Selective nitrogen adsorption via backbonding in a metal-organic framework with exposed vanadium sites.

Industrial processes prominently feature π-acidic gases, and an adsorbent capable of selectively interacting with these molecules could enable important chemical separations1-4. Biological systems use accessible, reducing metal centres to bind and activate weakly π-acidic species, such as N2, through backbonding interactions5-7, and incorporating analogous moieties into a porous material should give rise to a similar adsorption mechanism for these gaseous substrates8. Here, we report a metal-organic framework featuring exposed vanadium(II) centres capable of back-donating electron density to weak π acids to successfully target π acidity for separation applications. This adsorption mechanism, together with a high concentration of available adsorption sites, results in record N2 capacities and selectivities for the removal of N2 from mixtures with CH4, while further enabling olefin/paraffin separations at elevated temperatures. Ultimately, incorporating such π-basic metal centres into porous materials offers a handle for capturing and activating key molecular species within next-generation adsorbents

Plasma-enhanced atomic layer deposition of vanadium phosphate as a lithium-ion battery electrode material

Vanadium phosphate films were deposited by a new process consisting of sequential exposures to trimethyl phosphate (TMP) plasma, O2 plasma, and either vanadium oxytriisopropoxide [VTIP, OV(O-i-Pr)3] or tetrakisethylmethylamido vanadium [TEMAV, V(NEtMe)4] as the vanadium precursor. At a substrate temperature of 300 °C, the decomposition behavior of these precursors could not be neglected; while VTIP decomposed and thus yielded a plasma-enhanced chemical vapor deposition process, the author found that the decomposition of the TEMAV precursor was inhibited by the preceding TMP plasma/O2 plasma exposures. The TEMAV process showed linear growth, saturating behavior, and yielded uniform and smooth films; as such, it was regarded as a plasma-enhanced atomic layer deposition process. The resulting films had an elastic recoil detection-measured stoichiometry of V1.1PO4.3 with 3% hydrogen and no detectable carbon contamination. They could be electrochemically lithiated and showed desirable properties as lithium-ion battery electrodes in the potential region between 1.4 and 3.6 V versus Li+/Li, including low capacity fading and an excellent rate capability. In a wider potential region, they showed a emarkably high capacity (equivalent to three lithium ions per vanadium atom), at the expense of reduced cyclability.status: publishe

Developing vanadium redox flow technology on a 9-kW 26-kWh industrial scale test facility: Design review and early experiments

Redox Flow Batteries (RFBs) have a strong potential for future stationary storage, in view of the rapid expansion of renewable energy sources and smart grids. Their development and future success largely depend on the research on new materials, namely electrolytic solutions, membranes and electrodes, which is typically conduced on small single cells. A vast literature on these topics already exists. However, also the technological development plays a fundamental role in view of the successful application of RFBs in large plants. Despite that, very little research is reported in literature on the technology of large RFB systems. This paper presents the design, construction and early operation of a vanadium redox flow battery test facility of industrial size, dubbed IS-VRFB, where such technologies are developed and tested. In early experiments a peak power of 8.9 kW has been achieved with a stack specific power of 77Wkg−1. The maximum tested current density of 635 mA cm−2 has been reached with a cell voltage of 0.5 V, indicating that higher values can be obtained. The test facility is ready to be complemented with advanced diagnostic devices, including multichannel electrochemical impedance spectroscopy for studying aging and discrepancies in the cell behaviors

Metalliferous Biosignatures for Deep Subsurface Microbial Activity

Acknowledgments We thank the British Geological Survey (BGS) for the provision of samples and the Science & Technology Facilities Council (STFC) grant (ST/L001233/1) for PhD funding which aided this project. Research on selenium in reduction spheroids was also supported by NERC grants (NE/L001764/1 and NE/ M010953/1). The University of Aberdeen Raman facility was funded by the BBSRC. We also thank John Still for invaluable technical assistance.Peer reviewedPublisher PD

Visualization of one-dimensional diffusion and spontaneous segregation of hydrogen in single crystals of VO2

Hydrogen intercalation in solids is common, complicated, and very difficult to monitor. In a new approach to the problem, we have studied the profile of hydrogen diffusion in single-crystal nanobeams and plates of VO2, exploiting the fact that hydrogen doping in this material leads to visible darkening near room temperature connected with the metal-insulator transition at 65 {\deg}C. We observe hydrogen diffusion along the rutile c-axis but not perpendicular to it, making this a highly one-dimensional diffusion system. We obtain an activated diffusion coefficient, ~0.01 e^(-0.6 eV/k_B T) cm2sec-1, applicable in metallic phase. In addition, we observe dramatic supercooling of the hydrogen-induced metallic phase and spontaneous segregation of the hydrogen into stripes implying that the diffusion process is highly nonlinear, even in the absence of defects. Similar complications may occur in hydrogen motion in other materials but are not revealed by conventional measurement techniques