Owing to their unique structure, polyoxometalates (POMs) are important compounds with both acidic and oxidizing properties that can be used in acid-catalyzed and redox-catalyzed reactions, as well as in medicinal chemistry and as functional materials . Vanadium-based polyoxometalate materials are an important class of POMs, in which Na 6 V 10 O 28 is a common vanadium-based polyoxometalate produced by condensation and dehydration in acidic vanadium-containing solutions. However, the properties of the compound were reported extensively, but thermodynamic data and thermal stability were hardly available. In this study, Na 6 V 10 O 28 material was synthesized by the liquid phase method and characterized by XRD , thermogravimetry , electron microscopy , and infrared analysis. The results show that the prepared material is Na 6 V 10 O 28 ·18H 2 O and its decomposition product was Na 5 V 12 O 32 . The thermodynamic data of Na 6 V 10 O 28 . nH 2 O and Na 5 V 12 O 32 such as heat capacity, entropy, and enthalpy were calculated by the NKR combined with drop calorimetry . Finally, the obtained data were applied to equilibrium thermodynamic calculations for reactions related to Na 6 V 10 O 28 , including condensation reactions, ammonium salt precipitation, thermal decomposition reactions , and hydrolysis precipitation. The results can be used for theoretical calculations of thermodynamic reactions related to Na 6 V 10 O 28 and Na 5 V 12 O 32 .
Tao Zhou,Lingling Xie,Qing Han,Xinli Yang,Limin Zhu,Xiaoyu Cao
For cost and safety reasons, aqueous batteries are suitable for large-scale energy storage. Among all aqueous batteries, rechargeable aqueous zinc-ion batteries (ZIBs) are promising choices owing to the low equilibrium potential and high volumetric capacity of zinc. However, its development is also severely hindered by the limited available cathode materials, which generally display poor cycling capabilities. As one of the most investigated POVs (polyvanadates) today, (V 10 O 28 ) 6− has been demonstrated to be feasible in energy storage rely on the well-defined structure and fascinating material activity. Herein, we propose a polyvanadate-Na 6 V 10 O 28 with (V 10 O 28 ) 6− anion as a support structure and serve it for the first time as an aqueous ZIBs cathode. The high stability of the (V 10 O 28 ) 6− cluster permits the material to tolerate the reversible (de)insertion of Zn 2+ . As a result, the Na 6 V 10 O 28 cathode delivers a high capacity of 279.5 mAh g −1 after activation and an extraordinary lifespan over 2000 cycles. Furthermore, the pseudocapacitance analysis and GITT test reveal the pseudocapacitance behavior and high Zn 2+ diffusion coefficient (10 −10 cm 2 s −1 ) of the Na 6 V 10 O 28 /Zn cell, respectively. Not only that, ex-situ XRD, XPS, and TEM are also employed to analyze the storage mechanism of Zn 2+ , indicating the synergistic zinc-storage capacity of Na 6 V 10 O 28 and irreversible products. Overall, this work presents new insights into the application of Na 6 V 10 O 28 in aqueous ZIBs and also demonstrates the competitive potential of POVs for energy storage.
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