Feng-Cui Shen

Polyoxomolybdate–Polypyrrole/Reduced Graphene Oxide Nanocomposite as High-Capacity Electrodes for Lithium Storage

A nanocomposite polyoxomolybdate (PMo12)–polypyrrole (PPy)/reduced graphene oxide (RGO) is fabricated by using a simple one-pot hydrothermal method as an electrode material for lithium-ion batteries. This facile strategy skillfully ensures that individual polyoxometalate (POM) molecules are uniformly immobilized on the RGO surfaces because of the wrapping of polypyrrole (PPy), which avoids the desorption and dissolution of POMs during cycling. The unique architecture endows the PMo12–PPy/RGO with the lithium storage behavior of a hybrid battery–supercapacitor electrode: the nanocomposite with a lithium storage capacity delivers up to 1000 mAh g–1 at 100 mA g–1 after 50 cycles. Moreover, it still demonstrates an outstanding rate capability and a long cycle life (372.4 mAh g–1 at 2 A g–1 after 400 cycles). The reversible capacity of this nanocomposite has surpassed most pristine POMs and POMs-based electrode materials reported to date.

Self-assembly of polyoxometalate/reduced graphene oxide composites induced by ionic liquids as a high-rate cathode for batteries: “killing two birds with one stone”

The relatively low capacity and poor rate performance of cathodes restrict the development of rechargeable batteries and must be settled urgently due to the ever-growing need of energy storage. Here, we report a new cathode system that produces polyoxometalates (POMs)/ionic liquid (IL)/reduced graphene oxide (RGO) composites, denoted as PIG, by a self-assembly method in which IL plays the role of “killing two birds with one stone”. IL not only facilitates the formation of heterogeneous nanocrystalline composites but also acts as the template reagent to feature the morphology of homogeneous nanobelts on the RGO. The PIG system provides us with a theoretical model at the molecular level to give a detailed comparison of a three-dimensional open skeleton formed by different transition metal linkers and a vanadium cage, on the performance of the cathode in batteries. Finally, the targeted composite Mn3V19-HIL/RGO-1 shows good cycling stability and the best ultrafast rate capabilities (121 mA h g−1 at 5000 mA g−1 and 73 mA h g−1 at 2000 mA g−1 for lithium and sodium ion batteries) of POMs-based composites. Furthermore, the PIG system provides a platform for the design of POMs, and even anionic clusters-based composites in the energy conversion and storage, thus giving access to their versatile architectural design and applications.

Oriented electron transmission in polyoxometalate-metalloporphyrin organic framework for highly selective electroreduction of CO 2

The design of highly stable, selective and efficient electrocatalysts for CO2 reduction reaction is desirable while largely unmet. In this work, a series of precisely designed polyoxometalate-metalloporphyrin organic frameworks are developed. Noted that the integration of {ε-PMo8VMo4VIO40Zn4} cluster and metalloporphyrin endows these polyoxometalate-metalloporphyrin organic frameworks greatly advantages in terms of electron collecting and donating, electron migration and electrocatalytic active component in the CO2 reduction reaction. Thus-obtained catalysts finally present excellent performances and the mechanisms of catalysis processes are discussed and revealed by density functional theory calculations. Most importantly, Co-PMOF exhibits remarkable faradaic efficiency ( > 94%) over a wide potential range (−0.8 to −1.0 V). Its best faradaic efficiency can reach up to 99% (highest in reported metal-organic frameworks) and it exhibits a high turnover frequency of 1656 h−1 and excellent catalysis stability ( > 36 h).While CO2 reduction provides a way to remove carbon from the atmosphere, it is challenging to design effective, selective materials for this process. Here, authors construct metal-organic frameworks from polyoxometalates and porphryins to direct electron flow and improve CO2 reduction efficiencies.

Polyoxometalate-Based Metal–Organic Frameworks with Conductive Polypyrrole for Supercapacitors

Metal-organic frameworks (MOFs) with high porosity could act as an ideal substitute for supercapacitors, but their poor electrical conductivities limit their electrochemical performances. In order to overcome this problem, conductive polypyrrole (PPy) has been introduced and a novel nanocomposite resulting from polyoxometalate (POM)-based MOFs (NENU-5) and PPy has been reported. It comprises the merits of POMs, MOFs, and PPy. Finally, the highly conductive PPy covering the surfaces of NENU-5 nanocrystallines can effectively improve the electron/ion transfer among NENU-5 nanocrystallines. The optimized NENU-5/PPy nanocomposite (the volume of Py is 0.15 mL) exhibits high specific capacitance (5147 mF·cm-2), larger than that of pristine NENU-5 (432 mF·cm-2). Furthermore, a symmetric supercapacitor device based on a NENU-5/PPy-0.15 nanocomposite possesses an excellent areal capacitance of 1879 mF·cm-2, which is far above other MOF-based supercapacitors.