198.09 F g^-1; after 5000 cycles, the capacitance retention rate is 94.4%. When the power density is 503.1 W kg^-1, the symmetrical supercapacitor reveals a high energy density which is 10.9 W h kg^-1. At the same time, the capacitance retention is 92.9% after 5000 cycles which showed good cycle stability. The photocatalytic degradation efficiencies of rhodamine B (RhB), methyl orange (MO) and methylene blue (MB) dyes exceed 90% after 140 min, and the degradation results remained unchanged after five photocatalytic cycles. The photocatalytic degradation mechanism shows that ˙OH has a major effect. The results show that this research provides a fresh idea for the development of energy storage and dye photocatalytic degradation materials.

Four POM-based complexes modified by multi-nuclear clusters: structures, photocatalytic, supercapacitor and chromogenic properties

Four POM-based complexes were synthesized under hydrothermal conditions by using two kinds of triazole derivatives, namely [Cu2(Cmt)2(OH)Cl(β-Mo8O26)0.5] (1), [Cu(H2O)3(H3/2Tpm)2](HTpm)(PMo12O40)2·4H2O (2), [Cu3Cl2(H2Tpm)2(HTpm)4(PMo12O40)4]·26H2O (3), [Co3(HTpm)6(H2O)2(Mo13O42)2]·21H2O (4) (Cmt = 1-cyclopropylmethyl-1-H-[1,2,4]triazole, Tpm = 4-(3-[1,2,4]triazole-4-propyl)morpholine)....