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Understanding water dynamics in operating fuel cells by operando neutron tomography investigation of different flow field designs
Get PDFWater management plays a key role in ensuring optimum polymer electrolyte fuel cell PEFC performance, and flow field design can influence the ability of a cell to balance maintaining hydration, whilst avoiding flooding and cell failure. This work deepens the understanding of water evolution in different PEFC flow channel designs, namely single serpentine SS , double serpentine DS and parallel, using our novel high speed neutron computed tomography method. We developed our previously reported method by introducing continuous cell rotation, enabling 18 s per tomogram during 1 h holds at 300, 400 and 500 mA cm amp; 8722;2. The volume of water evolved in the cathode, membrane electrode assembly and anode was quantified, and key mechanisms for water droplet formation in the different flow channel designs were elucidated. The parallel flow field design had the poorest water management, with 47 of the cathode flow channel becoming filled after 1 h at 400 mA cm amp; 8722;2. This significant flooding blocked reactant sites and contributed to unstable cell performance and, ultimately, cell failure at higher current densities. The SS cell displayed the best water management, with only 11 of the cathode channel filled with water after 1 h at 500 mA cm amp; 8722;2, compared with 28 of the DS cathode channel. 3D visualisation and analysis of droplet behaviour elucidated how water slugs in the SS were removed in the gas stream, whereas three of the four parallel cathode flow channels became entirely filled with water plugs, blocking gas flow and exacerbating cell flooding. The new insights gained here are expected to extend to novel flow field designs and image based models, with the use of operando neutron CT demonstrated as a powerful technique for both visualising and quantifying water management in operating PEFCs, as well as deepening the knowledge of droplet behaviour in different flow field type
Elektronendynamiksimulation mit Wellenfunktionen für Materialanwendungen Trendbericht Theoretische Chemie 2024 1 3
Get PDFZeitabhängige Simulationen der Elektronendynamik gewinnen für optische Materialien und lichtinduzierte Photoreaktionen an Gewicht. Verständliche visuelle Ergebnisdarstellungen und moderne effiziente Rechenverfahren helfen dabei, die Technik zu verbreiten. Renaissance der Semiempirik In jüngerer Zeit tragen semiempirische Methoden wieder vermehrt dazu bei, die Vorhersagekraft quantenchemischer Simulationen zu steigern. Dichtefunktionaltheorie Auf der Suche nach einem universellen Austauschkorrelationsfunktional sind mathematisch flexible Ansätze für Hybridfunktionale besonders vielversprechend, etwa lokale Hybridfunktionale oder Hybridfunktionale mit lokaler Reichweitenseparierun
Silver Thiophosphate Ag3PS4 as a Multielectron Reaction Active Material for Lithium Solid State Batteries
Get PDFBeyond its Li ion conductivity, the solid electrolyte lithium thiophosphate amp; 946; Li3PS4 exhibits redox activity when its electrochemical stability window is exceeded. As this redox activity can be partially reversible, thiophosphates may be used as cathode active materials CAM . Silver thiophosphate Ag3PS4 is a well known Ag ion conductor, which has the same crystal structure and similar chemical composition as amp; 946; Li3PS4. Here, Ag3PS4 is selected and studied as the CAM for Li solid state batteries Li SSBs with the configuration In InLi amp; 946; Li3PS4 Ag3PS4 amp; 946; Li3PS4 C65 40 50 10 wt . The cells provide a discharge capacity of 325 mAh g 1 at 10 mA g 1, but suffer from continuous capacity fading during cycling with an average Coulomb efficiency of 97 at 50mA g 1. The reaction mechanism is studied using X ray diffraction, X ray photoelectron spectroscopy, Raman spectroscopy, and impedance spectroscopy. Overall, the reaction of Li with Ag3PS4 is found to be initially partially reversible, but over cycling Ag2S and S8 become the activematerials along with the formation of other byproducts such as Ag2P2S6 and Li2P2S
Analysis of Macromolecular Systems as Enabler for Energy and Life Science Applications
Get PDFIdeas concerning the conceptual existence of macromolecular and colloidal systems found their inception at the beginning of the last century. The experimental technology developed to discover and characterize those systems can be associated with seminal pioneers laying the foundations for microscopic, hydrodynamic, and light scattering approaches. In this perspective, we focus our attention on the origins of the discovery and characterization of macromolecular and colloidal systems with selected examples from the beginnings to the present. This perspective attempts to directly interconnect the design of new macromolecular as well as colloidal systems and the simultaneous development of using advanced characterization techniques for design verification. While not claiming a complete coverage of the entire field of modern polymer science, our selected examples concern the field of life science and the recently and rapidly developing area of energy materials. Macromolecular and colloidal systems represent a complex and extensive field of research. This perspective gives a brief historical overview of the major historical achievements in the experimental assessment of such systems. Based on this line of enabled discoveries, the authors perspective on the enabling role of analysis in energy and life science is described with example
Ubiquitin derived artificial binding proteins targeting oncofetal fibronectin reveal scaffold plasticity by beta strand slippage
No full textAffilin proteins, artificial binding proteins based on the ubiquitin scaffold, have been generated by directed protein evolution to yield de novo variants that bind the extra domain B EDB of oncofetal fibronectin, an established marker of tumor neovasculature. The crystal structures of two EDB specific Affilin variants reveal a striking structural plasticity of the ubiquitin scaffold, characterised by amp; 946; strand slippage, leading to different negative register shifts of the amp; 946;5 strands. This process recruits amino acid residues from amp; 946;5 towards the N terminus to an adjacent loop region and subsequent residues into amp; 946;5, respectively, remodeling the binding interface and leading to target specificity and affinity. Protein backbone alterations resulting from amp; 946; strand register shifts, as seen in the ubiquitin fold, can pose additional challenges to protein engineering as structural evidence of these events is still limited and they are difficult to predict. However, they can surface under the selection pressure of directed evolution and suggest that backbone plasticity allowing amp; 946; strand slippages can increase structural diversity, enhancing the evolutionary potential of a protein scaffol
Leveraging large language models for predictive chemistry
Get PDFMachine learning has transformed many fields and has recently found applications in chemistry and materials science. The small datasets commonly found in chemistry sparked the development of sophisticated machine learning approaches that incorporate chemical knowledge for each application and, therefore, require specialized expertise to develop. Here we show that GPT 3, a large language model trained on vast amounts of text extracted from the Internet, can easily be adapted to solve various tasks in chemistry and materials science by fine tuning it to answer chemical questions in natural language with the correct answer. We compared this approach with dedicated machine learning models for many applications spanning the properties of molecules and materials to the yield of chemical reactions. Surprisingly, our fine tuned version of GPT 3 can perform comparably to or even outperform conventional machine learning techniques, in particular in the low data limit. In addition, we can perform inverse design by simply inverting the questions. The ease of use and high performance, especially for small datasets, can impact the fundamental approach to using machine learning in the chemical and material sciences. In addition to a literature search, querying a pre trained large language model might become a routine way to bootstrap a project by leveraging the collective knowledge encoded in these foundation models, or to provide a baseline for predictive task
Interface Engineered Atomic Layer Deposition of 3D Li4Ti5O12 for High Capacity Lithium Ion 3D Thin Film Batteries
Get PDFUpcoming energy autonomous mm scale Internet of things devices require high energy and high power microbatteries. On chip 3D thin amp; 64257;lm batteries TFBs are the most promising option but lack high rate anode materials. Here, Li 4 Ti 5 O12 thin amp; 64257;lms fabricated by atomic layer deposition ALD are electrochemically evaluated on 3D substrates for the amp; 64257;rst time. The 3D Li 4 Ti 5 O12 reveals an excellent footprint capacity of 20.23 amp; 956;Ah cm amp; 8722;2 at 1 C. The outstanding high rate capability is demonstrated with 7.75 amp; 956;Ah cm amp; 8722;2 at 5 mA cm amp; 8722;2 250 C while preserving a remarkable capacity retention of 97.4 after 500 cycles. Planar amp; 64257;lms with various thicknesses exhibit electrochemical nanoscale e amp; 64256;ects and are tuned to maximize performance. The developed ALD process enables conformal high quality spinel 111 textured Li 4 Ti 5 O12 amp; 64257;lms on Si substrates with an area enhancement of 9. Interface engineering by employing ultrathin AlOx on the current collector facilitates a required crystallization time reduction which ensures high amp; 64257;lm and interface quality and prospective on chip integration. This work demonstrates that 3D Li4 Ti 5 O12 by ALD can be an attractive solution for the microelectronics compatible fabrication of scalable high energy and high power Li ion 3D TFB
Dynamics of bulk and surface oxide evolution in copper foams for electrochemical CO2 reduction
No full textOxide derived copper OD Cu materials exhibit extraordinary catalytic activities in the electrochemical carbon dioxide reduction reaction CO2RR , which likely relates to non metallic material constituents formed in transitions between the oxidized and the reduced material. In time resolved operando experiment, we track the structural dynamics of copper oxide reduction and its re formation separately in the bulk of the catalyst material and at its surface using X ray absorption spectroscopy and surface enhanced Raman spectroscopy. Surface species transformations progress within seconds whereas the subsurface bulk processes unfold within minutes. Evidence is presented that electroreduction of OD Cu foams results in kinetic trapping of subsurface bulk oxide species, especially for cycling between strongly oxidizing and reducing potentials. Specific reduction oxidation protocols may optimize formation of bulk oxide species and thereby catalytic properties. Together with the Raman detected surface adsorbed OH and C containing species, the oxide species could collectively facilitate CO adsorption, resulting an enhanced selectivity towards valuable C2 products during CO2R
Innovative Insights into Water Oxidation Mechanism Investigating Birnessite s Reaction with Cerium IV Ammonium Nitrate
No full textDeveloping Mn based water oxidation reaction WOR catalysts is key for renewable energy storage, utilizing Mn s abundance, cost effectiveness, and natural role. Cerium IV ammonium nitrate CAN has been widely utilized as a sacrificial oxidant in the exploration of WOR catalysts. In this study, advanced techniques, such as X ray absorption spectroscopy XAS , in situ Raman spectroscopy, and in situ electron paramagnetic resonance EPR , to delve into the WOR facilitated by CAN and birnessite were employed. XANES analysis has demonstrated that the average oxidation states AOSs of Mn in birnessite, a birnessite CAN mixture, and in the birnessite CAN mixture postwater addition are 3.7, 3.8, and 3.9, respectively. In situ Raman spectroscopy performed in the presence of birnessite and CAN revealed a distinct peak at 784 cm 1, which is attributed to Mn IV amp; 9552;O. A shift of this peak to 769 cm 1 in H218O confirms its association with Mn IV amp; 9552;O. No change in this peak was observed in D2O, further supporting the notion that it is linked to Mn IV amp; 9552;O rather than Mn OH D . Furthermore, EPR spectroscopy shows the presence of Mn IV . It is suggested that the WOR mechanism initiates with the oxidation of birnessite by CAN, which enhances the concentration of Mn IV sites in the birnessite structure. Under acidic conditions, birnessite, enriched in Mn IV , facilitates oxygen evolution and subsequently transitions into a form with reduced Mn IV levels. This process highlights the critical function of the Mn hydr oxide structure, similar to its role in the water oxidizing complex of Photosystem II, where it serves as charge storage for oxidizing equivalents from CAN, paving the way for a four electron reaction that drives the WO
Design and Characterization of Functional Self assembled Monolayers in Context of Organic and Molecular Electronics
No full textThis thesis deals with the design and characterization of self assembled monolayers SAMs in the context of organic and molecular electronics. Within the first subproject, I studied the effect of tail group substitution on the charge transport properties of oligophenylenethiolate SAMs on Au 111 . Such a substitution is frequently used for electrostatic interface engineering in organic electronics. Specifically, thiolate SAMs with phenyl, biphenyl, and terphenyl backbone and amp; 8722;H, amp; 8722;CH3, amp; 8722;F, and amp; 8722;CF3 substitutions on Au 111 were studied. These SAMs were found to exhibit dense molecular packing and upright orientation. The introduction of amp; 8722;F and especially amp; 8722;CF3 groups significantly elevates the work function WF of the system. For the SAMs with the same molecular backbone length, the current density amp; 119869; demonstrates pronounced dependence on the identity of the tail group R , with the highest amp; 119869; for R amp; 8722;CH3, followed by R amp; 8722;H, amp; 8722;CF3, and amp; 8722;F, in decreasing order. No correlation of this behavior with the WF was found; it was tentatively attributed to the difference in the projected density of states PDOS in the region of the terminal tail groups, the difference in effective electrical contact area at the SAM Ga2O3 interface, and the appearance of an internal electrostatic field built in field within the SAMs, emerging at their contact to the top Ga2O3 EGaIn electrode .