During utilizing structural and functional advantages of polyoxometalates (POMs) for enhanced applications, the suitable assembly of these clusters in framework materials acting as the binding nodes represents one of the mostly favourable approaches. In contrast to well-developed coordination/covalent combinations, a convenient strategy to build the porous structures of POMs with smaller sized counterions as bridging ligand via ionic interaction is developed here to reinforce the capability in gas adsorption in parallel to MOFs/COFs. With this goal, a series of POMs-based ionic

Dendrite growth and side reactions of Zn metal anodes remain unresolved obstacles for practical application of aqueous Zn ion batteries. Herein, a two-dimensional (2D) organic−inorganic heterostructure with controlled thickness was constructed as a protective layer for a Zn metal anode. The reduction of uniformly distributed polyoxometalate in the layer causes a negative charge density gradient, which can accelerate zinc ion transfer, homogenize zinc deposition, and shield sulfates at the electrode interface, while the exposed hydrophobic alkyl chain of the layer can isolate the direct contact of water with the Zn anode. As a result of the synergetic effect, this 2D organic−inorganic heterostructure enables high Zn plating/stripping reversibility, with high average Coulombic efficiencies of 99.97% for 3700 cycles at 2 mA cm −2 . Under high Zn utilization conditions, a high arealcapacity full cell with hundreds of cycles was demonstrated.

Figure 6. The electrochemical behavior of full cells with the mixed electrolyte. a) CV profiles of Zn||MnO 2 cells at different scan rates from 0.1 to 2 mV s −1 with 75% ZnSO 4 electrolytes; b) plots of log(peak current, mA) versus log(scan rate, mV s −1 ) at specific peak currents extracted from the CV scans; c) contribution ratio of pseudocapacitive at different scan rates; d) Long-term cycle performance of Zn||MnO 2 battery at 1 A g −1 with different electrolytes; SEM images of Zn anode after Zn||MnO 2 cells test with e) 75% ZnSO 4 , f) ZnSO 4 , and g) Zn(OTF) 2 electrolyte.

Counter-cations are essential components of polyoxometalates (POMs), which have a distinct influence on the solubility, stabilization, self-assembly, and functionality of POMs. To investigate the roles of cations in the packing of POMs, as a systematic investigation, herein, a series of triol-ligand covalently modified Cu-centered Anderson-Evans POMs with different counter ions were prepared in an aqueous solution and characterized by various techniques including single-crystal X-ray diffraction. Using the strategy of controlling Mo sources, in the presence of triol ligand, NH4+, Cu2+ and Na+ were introduced successfully into POMs. When (NH4)6Mo7O24 was selected, the counter cations of the produced POMs were ammonium ions, which resulted in the existence of clusters in the discrete state. Additionally, with the modulation of the pH of the solutions, the modified sites of triol ligands on the cluster can be controlled to form δ- or χ-isomers. By applying MoO3 in the same reaction, Cu2+ ions served as linkers to connect triol-ligand modified polyanions into chains. When Na4Mo8O26 was employed as the Mo source to react with triol ligands in the presence of CuCl2, two 2-D networks were obtained with {Na4(H2O)14} or {{Na2(H2O)4} sub-clusters as linkers, where the building blocks were δ/δ- and χ/χ-isomers, respectively. The present investigation reveals that the charges, sizes and coordination manners of the counter cations have an obvious influence on the assembled structure of polyanions.

The shuttling effect of soluble polysulfides and the inadequate conductivity of sulfur and lithium sulfide impede the practical utilization of lithium–sulfur batteries. To address this issue, the polar δ-MnO2 nanosheets with a 2D morphology can provide abundant anchor and catalytic sites for polysulfides. However, the poor intrinsic conductivity restricts the transformation ability. Herein, we introduce mixed Mn4+/Mn3+ valence states in δ-MnO2 nanosheets by a facile annealing method to promote the redox kinetics of polysulfides. This treated MnO2 maintains its 2D morphology, providing abundant absorption sites for polysulfides, while the introduction of mixed valence states enhances charge transfer and facilitates reaction kinetics. As a result, the lithium–sulfur battery achieves high areal capacities of 7.0 mAh cm–2 at 0.56 mA cm–2 and 4.0 mAh cm–2 at 1 mA cm–2 after 100 cycles with a sulfur loading of 10.91 mg cm–2 and an E/S ratio of 6.46 μL mg–1.