Investigating the Effects of Thermally Driven Degradation in Solid Oxide Fuel Cells

One of the most promising devices for low-carbon energy conversion is the solid oxide fuel cell (SOFC). Theoretically, SOFCs show great potential; operating at temperatures between 600-1000 °C the SOFC allows fast reaction kinetics and fuel versatility without the need for expensive platinum catalysts. However in practice, SOFCs can suffer from considerable losses in electrochemical performance due to a multitude of complex degradation mechanisms. This thesis aims to expand our understanding of such mechanisms. Techniques for the three-phase segmentation of SOFC anode materials using nano X-ray computed tomography (CT) and 4D X-ray CT are demonstrated using lab-based instruments, previously only possible using specialist synchrotron facilities. Subsequently, a series of degradation studies are conducted across multiple length-scales using a combination of absorption and diffraction X-ray characterisation methods. Firstly a macroscopic X-ray CT investigation is carried out at cell-level inspecting the effect of start-up time on the delamination of the anode from the electrolyte. Secondly, a microscopic X-ray CT study is conducted on the particle-particle interaction within the anode during operational thermal cycling. Finally, a crystallographic investigation is conducted using synchrotron X-ray powder diffraction to understand the thermo-mechanical properties of anode materials. The experiments reported here improve our understanding of the intrinsic link between the mechanical and electrochemical performance of SOFCs and the influence of microstructure. Understanding is gained from the importance of the materials chosen during manufacturing to the effects of the thermal profiles during operation. These findings are expected to influence the future of SOFC technology from fundamental research to commercial application

Tracking the Lifecycle of a 21700 Cell: A 4D Tomography and Digital Disassembly Study

Extending the lifetime of commercial Li-ion cells is among the most important challenges to facilitate the continued electrification of transport as demonstrated by the substantial volume of literature dedicated to identifying degradation mechanisms in batteries. Here, we conduct a long-term study on a cylindrical Li-ion cell, tracking the evolution of the structure of the cell using X-ray computed tomography. By evaluating the internal geometry of the cell over several hundreds of cycles we show a causal relationship between changes in the electrode structure and the capacity fade associated with cell aging. The rapid aging which occurs as cells reach their end-of-life condition is mirrored in a significant acceleration in internal architecture changes. This work also shows the importance of consistent and accurate manufacturing processes with small defects in the jelly-roll being shown to act as nucleation sites for the structural degradation and by extension capacity fade

Ecological Impacts of the 2015/16 El Niño in the Central Equatorial Pacific

The authors thank Cisco Werner (NOAA/NMFS) for proposing this special issue and encouraging our submission. We thank each of the editors, Stephanie Herring, Peter Stott, and Nikos Christidis, for helpful guidance and support throughout the submittal process. We also thank each of the anonymous external reviewers for thoughtful guidance and suggestions to improve the manuscript. REB, TO, RV, AH, and BVA are grateful for support from the NOAA Coral Reef Conservation Program. AC acknowledges support from the National Science Foundation for the following awards: OCE 1537338, OCE 1605365, and OCE 1031971. This is PMEL contribution no. 4698. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. government. The views expressed in the article are not necessarily those of the U.S. government. (NOAA Coral Reef Conservation Program; OCE 1537338 - National Science Foundation; OCE 1605365 - National Science Foundation; OCE 1031971 - National Science Foundation

Bending and looping of long DNA by Polycomb repressive complex 2 revealed by AFM imaging in liquid

Polycomb repressive complex 2 (PRC2) is a histone methyltransferase that methylates histone H3 at Lysine 27. PRC2 is critical for epigenetic gene silencing, cellular differentiation and the formation of facultative heterochromatin. It can also promote or inhibit oncogenesis. Despite this importance, the molecular mechanisms by which PRC2 compacts chromatin are relatively understudied. Here, we visualized the binding of PRC2 to naked DNA in liquid at the single-molecule level using atomic force microscopy. Analysis of the resulting images showed PRC2, consisting of five subunits (EZH2, EED, SUZ12, AEBP2&nbsp;and RBBP4), bound to a 2.5-kb DNA with an apparent dissociation constant (⁠KappD⁠) of 150 &plusmn; 12 nM. PRC2 did not show sequence-specific binding to a region of high GC content (76%) derived from a CpG island embedded in such a long DNA substrate. At higher concentrations, PRC2 compacted DNA by forming DNA loops typically anchored by two or more PRC2 molecules. Additionally, PRC2 binding led to a 3-fold increase in the local bending of DNA&rsquo;s helical backbone without evidence of DNA wrapping around the protein. We suggest that the bending and looping of DNA by PRC2, independent of PRC2&rsquo;s methylation activity, may contribute to heterochromatin formation and therefore epigenetic gene silencing.</p

Fate of liposomes in presence of phospholipase C and D: from atomic to supramolecular lipid arrangement

Understanding the origins of lipid membrane bilayer rearrangement in response to external stimuli is an essential component of cell biology and the bottom-up design of liposomes for biomedical applications. The enzymes phospholipase C and D (PLC and PLD) both cleave the phosphorus–oxygen bonds of phosphate esters in phosphatidylcholine (PC) lipids. The atomic position of this hydrolysis reaction has huge implications for the stability of PC-containing self-assembled structures, such as the cell wall and lipid-based vesicle drug delivery vectors. While PLC converts PC to diacylglycerol (DAG), the interaction of PC with PLD produces phosphatidic acid (PA). Here we present a combination of small-angle scattering data and all-atom molecular dynamics simulations, providing insights into the effects of atomic-scale reorganization on the supramolecular assembly of PC membrane bilayers upon enzyme-mediated incorporation of DAG or PA. We observed that PC liposomes completely disintegrate in the presence of PLC, as conversion of PC to DAG progresses. At lower concentrations, DAG molecules within fluid PC bilayers form hydrogen bonds with backbone carbonyl oxygens in neighboring PC molecules and burrow into the hydrophobic region. This leads initially to membrane thinning followed by a swelling of the lamellar phase with increased DAG. At higher DAG concentrations, localized membrane tension causes a change in lipid phase from lamellar to the hexagonal and micellar cubic phases. Molecular dynamics simulations show that this destabilization is also caused in part by the decreased ability of DAG-containing PC membranes to coordinate sodium ions. Conversely, PLD-treated PC liposomes remain stable up to extremely high conversions to PA. Here, the negatively charged PA headgroup attracts significant amounts of sodium ions from the bulk solution to the membrane surface, leading to a swelling of the coordinated water layer. These findings are a vital step toward a fundamental understanding of the degradation behavior of PC lipid membranes in the presence of these clinically relevant enzymes, and toward the rational design of diagnostic and drug delivery technologies for phospholipase-dysregulation-based diseases

Direct observations of electrochemically induced intergranular cracking in polycrystalline NMC811 particles

Establishing the nature of crack generation, formation, and propagation is paramount to understanding the degradation modes that govern decline in battery performance. Cracking has several possible origins; however, it can be classified in two general cases: mechanically induced, during manufacturing, or electrochemically induced, during operation. Accurate and repeatable tracking of operational cracking to sequentially image the same material as it undergoes cracking is highly challenging; observing these features requires the highest resolutions possible for 3D imaging techniques, necessitating very small sample geometry, while also achieving realistic electrochemical performance. Here, we present a technique in which particle cracking can be completely attributed to electrochemical stimulation via sequential ex situ imaging in a laboratory X-ray nano computed tomography (CT) instrument. This technique preserves the mechanical and electrochemical response of each particle without inducing damage in the particles except for the effects of high voltage. Significant cracking within the core of secondary particles was observed upon the electrochemical delithiation of NMC811, which propagated radially. As X-ray computed tomography allows for imaging of the particle cores, the particles were not required to be modified/milled, guaranteeing any synthesis induced strain in the particles was maintained during the whole technique, resulting in an observation that contrasts crystallographic data, suggesting a significant volume expansion of the secondary particles

Presacral malakoplakia presenting as foot drop: a case report

Background: Malakoplakia is a rare condition characterized by inflammatory masses with specific histological characteristics. These soft tissue masses can mimic tumors and tend to develop in association with chronic or recurrent infections, typically of the urinary tract. A specific defect in innate immunity has been described. In the absence of randomized controlled trials, management is based on an understanding of the biology and on case reports. Case presentation: Here we describe a case of presacral malakoplakia in a British Indian woman in her late 30s, presenting with complex unilateral foot drop. Four years earlier, she had suffered a protracted episode of intrapelvic sepsis following a caesarean delivery. Resection of her presacral soft tissue mass was not possible. She received empiric antibiotics, a cholinergic agonist, and ascorbic acid. She responded well to medical management both when first treated and following a recurrence of symptoms after completing an initial 8 months of therapy. Whole exome sequencing of the patient and her parents was undertaken but no clear causal variant was identified. Conclusions: Malakoplakia is uncommon but the diagnosis should be considered where soft tissue masses develop at the site of chronic or recurrent infections. Obtaining tissue for histological examination is key to making the diagnosis. This case suggests that surgical resection is not always needed to achieve a good clinical and radiological outcome

Probing the Structure-Performance Relationship of Lithium-Ion Battery Cathodes Using Pore-Networks Extracted from Three-Phase Tomograms

Pore-scale simulations of Li-ion battery electrodes were conducted using both pore-network modeling and direct numerical simulation. Ternary tomographic images of NMC811 cathodes were obtained and used to create the pore-scale computational domains. A novel network extraction method was developed to manage the extraction of N-phase networks which was used to extract all three phases of NMC-811 electrode along with their interconnections Pore network results compared favorably with direct numerical simulations (DNS) in terms of effective transport properties of each phase but were obtained in significantly less time. Simulations were then conducted with combined diffusion-reaction to simulate the limiting current behavior. It was found that when considering only ion and electron transport, the electrode structure could support current densities about 300 times higher than experimentally observed values. Additional case studies were conducted to illustrate the necessity of ternary images which allow separate consideration of carbon binder domain and active material. The results showed a 24.4% decrease in current density when the carbon binder was treated as a separate phase compared to lumping the CBD and active material into a single phase. The impact of nanoporosity in the carbon binder phase was also explored and found to enhance the reaction rate by 16.8% compared to solid binder. In addition, the developed technique used 58 times larger domain volume than DNS which opens up the possibility of modelling much larger tomographic data sets, enabling representative areas of typically inhomogeneous battery electrodes to be modelled accurately, and proposes a solution to the conflicting needs of high-resolution imaging and large volumes for image-based modelling. For the first time, three-phase pore network modelling of battery electrodes has been demonstrated and evaluated, opening the path towards a new modelling framework for lithium ion batteries.The described here was financially supported by the University of Engineering and Technology Lahore, Pakistan as well as the Natural Science and Engineering Research Council (NSERC) of Canada and in the UK by the Faraday Institution (EP/R042012/1 and EP/R042063/1). Pablo A. García-Salaberri thanks the support from the STFC Early Career Award (ST/R006873/1) during his stay at the Electrochemical Innovation La

All-conjugated cationic copolythiophene "rod-rod" block copolyelectrolytes: Synthesis, optical properties and solvent-dependent assembly

The optical and thermal properties and solvent-dependent assembly of all-conjugated cationic copolythiophene block copolyelectrolytes are investigated.</p