Publications

A redox flow battery utilizing two, three-electron polyoxometalate redox couples (SiV^V₃W^VI₉O₄₀^7–/SiV^IV₃W^VI₉O₄₀^10- and SiV^IV₃W^VI₉O₄₀^10-/SiV^IV₃W^V₃W^VI₆O₄₀^13-) was investigated for use in stationary storage in either aqueous or non-aqueous conditions. The aqueous battery had coulombic efficiencies greater than 95% with relatively low capacity fading over 100 cycles. Infrared studies showed there was no decomposition of the compound under these conditions. The non-aqueous analog had a higher operating voltage but at the expense of coulombic efficiency. The spontaneous formation of these clusters by self-assembly facilitates recovery of the battery after being subjected to reversed polarity. Polyoxometalates offer a new approach to stationary storage materials because they are capable of undergoing multi-electron reactions and are stable over a wide range of pH values and temperatures.

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A series of redox flow batteries utilizing mixed addenda (vanadium and tungsten), phosphorus-based polyoxometalates (A-α-PV3W 9O40^6-, B-α-PV3W 9O40^6-, and P2V3W 15O62^9-) were prepared and tested. Cyclic voltammetry and bulk electrolysis experiments on the Keggin compounds (A-α-PV3W9O40^6- and B-α-PV3W9O40^6-) established that the vanadium centers of these compounds could be used as the positive electrode (PV^IV3W^VI9O 40^9-/PV^V3W^VI 9O40^6-), and the tungsten centers could be used as the negative electrode (PV^IV3W^VI 9O40^9-/PV^IV3W ^V3W^VI6O40^12-) since these electrochemical processes are separated by about 1 V. The results showed that A-α-PV3W9O40^6- (where A indicates adjacent, corner-sharing vanadium atoms) had coulombic efficiencies (charge in divided by charge out) above 80%, while the coulombic efficiency of B-α-PV3W9O40^6- (where B indicates adjacent edge-sharing vanadium atoms) fluctuated between 50% and 70% during cycling. The electrochemical yield, a measurement of the actual charge or discharge observed in comparison with the theoretical charge, was between 40% and 50% for A-α-PV3W9O40 ^6-, and ³¹P NMR showed small amounts of PV 2W10O40^5- and PVW11O 40^4- formed with cycling. The electrochemical yield for B-α-PV3W9O40^6- decreased from 90% to around 60% due to precipitation of the compound on the electrode, but there were no decomposition products detected in the solution by ³¹P NMR, and infrared data on the electrode suggested that the cluster remained intact. Testing of P2V3W15O62 ^9- (Wells-Dawson structure) suggested higher charge density clusters were not as suitable as the Keggin structures for a redox flow battery due to the poor stability and inaccessibility of the highly reduced materials. © The Royal Society of Chemistry 2013.

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An iron-based ionic liquid, Fe((OHCH2CH2) 2NH)6(CF3SO3)3, is synthesized in a single-step complexation reaction. Infrared and Raman data suggest NH(CH2CH2OH)2 primarily coordinates to Fe(iii) through alcohol groups. The compound has Tg and Td values of -64°C and 260°C, respectively. Cyclic voltammetry reveals quasi-reversible Fe(iii)/Fe(ii) reduction waves. © 2010 The Royal Society of Chemistry.

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Tantalate materials play a vital role in our high technology society: tantalum capacitors are found in virtually every cell phone. Furthermore, electronic characteristics and the incredibly inert nature of tantalates renders them ideal for applications such as biomedical implants, nuclear waste forms, ferroelectrics, piezoelectrics, photocatalysts and optical coatings. The inert and insoluble nature of tantalates is not fundamentally understood; and furthermore poor solubility renders fabrication of novel or optimized tantalates very difficult. We have developed a soft chemical route to water-soluble tantalum oxide clusters that can serve as both precursors for novel tantalate materials and ideal models for experimental and computational approaches to understanding the unusually inert behavior of tantalates. The water soluble cluster, [Ta6O19]8- is small, highly symmetric, and contains the representative oxygen types of a metal oxide surface, and thus ideally mimics a complex tantalate surface in a simplistic form that can be studied unambiguously. Furthermore; in aqueous solution, these highly charged and super-basic clusters orchestrate surprising acid-base behavior that most likely plays an important role in the inertness of related oxide surfaces. Our unique synthetic approach to the [Ta6O19]8- cluster allowed for unprecedented enrichment with isotopic labels (17O), enabling detailed kinetic and mechanistic studies of the behavior of cluster oxygens, as well as their acid-base behavior. This SAND report is a collection of two publications that resulted from these efforts.

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