3 resultados para Biological and Chemical Physics

em Digital Commons - Michigan Tech


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Polymer electrolyte fuel cell (PEMFC) is promising source of clean power in many applications ranging from portable electronics to automotive and land-based power generation. However, widespread commercialization of PEMFC is primarily challenged by degradation. The mechanisms of fuel cell degradation are not well understood. Even though the numbers of installed units around the world continue to increase and dominate the pre-markets, the present lifetime requirements for fuel cells cannot be guarantee, creating the need for a more comprehensive knowledge of material’s ageing mechanism. The objective of this project is to conduct experiments on membrane electrode assembly (MEA) components of PEMFC to study structural, mechanical, electrical and chemical changes during ageing and understanding failure/degradation mechanism. The first part of this project was devoted to surface roughness analysis on catalyst layer (CL) and gas diffusion layer (GDL) using surface mapping microscopy. This study was motivated by the need to have a quantitative understanding of the GDL and CL surface morphology at the submicron level to predict interfacial contact resistance. Nanoindentation studies using atomic force microscope (AFM) were introduced to investigate the effect of degradation on mechanical properties of CL. The elastic modulus was decreased by 45 % in end of life (EOL) CL as compare to beginning of life (BOL) CL. In another set of experiment, conductive AFM (cAFM) was used to probe the local electric current in CL. The conductivity drops by 62 % in EOL CL. The future task will include characterization of MEA degradation using Raman and Fourier transform infrared (FTIR) spectroscopy. Raman spectroscopy will help to detect degree of structural disorder in CL during degradation. FTIR will help to study the effect of CO in CL. XRD will be used to determine Pt particle size and its crystallinity. In-situ conductive AFM studies using electrochemical cell on CL to correlate its structure with oxygen reduction reaction (ORR) reactivity

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The copper mining boom in Michigan's Upper Peninsula ended in the mid-1960s, but the historical mining still affects the region to this day. Earlier studies conducted in the Keweenaw have shown that trace metals in the sediments negatively affect benthic macroinvertebrate populations. However, because the concentrations of trace metals that are observed to be toxic often differ significantly between the laboratory and the environment, a better method for determining toxic levels of trace metals in the natural environment is desirable in order to establish surface water quality guidelines that effectively protect aquatic life. There were four research objectives for this research project. First, to determine if trace-level concentrations of copper can result in detectable ecological impacts even in the presence of high dissolved organic carbon (DOC). Second, to determine if there is a "safe" concentration of total dissolved copper below which there is little to no ecological impairment. Third, to establish which streams in the Keweenaw Peninsula have been most impacted by elevated levels of total dissolved copper. Fourth, to use this information to evaluate revisions to the water quality criterion for copper that were recently proposed by the Michigan Department of Environmental Quality (MDEQ). In order to collect water quality and macroinvertebrate data, two sampling surveys of approximately 50 streams were completed in the spring and summer of 2012. Our findings demonstrate that negative ecological impacts can be detected even in the presence of high concentrations of DOC. The majority of surveyed streams showed evidence of total dissolved copper concentrations that were elevated above background levels. Our findings suggest that there are detectable negative impacts below the current water quality standard for copper in many Keweenaw streams. The diversity of benthic macroinvertebrates and the number of species present has been reduced as a result of exposure to copper. Additionally, the multimetric approach used by MDEQ is unable to detect copper impairment in local streams due to the use of several insensitive metrics. The proposed changes to the copper criterion would increase the amount of total dissolved copper allowable despite the fact that approximately 25% of streams sampled have aquatic chemistries that would leave them vulnerable to high levels of copper ions.

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Bacteriorhodopsin (bR), an optoelectric protein found in Halobacterium salinarum, has the potential for use in protein hybrid sensing systems. Bacteriorhodopsin has no intrinsic sensing properties, however molecular and chemical tools permit production of bR protein hybrids with transducing and sensing properties. As a proof of concept, a maltose binding protein-bacteriorhodopsin ([MBP]-bR) hybrid was developed. It was proposed that the energy associated with target molecule binding, maltose, to the hybrid sensor protein would provide a means to directly modulate the electrical output from the MBP-bR bio-nanosensor platform. The bR protein hybrid is produced by linkage between bR (principal component of purified purple membrane [PM]) and MBP, which was produced by use of a plasmid expression vector system in Escherichia coli and purified utilizing an amylose affinity column. These proteins were chemically linked using 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), which facilitates formation of an amide bond between a primary carboxylic acid and a primary amine. The presence of novel protein hybrids after chemical linkage was analyzed by SDSPAGE. Soluble proteins (MBP-only derivatives and unlinked MBP) were separated from insoluble proteins (PM derivatives and unlinked PM) using size exclusion chromatography. The putatively identified MBP-bR protein hybrid, in addition to unlinked bR, was collected. This sample was normalized for bR concentration to native PM and both were deposited onto indium tin oxide (ITO) coated glass slides by electrophoretic sedimentation. The photoresponse of both samples, activated using 100 Watt tungsten lamp at 10 cm distance, were equal at 175 mV. Testing of deposited PM with 1 mM sucrose or 1 mM maltose showed no change in the photoresponse of the xiv material, however addition of 1 mM maltose to the deposited MBP-bR linked hybrid material elicited a 57% decrease in photoresponse indicating a positive response for targeting of maltose. This chemically linked MBP-bR hybrid protein, with bacteriorhodopsin, as a photoresponsive transducing substrate, shows promise for creation of a universal sensing array by attachment of other pertinent sensing materials, in lieu of the maltose binding protein utilized. This strategy would allow significant reduction in sensor size, while increasing responsiveness and sensitivity at nano and picomolar levels.