Huge Electron Sponge of Polyoxometalate toward Advanced Lithium-Ion Storage.

The huge polyoxometalate, Na48[HxMo256VIMo112VO1032(H2O)240(SO4)48] ({Mo368}), which can be prepared by a facile solution process and can be applied in lithium-ion storage applications as the anode. The large and open hollow nanostructure is promising to store a larger number of lithium ions and expedite the diffusion of lithium ions. A single {Mo368} nanocluster can transfer 624 electrons, referred to as a "huge electron sponge". Pure {Mo368} without any support materials exhibits very high capacities of 964 mA h g-1 with hardly any decay for 100 cycles at 0.1 A g-1 and still maintains 761 mA h g-1 after 180 cycles at 0.5 A g-1, indicating great cycling stability. The {Mo368} anode provides excellent rate performance and reversibility during the lithiation/delithiation processes, which are contributed by both the diffusion-controlled process and the capacitive process. The capacitive contribution can reach 71.7% at a scan rate of 2 mV s-1. The high DLi+ value measured by GITT confirms the fast reaction kinetics of the {Mo368} electrode. The {Mo368}//NCM111-A full cell is practically applied to light LED lamps. These investigations indicate that {Mo368} nanoclusters are advanced energy storage materials with high capacities, fast charge transfer, and low-cost mass production for lithium-ion storage. Moreover, {Mo368} should be considered a clean energy material because there is no production of environmental pollution during the charge/discharge processes.

Photoluminescent honeycomb films templated by microwater droplets.

The europium polyoxometalate anion, [EuW(10)O(36)](9-), can be transferred from an aqueous phase into a chloroform phase through encapsulation by dioctadecyldimethylammonium (DODMA(+)). The formed (DODMA)(9)[EuW(10)O(36)] complexes can self-assemble into ordered, uniform porous honeycomb films by using a simple solvent-evaporation method at the air/water interface without any extra moist airflow. TEM, SEM, and AFM observations show porous morphologies with pores having a diameter of about 2 microm and a wall depth of about 0.8 microm. The microlamellar structure and crystalline nanoaggregates of (DODMA)(9)[EuW(10)O(36)] complexes in films are characterized by XRD measurements and high-resolution TEM observations. During self-assembly into porous honeycomb films, it is speculated that the cooled microwater droplets that are induced by the quick evaporation of chloroform act as the templates for pores and that (DODMA)(9)[EuW(10)O(36)] complexes are deposited around pores. Because of the intrinsic fluorescence of [EuW(10)O(36)], the photoluminescent porous honeycomb films of (DODMA)(9)[EuW(10)O(36)] complexes can emit fluorescence when they are excited by UV light. It is expected that this will meet more requirements of new materials for fluorescence, separation membranes, microstructured electrode surfaces, containers, and reactors.

Macroporous honeycomb films of surfactant-encapsulated polyoxometalates at air/water interface and their electrochemical properties.

A series of surfactant-encapsulated polyoxometalates which have different compositions, shapes, and sizes, are able to self-assemble to the highly ordered honeycomb-structured macroporous films at the air/water interface without any extra moist airflow across the solution surface. The honeycomb film pores in the average diameter of 2-3 µm are obtained, which are independent of the polyoxometalates. It is speculated that the cooled micrometer water droplets act as the necessary templates for the formation of macropores, and the stability of these water droplets is crucial during the self-assembly. With increasing the concentration of surfactants, various morphologies from lowly ordered honeycomb films to highly ordered honeycomb films and then to disordered fragments can be modulated. The interfacial tension between chloroform solution and water droplets induces the changes of films. High-resolution TEM observations indicate a close-packed lamellar structure in the ordered honeycomb film walls. The self-assembly successfully performs the transfer of functional polyoxometalates from bulk solutions to interfacial films. Consequently, the produced honeycomb films present electronic activities, such as ferromagnetism and electrochemical properties. These detailed researches will enrich the studies based on materials obtained by encapsulations in cationic surfactants to construct newly nanostructures of polyoxometalates at interfaces, and promote the potential applications of the honeycomb films of surfactant-encapsulated polyoxometalates in advanced materials.

Formation mechanism and morphology modulation of honeycomb hybrid films made of polyoxometalates/surfactants at the air/water interface.

Highly ordered honeycomb hybrid films of nanometer-scale polyoxometalates and surfactants were fabricated by a simple solvent-evaporation method at the air/water interface. A good template by micrometer water droplets which are condensed from water vapor because of the quick evaporation of organic solvents plays an important role in the self-patterning of honeycomb films. The morphologies of the thin films can be modulated by the solvent volatility which can not only influence the pore size of the film but also determine whether or not a regular porous structure can be achieved at all. The faster the volatility of organic solvents, the smaller the pores of films. Higher hydrophobicity and larger surface coverage which are induced by the surface encapsulation of a polyoxometalate by cationic surfactants with longer double carbon chains are beneficial to the organization of porous structures. It is also found that the morphologies of the thin films can be changed when the thin films are dropped at different supporting solution interfaces. It is well demonstrated that the morphologies of the fabricated hybrid films are modulated by appropriate controls.