Redox cycling of solid oxide fuel cells

Imperial Users onl

Three-Phase Segmentation of Solid Oxide Fuel Cell Anode Materials Using Lab Based X-ray Nano-Computed Tomography

Triple-phase boundaries are an important microstructural metric to assess the performance and durability of solid oxide fuel cell electrodes and are known to significantly influence the performance at cell level. In recent years many advancements have been made in the quantification of TPBs including the use of focused ion beam scanning electron microscopes and synchrotron X-ray tomography, although neither technique comes without limitation; the former being destructive and the latter having limited availability. This work demonstrates the first example of the application of lab-based X-ray nano-CT for non-destructive, microstructural characterization of a SOFC electrode, where three-phase segmentation has been achieved. A SOFC anode cermet consisting of nickel and yttria-stabilized zirconia was imaged under X-ray using two fields of view: 64 µm × 64 µm and 16 µm × 16 µm, with compositional data displayed for several samples at the two resolutions. This work highlights the possibility of three-phase segmentation using lab-based equipment allowing non-destructive quantification and mapping of triple-phase boundaries without the need for synchrotron radiation

The contributions to long-term health-relevant particulate matter at the UK EMEP supersites between 2010 and 2013: Quantifying the mitigation challenge

Human health burdens associated with long-term exposure to particulate matter (PM) are substantial. The metrics currently recommended by the World Health Organization for quantification of long-term health-relevant PM are the annual average PM10 and PM2.5 mass concentrations, with no low concentration threshold. However, within an annual average, there is substantial variation in the composition of PM associated with different sources. To inform effective mitigation strategies, therefore, it is necessary to quantify the conditions that contribute to annual average PM10 and PM2.5 (rather than just short-term episodic concentrations). PM10, PM2.5, and speciated water-soluble inorganic, carbonaceous, heavy metal and polycyclic aromatic hydrocarbon components are concurrently measured at the two UK European Monitoring and Evaluation Programme (EMEP) ‘supersites’ at Harwell (SE England) and Auchencorth Moss (SE Scotland). In this work, statistical analyses of these measurements are integrated with air-mass back trajectory data to characterise the ‘chemical climate’ associated with the long-term health-relevant PM metrics at these sites. Specifically, the contributions from different PM concentrations, months, components and geographic regions are detailed. The analyses at these sites provide policy-relevant conclusions on mitigation of (i) long-term health-relevant PM in the spatial domain for which these sites are representative, and (ii) the contribution of regional background PM to long-term health-relevant PM. At Harwell the mean (±1 sd) 2010–2013 annual average concentrations were PM10 = 16.4 ± 1.4 μg m−3 and PM2.5 = 11.9 ± 1.1 μg m−3 and at Auchencorth PM10 = 7.4 ± 0.4 μg m−3 and PM2.5 = 4.1 ± 0.2 μg m−3. The chemical climate state at each site showed that frequent, moderate hourly PM10 and PM2.5 concentrations (defined as approximately 5–15 μg m−3 for PM10 and PM2.5 at Harwell and 5–10 μg m−3 for PM10 at Auchencorth) determined the magnitude of annual average PM10 and PM2.5 to a greater extent than the relatively infrequent high, episodic PM10 and PM2.5 concentrations. These moderate PM10 and PM2.5 concentrations were derived across the range of chemical components, seasons and air-mass pathways, in contrast to the highest PM concentrations which tended to associate with specific conditions. For example, the largest contribution to moderate PM10 and PM2.5 concentrations – the secondary inorganic aerosol components, specifically NO3− – were accumulated during the arrival of trajectories traversing the spectrum of marine, UK, and continental Europe areas. Mitigation of the long-term health-relevant PM impact in the regions characterised by these two sites requires multilateral action, across species (and hence source sectors), both nationally and internationally; there is no dominant determinant of the long-term PM metrics to target

Tailoring SOFC electrode microstructures for improved performance

The authors thank EPSRC for support through the research grant EP/M014304/1.The key technical challenges that fuel cell developers need to address are performance, durability, and cost. All three need to be achieved in parallel; however, there are often competitive tensions, e.g., performance is achieved at the expense of durability. Stability and resistance to degradation under prolonged operation are key parameters. There is considerable interest in developing new cathodes that are better able to function at lower temperature to facilitate low cost manufacture. For anodes, the ability of the solid oxide fuel cell (SOFC) to better utilize commonly available fuels at high efficiency, avoid coking and sulfur poisoning or resistance to oxidation at high utilization are all key. Optimizing a new electrode material requires considerable process development. The use of solution techniques to impregnate an already optimized electrode skeleton, offers a fast and efficient way to evaluate new electrode materials. It can also offer low cost routes to manufacture novel structures and to fine tune already known structures. Here impregnation methodologies are discussed, spectral and surface characterization are considered, and the recent efforts to optimize both cathode and anode functionalities are reviewed. Finally recent exemplifications are reviewed and future challenges and opportunities for the impregnation approach in SOFCs are explored.PostprintPeer reviewe

Redox cycling of solid oxide fuel cells

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