On the origin and application of the Bruggeman Correlation for analysing transport phenomena in electrochemical systems

The widely used Bruggeman equations correlate tortuosity factors of porous media with their porosity. Finding diverse application from optics to bubble formation, it received considerable attention in fuel cell and battery research, recently. The ability to estimate tortuous mass transport resistance based on porosity alone is attractive, because direct access to the tortuosity factors is notoriously difficult. The correlation, however, has limitations, which are not widely appreciated owing to the limited accessibility of the original manuscript. We retrace Bruggemans derivation, together with its initial assumptions, and comment on validity and limitations apparent from the original work to offer some guidance on its use.<br/

Tracking the evolution of a single composite particle during redox cycling for application in H-2 production

Composite materials consisting of metal and metal oxide phases are being researched intensively for various energy conversion applications where they are often expected to operate under redox conditions at elevated temperature. Understanding of the dynamics of composite evolution during redox cycling is still very limited, yet critical to maximising performance and increasing durability. Here we track the microstructural evolution of a single composite particle over 200 redox cycles for hydrogen production by chemical looping, using multi-length scale X-ray computed tomography. We show that redox cycling triggers a centrifugal redispersion of the metal phase and a centripetal clustering of porosity, both seemingly driven by the asymmetric nature of oxygen exchange in composites. Initially, the particle develops a large amount of internal porosity which boosts activity, but on the long term this facilitates structural and compositional reorganisation and eventually degradation. These results provide valuable insight into redox-driven microstructural changes and also for the design of new composite materials with enhanced durability

System analysis of biogas fuelled solid oxide fuel cell

Biogas is a widely available resource which offers large potential for providing carbon neutral electricity. Anaerobic digestion processes can be used to produce biogas from a wide selection of biological substances which makes it a readily available and local energy source. This thesis investigates energetic and economic performance of a small scale solid oxide fuel cell system running on biogas. In this analysis, biogas is considered to be produced from the following sources: livestock effluents, energy crops, agricultural waste and organic waste. For adequate system setup, a database containing biogas compositions of anaerobic digesters with a power output < 100 kWel for the above mentioned substrates is established and used, to analyse chemical build-up and design the gas cleaning and reforming unit. The database shows, that average CH4 content throughout all substrates lies in the range of 55 %mol. However, large seasonal and daily variations are observed and are independent of used matter. Main contaminants are made up by H2S which leads to catalyst deactivation in reformer and fuel cell. This makes effective gas cleaning necessary, for which ZnO and activated carbons are the most practical solutions. The energy model of the solid oxide fuel cell plant is designed and analysed using the software Aspen Plus&#174 and is set up in such a way, that different kind of reforming options are compared with each other. For the electrochemical modelling of the solid oxide fuel cell stack, data from literature are used in order to account for polarisation losses under varying operating conditions. In addition, cost functions are directly implemented into the system, allowing investment cost as well as economic profitability calculations. The system analysis shows, that highest electric efficiencies of 50.63 % on higher heating value basis is achieved when steam reforming is applied. This value lays around 15 % points above average electric efficiencies of biogas engines based on lower heating value. Highest total plant efficiency (electric plus thermal) of 74.14 % is reached under partial oxidation reforming as exothermic reforming reactions increase thermal output of the plant. Total overnight costs of steam and partial oxidation reforming amount to 113,937 euros and 95,693 euros, respectively. For economic profitability calculation, net present value and payback period are determined by applying German, Italian and Finnish subsidy laws. Hereby, due to highest feed-in tariffs, Italy provides the most economically friendly environment for biogas fuelled SOFCs with payback periods of 17 years and 7.6 years for steam and partial oxidation reforming, respectively. As a conclusion, it can be stated, that solid oxide fuel cells using biogas as fuel feature higher electric efficiencies compared to gas engines. However, specific investment costs are in the range of 3,828 euros/kWel to 4,557 euros/kWel for partial oxidation reforming and steam reforming, exceeding specific investment costs of biogas engines by 1,000 euro/kWel and 1,700 euro/kWel, respectively. This makes such systems only profitable when applying Italian and German subsidies. Even though auto thermal reforming was analysed, it showed neither thermodynamic nor economic advantages over steam or partial oxidation reforming

X-ray micro-tomography as a diagnostic tool for the electrode degradation in vanadium redox flow batteries

Micro-tomography (CT) can be successfully employed to characterize ex situ the structural changes occurring in graphite felt electrodes during vanadium redox flow battery (VRFB) operation. Coupled high resolution X-ray and electron microscopy in conjunction with XPS are used to elucidate the microstructural and chemical changes to the high voltage RFB carbon electrode. The results reveal the onset of corrosion of the carbon felt structure relatively early in the VRFB life-cycle, extended operation is expected to result in extensive microstructural evolution effects. Keywords: X-ray micro-tomography, Vanadium redox flow battery, Electrode degradatio

Initial Proteome Analysis of Model Microorganism Haemophilus influenzae Strain Rd KW20

The proteome of Haemophilus influenzae strain Rd KW20 was analyzed by liquid chromatography (LC) coupled with ion trap tandem mass spectrometry (MS/MS). This approach does not require a gel electrophoresis step and provides a rapidly developed snapshot of the proteome. In order to gain insight into the central metabolism of H. influenzae, cells were grown microaerobically and anaerobically in a rich medium and soluble and membrane proteins of strain Rd KW20 were proteolyzed with trypsin and directly examined by LC-MS/MS. Several different experimental and computational approaches were utilized to optimize the proteome coverage and to ensure statistically valid protein identification. Approximately 25% of all predicted proteins (open reading frames) of H. influenzae strain Rd KW20 were identified with high confidence, as their component peptides were unambiguously assigned to tandem mass spectra. Approximately 80% of the predicted ribosomal proteins were identified with high confidence, compared to the 33% of the predicted ribosomal proteins detected by previous two-dimensional gel electrophoresis studies. The results obtained in this study are generally consistent with those obtained from computational genome analysis, two-dimensional gel electrophoresis, and whole-genome transposon mutagenesis studies. At least 15 genes originally annotated as conserved hypothetical were found to encode expressed proteins. Two more proteins, previously annotated as predicted coding regions, were detected with high confidence; these proteins also have close homologs in related bacteria. The direct proteomics approach to studying protein expression in vivo reported here is a powerful method that is applicable to proteome analysis of any (micro)organism