Events: Fysik events at Chalmers University of TechnologyWed, 18 Jan 2023 14:25:52 +0100éa-Strandberg-230208.aspxéa Strandberg, Physics<p>PJ, seminar room, Fysik Origo, Campus Johanneberg</p><p>​Title: Electrode degradation in polymer electrolyte fuel cells</p>​<div><strong>Abstract</strong>: <span style="background-color:initial">To mitigate the climate crisis, and reduce carbon emissions from e.g. the</span></div> <div>transport and energy sectors, hydrogen has been proposed to be used as an</div> <div>environmentally friendly alternative energy carrier. Proton exchange membrane</div> <div>fuel cells (PEMFCs) use hydrogen as a fuel to create electricity with the only</div> <div>byproducts being water and heat, and are well suited as a power source for e.g.</div> <div>vehicles. However, for successful commercialisation of PEMFCs, some hurdles</div> <div>need to be overcome. In particular, lifetime is a limiting factor for PEMFC</div> <div>due to harsh operational conditions. To improve lifetime, the mechanisms by</div> <div>which the materials in PEMFCs degrade must first be better understood.</div> <div>In this thesis, I present a study on the behaviour of Pt, which is currently</div> <div>the sate-of-the-art catalyst for PEMFC, during electrochemical procedures in</div> <div>liquid electrolytes, studied using electrochemical quartz crystal micro-balance</div> <div>(EQCM). Mass response and dissolution rates for Pt thin films were studied</div> <div>in acid and alkaline environments. The Pt dissolution rate was found to be</div> <div>similar in alkaline and acidic electrolyte when normalised to electrochemical</div> <div>surface area. Furthermore, I present identical location (IL) microscopy implemented in</div> <div>a real 5 cm2 single-cell fuel cell, to follow the degradation of Pt catalyst on</div> <div>carbon support under realistic operation conditions. With both IL scanning</div> <div>electron microscopy (IL-SEM) and IL transmission electron microscopy (ILTEM),</div> <div>I show that the degradation processes can be followed during different</div> <div>types of ageing processes. IL-SEM show that the carbon support material is</div> <div>stable during normal fuel cell operation conditions, while the Pt particles grow.</div> <div>IL-TEM show similar result for the normal condition operation as seen with</div> <div>the IL-SEM. However, during start-up/shutdown conditions, IL-TEM show</div> <div>that the carbon support lose volume, and collapse on weak points, which brings</div> <div>Pt particles together, and promotes Pt particle growth. The developed IL</div> <div>techniques presented in this thesis helps distinguish the degradation effects of</div> <div>different operation conditions and opens up for further testing of degradation</div> <div>processes under real fuel cell conditions.</div> Fazi, Materials Science<p>PJ, seminar room, Fysik Origo, Campus Johanneberg</p><p>​Title: Development and performance evaluation of accident-tolerant coated fuel claddings for light water reactors</p>​<div><strong>Abstract</strong>: <span style="background-color:initial">The development of accident tolerant fuel has the aim of providing nuclear fuels able to endure severe accident conditions. Research in this field has also sparked a wave of material renewal in the nuclear industry that had been delayed for the last few decades. Climate change is an ever-growing public concern, and policies about greenhouse gas emissions are becoming more stringent both at the national and international level. Nuclear energy produces very low carbon emissions and the successful development of new accident tolerant materials might play a role in making this technology a viable solution to this global issue. Coated zirconium claddings are one of the most promising candidates as a near-term response to the need for accident tolerant materials. These coatings can be produced via a range of different technologies, but two main techniques are being currently employed for the development of such coatings: cold spray deposition and physical vapour deposition (PVD). In cold spray, high pressure gas is fed through a nozzle together with a powder. Powder particles are accelerated up to 1200 m/s and directed to the substrate, in this case cladding tubes made of zirconium alloy. In PVD, the coating material is evaporated from a target and sputtered onto the substrate as atoms or ions. The resulting coated zirconium claddings are the subject of this work.</span></div> <div><br /></div> <div>As-fabricated samples, autoclave tested material, and specimens tested under simulated accident conditions are characterized with atom probe tomography and a range of electron microscopy techniques. The scope of the investigation is to evaluate the performance of the coated claddings under operating conditions and in simulated accident conditions. Metallic Cr has emerged as the best candidate for accident tolerant coatings for pressurised water reactors. In this work, the focus was on Cr-coatings deposited with cold spray, which performed well in both tested environments. A passivating layer of chromia formed during autoclave exposure, and a protective scale of chromia prevented any oxidation of the Zrsubstrate for up to 40 min in 1200  C steam. The nature of the adhesion in cold spray coatings and the effects of this deposition method on the substrate were studied. The formation of a Cr2Zr phase at the Cr/Zr interface was observed both under autoclave and simulated accident conditions. The search for an effective accident tolerant coating for boiling water reactors is more challenging and many coatings have been tested in autoclave, where PVD (Cr,Nb)N coatings showed the best performance under operating conditions. A 200 nm thick passivating oxide film composed of an outer Cr, Nb, Ni phase and an inner layer of oxidised coating was found after exposure.</div> <div><br /></div> Revealing the nanoworld of trees<p>Kollektorn, lecture room, MC2-huset, Campus Johanneberg</p><p>​​​​​​Welcome to a seminar in the series SmallTalks [about Nanoscience] arranged by the Excellence Initiative Nano​. Speaker: Maria Brollo, Postdoc at the Department of Physics, Nano and Biophysics.  Coffee will be served before the start of the seminar.</p><strong>Title</strong>: Revealing the nanoworld of trees<div><strong>Abstract</strong>: <span style="background-color:initial">Wood is the most abundant biopolymer on Earth. Sweden is the world’s second largest exporter of paper, pulp and sawn wood products, giving the Swedish industries an important international position. Sweden is developing sustainable bio-based alternatives to today’s fossil-based materials since wood is renewable. One of the research projects into new technologies focused on wood is biofuel. By treating the wood with different processes, one can enhance its porosity, increasing its surface to area ratio. Increasing the porosity also means the increase of enzyme accessibility to the cellulosic component. Enzymes are important in wood decomposition because they act precisely on specific chemical bonds in the plant cell wall. These enzymes convert polysaccharides into fermentable sugars. Given the nanometric size of enzymes, around 4 nm, electron microscopy offers a unique capability for site specific imaging with high spatial resolution, which is the focus of this talk. </span></div> <div>Different electron microscopy techniques can be used to investigate wood specimens. Scanning electron microscopy (SEM) is used for surface evaluation on the porosity level after different wood treatments. Focused ion beam (FIB) combined with SEM reveal the internal microstructure of wood by cross-sections cuts. While transmission electron microscopy (TEM) addresses the nanostructure of wood composites besides the evaluation of enzymes.</div> <div><br /></div> [about Nanoscience] with Jakub Fojt<p>Kollektorn, lecture room, MC2-huset, Campus Johanneberg</p><p>​​​​​​Welcome to a seminar in the series SmallTalks [about Nanoscience] arranged by the Excellence Initiative Nano​. Speaker: Jakub Fojt, PhD student at Condensed Matter and Materials Theory, Department of Physics.  Coffee will be served before the start of the seminar.</p>​Abstract: TBA for Tomorrow 2023<p>RunAn, conference hall, Kårhuset, Campus Johanneberg</p><p>​​SAVE THE DATE: The topic of the 2023 Materials for Tomorrow is &quot;Surface of Things&quot;, and the event will take place at Chalmers Conference Centre on Nov 9-10 with several internationally recognised speakers.  A preliminary program will be presented in July.​</p>