Gallant B.M.,Massachusetts Institute of Technology |
Kwabi D.G.,Massachusetts Institute of Technology |
Mitchell R.R.,Massachusetts Institute of Technology |
Zhou J.,Canadian Light Source Inc. |
And 2 more authors.
Energy and Environmental Science | Year: 2013
Understanding the origins of high overpotentials required for Li 2O2 oxidation in Li-O2 batteries is critical for developing practical devices with improved round-trip efficiency. While a number of studies have reported different Li2O2 morphologies formed during discharge, the influence of the morphology and structure of Li2O2 on the oxygen evolution reaction (OER) kinetics and pathways is not known. Here, we show that two characteristic Li2O2 morphologies are formed in carbon nanotube (CNT) electrodes in a 1,2-dimethoxyethane (DME) electrolyte: discs/toroids (50-200 nm) at low rates/overpotentials (10 mA gC-1 or E > 2.7 V vs. Li), or small particles (<20 nm) at higher rates/overpotentials. Upon galvanostatic charging, small particles exhibit a sloping profile with low overpotential (<4 V) while discs exhibit a two-stage process involving an initially sloping region followed by a voltage plateau. Potentiostatic intermittent titration technique (PITT) measurements reveal that charging in the sloping region corresponds to solid solution-like delithiation, whereas the voltage plateau (E = 3.4 V vs. Li) corresponds to two-phase oxidation. The marked differences in charging profiles are attributed to differences in surface structure, as supported by X-ray absorption near edge structure (XANES) data showing that oxygen anions on disc surfaces have LiO2-like electronic features while those on the particle surfaces are more bulk Li 2O2-like with modified electronic structure compared to commercial Li2O2. Such an integrated structural, chemical, and morphological approach to understanding the OER kinetics provides new insights into the desirable discharge product structure for charging at lower overpotentials. © 2013 The Royal Society of Chemistry. Source
Mcbeth J.M.,Canadian Light Source Inc. |
Fleming E.J.,Bigelow Laboratory for Ocean Sciences |
Emerson D.,Bigelow Laboratory for Ocean Sciences
Environmental Microbiology Reports | Year: 2013
Oxygen-dependent, neutrophilic iron-oxidizing bacteria (FeOB) are important drivers of iron transformations in marine and freshwater environments. Despite remarkable similarities in physiology and morphotype, known freshwater and marine FeOB are clustered in different classes of Proteobacteria; freshwater FeOB in the Betaproteobacteria and marine FeOB in the Zetaproteobacteria. To determine effects of salinity on these microbes, we examined the mineral biosignatures and molecular ecology of bacteria in FeOB mats collected along an estuarine salinity gradient. Light microscopy and scanning electron microscopy analyses showed the presence of iron oxide stalk and sheath structures in both freshwater and saline iron mats. Results of tagged pyrosequencing, quantitative PCR and fluorescent in situ hybridization, all based on the small subunit rRNA gene, confirmed Zetaproteobacteria were not present in freshwater mats, but were in saline mats at salinities down to 5‰. Among the Betaproteobacteria, Leptothrix spp. were only found in the freshwater mat. Gallionella spp. were limited to freshwater and low salinity mats (<5‰). Sideroxydans sp. were salt tolerant; however, their relative abundance decreased with increasing salinity. These results suggest salinity is important in shaping the population biology of iron mat communities, and some coexistence between marine and freshwater populations occurs in brackish waters. © 2013 John Wiley & Sons Ltd and Society for Applied Microbiology. Source
Cutler J.,Canadian Light Source Inc.
Synchrotron Radiation News | Year: 2014
Since the concept of a synchrotron research facility in Canada in the mid-1990s, utilization by industry has been a pillar that has made the Canadian Light Source (CLS) unique in the global synchrotron community. With few synchrotron facilities working with the private sector in 1995, the relevance of a highly active industrial science program was questioned by many stakeholder groups, but as the CLS proposal was being developed, it became abundantly clear that for a synchrotron to be successful in Canada, it would need the support of both academia and industry; a dedicated industrial science group therefore became an integral part of the CLS. Copyright Taylor & Francis. Source
Bewer B.E.,Canadian Light Source Inc.
Journal of Synchrotron Radiation | Year: 2013
Analyzer-based imaging has improved tissue X-ray imaging beyond what conventional radiography was able to achieve. The extent of the improvement is dependent on the crystal reflection used in the monochromator and analyzer combination, the imaging photon energy, the geometry of the sample and the imaging detector. These many factors determine the ability of the system to distinguish between various bone tissues or soft tissues with a specified statistical certainty between pixels in a counting detector before any image processing. The following discussion will detail changes in the required number of imaging photons and the resulting surface absorbed dose when the imaging variables are altered. The process whereby the optimal imaging parameters to deliver the minimum surface absorbed dose to a sample while obtaining a desired statistical certainty between sample materials for an arbitrary analyzer-based imaging system will be described. Two-component samples consisting of bone and soft tissue are discussed as an imaging test case. The two-component approach will then be generalized for a multiple-component sample. © 2013 International Union of Crystallography Printed in Singapore-all rights reserved. Source
Martynowski D.,University of Saskatchewan |
Grochulski P.,Canadian Light Source Inc. |
Howard P.S.,University of Saskatchewan
Acta Crystallographica Section D: Biological Crystallography | Year: 2013
Vibrio vulnificus utilizes the type II secretion system (T2SS), culminating in a megadalton outer membrane complex called the secretin, to translocate extracellular proteins from the periplasmic space across the outer membrane. In Aeromonas hydrophila, the general secretion pathway proteins ExeA and ExeB form an inner membrane complex which interacts with peptidoglycan and is required for the assembly of the secretin composed of ExeD. In V. vulnificus, these two proteins are fused into one protein, EpsAB. Here, the crystal structure of a periplasmic domain of EpsAB (amino acids 333-584) solved by SAD phasing is presented. The crystals belonged to space group C2 and diffracted to 1.55Å resolution. Source