Polyoxometalate-based nanocomposites with electrocatalytic activity have been applied in hydrogen evolution reactions (HER). Seawater as the main water resource on the earth should be developed as the water electrolysis to prepare high-purity hydrogen. In this paper, we used two synthesis strategies to prepare the nanocomposite Co₄-POM@Co-PGDY (Co₄-POM: the Kegging-type microcrystals of K₁₀[Co₄(PW₉O₃₄)₂] and Co-PGDY: cobalt-porphyrin linked graphdiyne) with excellent activity for HER. Co-PGDY as the porous material is applied not only as the protection of microcrystals towards the metal ion in seawater but also as the co-electrocatalyst of Co₄-POM. Co₄-POM@Co-PGDY exhibits excellent HER performance in seawater electrolytes with low overpotential and high stability at high density. Moreover, we have observed a key H₃O⁺ intermediate emergence on the surface of nanocomposite during hydrogen evolution process in seawater by Raman synchrotron radiation-based Fourier transform infrared (SR-FTIR). The results in this paper provide an effective strategy for preparing polyoxometalate-based electrocatalysts with high-performance toward hydrogen evolution reaction.

In this study, a new {Co₉} cluster-added polyoxometalate (POM) Cs₃K₄Na₅H₆[BO(OH)₂Co₉O(OH)(H₂O)₃(GeW₆O₂₆)(B-α-GeW₉O₃₄)₂]·22H₂O (1) was successfully synthesized in the presence of inorganic boron sources under hydrothermal conditions. Its structural characterizaiton is realized using single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Compound 1 represents the first Co-added POM bonded by a B atom, and its polyoxoanion is constructed by fusing together with one hexalacunary GeW₆O₂₆ and two trilacunary B-α-GeW₉O₃₄ fragments in an unprecedented V-shaped {Co₉} cluster. Additionally, compound 1 is an efficient catalyst for accelerating the Knoevenagel condensation of various aldehydes with malonitrile.

An acentric hexa-Ti-oxo-cluster-added trimeric phosphotungstate, [H₂N(CH₃)₂]₃H₁₂[Ti₆O₆(A-α-1,2-PW₁₀O₃₇)₃]∙12 H₂O (1), was synthesized by reacting trivacant polyoxometalate (POM) fragments with Ti⁴⁺ ions under hydrothermal conditions and characterized via single-crystal/powder X-ray diffraction, solid UV–vis and IR spectroscopies, and thermogravimetric analysis. The polyoxoanion of 1 is constituted by three Ti₂O₃(A-α-1,2-PW₁₀O₃₇) subunits linked through Ti–O–Ti bonds, forming a ring-shaped configuration. Furthermore, 1 exhibits a second-harmonic generation response about 0.6 times that of KH₂PO₄, which paves the way toward the development of Ti-added POMs in the field of nonlinear optical materials.

Cluster-based functional materials have made remarkable progress owing to their wonderful structures and distinctive physicochemical performances, one of on-going advancements of which is basically driven by synthetic chemistry of exploring and constructing novel nanosized gigantic polyoxometalate (POM) aggregates. In this article, an unprecedented nanoscale hexameric arsenotungstate aggregate Na₉K₁₆H₄[Er_0.5K_0.5(H₂O)₇][Er₅W₁₀O₂₆(H₂O)₁₄][B-α-AsW₉O₃₃]₆·102H₂O (1) has been synthesized by the combined synthetic strategy of simultaneously using the arsenotungstate precursor and simple tungstate material in a highly acidic aqueous solution. The {[Er₅W₁₀O₂₆(H₂O)₁₄][B-α-AsW₉O₃₃]₆}³¹⁻ polyanion in 1 consists of an intriguing dumbbell-shaped pentadeca-nuclear W–Er heterometal {Er₅W₁₀O₂₆(H₂O)₁₄}²³⁺ cluster connecting six trilacunary [B-α-AsW₉O₃₃]⁹⁻ moieties, which has never been seen previously. Furthermore, through electropolymerization of 1 and pyrrole on the conductive substrate, a thickness-controllable and robust 1–PPY (PPY = polypyrrole) hybrid film was successfully prepared, which represents the first POM–PPY film assembled from high-nuclear lanthanide (Ln) encapsulated POM and PPY hitherto. The 1–PPY film-based electrochemical biosensor exhibits a favorable recognition performance for ochratoxin A in multiple media. This work not only provides a feasible combined synthetic strategy of the POM precursor and simple tungstate material for constructing complicated multi-Ln-inserted POM aggregates, but also offers a promising electrochemical platform constructed from POM-based conductive films for identifying trace biomolecules in complex environments.