Fysik // Physics

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Utforskar och använder fysik för att förstå världen och bidrar med tillämpningar, nya material och innovationer som möter dagens behov och framtidens utmaningar.
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Explores and uses physics to understand the world, and provide applications, new materials and innovations that meet today's needs, and the challenges of the future.
Stimulated by major needs and challenges in society and industry, our ambition is to foster a creative environment for academic research, learning, innovations and utilisation. We provide a competitive advantage by linking top-level international and interdisciplinary academic performance in the areas of material science, nanotechnology, life science engineering and energy research with world-leading industrial R&D&I projects.

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Effect of Fuel Cell Operating Potential Window on Pt/C Catalyst Durability
(2023) Hjern, Astrid; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Wickman, Björn; Männikkö, Marika
The proton exchange membrane fuel cell is a potential key player in reducing green house gas emissions. There is, however, a need for further improvements in Pt on carbon support catalyst (Pt/C) durability and costs. The purpose of this thesis is to improve catalyst durability by investigating what upper potential limit (UPL) voltage clipping should be implemented during load cycling. It is further investi gated how scan rate affects catalyst durability. Based on previous research, possible causes and pathways of Pt degradation are discussed. Three catalysts from different producers with varying support surface area are examined with accelerated stress tests (ASTs) using triangular wave . One AST was performed with a scan rate of 250 mV/s in the potential window of 0.6 to 1.0 V. Four ASTs were performed with a scan rate of 50 mV/s with a set lower potential limit (LPL) of 0.6 and varying UPL between 0.7-1.0 V. The electrochemical surface area (ECSA) is calculated to track catalyst degradation at specific intervals during the ASTs. The degradation of the catalyst increases with a higher scan rate from 23 to 26% for scan rates of 50 mV/s and 250 mV/s, respectively. All three catalysts show a decrease in degradation when the UPL is lowered from 1.0 to 0.8 V. With decreased UPL a thinner oxide layer is formed. The degradation increases for two catalysts at UPL 0.7, possibly due to error sources in the method. The Pt/C catalyst with a support area of 750 m2/g displayed the lowest degradation possibly due to a large inter-particle distance. The primary degradation mechanisms for platinum in the potential window of 0.6 and 1.0 V are commonly described as Pt dissolution and agglomeration. Based on the results, it can be concluded that a decreasing UPL in the region 1.0 to 0.8 V and increasing support area results in lower catalyst degradation. However, the influence of initial ECSA variations, low coating quality, and ink age questions the accuracy of the results. Therefore, it would be beneficial to repeat the current tests with a more controllable method.
Exploring factors for electrode prototyping for PEM fuel cells
(2024) Björklund Larsen, Frederikke; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Wickman, Björn; Mikaeili, Parinaz
As the world push to lower carbon dioxide emissions to limit climate change, the need for new technologies becomes more and more critical. Some emerging technology is hydrogen fuel cells and amongst them are proton exchange membrane fuel cells. With all new technologies there are several factors that need development, and this work takes a closer look at the catalyst layer of the cathode. Setting out to increase the platinum loading in the cathode while at the same time avoiding cracks, several catalyst inks were made with varying dispersion matrices. The matrices explored were a) water with ethanol and 1-propanol (2:2:1 weight ratio), b) water with 1-propanol (2:3 weight ratio), c) water with 2-propanol (2:3 weight ratio), d) water with tert-butanol (2:3 weight ratio), e) water with 1-propanol and tert-butanol (2:1:2 weight ratio), and f) water with 1-propanol and tert-butanol (1:1:3 weight ratio). To get a deeper understanding of the ink’s properties, rheological tests of the inks and visual analysis of produced electrodes were performed. These analyses found improved coating quality and a higher viscosity for dispersions with a lower dielectric constant and for inks containing solvent with a lower vapour pressure. The improved behaviour was attributed to improved interactions between the ink’s compounds and slower drying of the coatings, leading to less stresses in the electrodes. An improved electrode quality was also observed when the inks were left to mature on a magnetic stirrer for several days. The maturation step resulted in lower viscosity of the inks indicating smaller effective volume fraction of particles and less electrostatic repulsion and steric hinderance between compounds. A final factor in the process that was tested was increasing the relative humidity during the drying process. Here an improved cracking behaviour was observed for the ink containing more water while the opposite was seen in the ink containing more tert-butanol. These findings point towards the need for specific drying processes for each individual ink
Improvement of decal transfer method for preparing fast and reliable CCM assembly
(2024) Hurtig, Adam; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Wickman, Björn; Mikaeili, Parinaz
As sustainable energy solutions have garnered more importance in society and to governmental bodies, a technology getting attention as being part of the solution and a step in the right direction is the proton exchange membrane fuel cell (PEMFC). This comes as the PEMFC uses hydrogen and oxygen to create electricity, with the side-products being heat and water, which means that it is a very clean energy converter. At the heart of the fuel cell is the catalyst coated membrane (CCM), which is where the reactions take place, and it is the component investigated in this thesis. Although there are multiple ways of fabricating CCMs, the method used in this thesis is the decal transfer method. Using this method, parameters such as temperature and pressure were varied to investigate the optimal parameters under different conditions. These conditions included the usage of different membranes, three different cathode loadings and two CCM areas. During this process, several analytical tools were employed, with the intent of finding the most effective quality check method for in-house production of CCMs. This included the usage of an optical microscope, lightboard and high intensity light. The performance of CCMs assembled using optimized parameters was also examined by in-situ fuel cell testing. Lastly, an investigation into the most appropriate pressure pad material was performed. The results in this thesis outlines the optimal parameters for each condition and proposes both the most effective quality check method and the most suitable pressure pad material.
Investigation of catalyst structure and dispersion methodology on PEMFC catalytic inks and resulting electrodes
(2023) Ulberstad, Emma; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Wickman, Björn; Ernst, Felix
The demand for green energy increases every year, pushing the development of sus tainable energy sources. Proton exchange membrane fuel cells (PEMFCs) are a promising technology for renewable energy conversion due to their clean emissions and high energy-conversion efficiency. The electrodes are a core part of PEMFCs, containing the catalyst at which the electrochemical reactions occur, where hydro gen and oxygen are converted to water and energy. To enhance cost efficiency, performance and durability of PEMFCs, it is essential to better understand the complex and partly unknown properties of the electrode and optimize the electrode production process. There is a need to better understand the dispersion method of the catalyst ink that makes up the electrode because it is one of the major factors determining the electrode properties. The effect of catalyst ink materials, dispersion technique and parameters on the catalyst ink microstructure were studied using rhe ological measurements and light microscope imaging of the electrodes. Dispersion by ultrasonication at higher vibrational amplitude showed an increase in viscosity and less visible agglomerates on the electrode surface as compared to lower amplitudes. A continuous decrease in apparent agglomerate size and abundance was found with increasing ultrasonic energy input. The results also showed a partly unexpected rhe ological trend where highly dispersed inks exhibit poorer rheological properties, such as low viscosity and elastic modulus for the applied coating method as compared to less dispersed inks. Ultrasonication and bead-milling dispersion method resulted in inks with different rheological properties. The investigation showed that rheology and microscopy are able to only partly capture the complex characteristics of the agglomerated structures and complimenting techniques like e.g. SEM and DLS can help further investigation. With this work, an optimization of the ink dispersion process was achieved and further insight into the dispersion parameters allowed to establish dispersion design rules, e.g. regarding the ultrasonic power and energy input, and to further elucidate the interdependency between ink components and dispersion methodology.
Operando plasmon resonance sensoring applied to sodium-ion batteries
(2022) Ewaldsson, Stefan; Chalmers tekniska högskola / Institutionen för fysik; Johansson, Patrik; Langhammer, Elin; Boulaoued, Athmane; Sundvall, Christian
The sodium-ion storage mechanism in hard carbon was studied by the means of nano-plasmonic resonance spectroscopy. The measurements were made operando, using a gold nano-film deposited onto an optical fiber which was inserted into a battery half cell, cycled at different C-rates. The most favourable sensor type was also investigated. It was found that correlation between the optical signal and voltage signal was possible. The fast cycles in the cycling regime used, led to capacity fade, which can be seen to mainly affect the plateau region of the discharge voltage signal. This could be explained by the more sluggish diffusion of intercalated sodium-ions in the hard carbon structure. The first cycle of the cells showed a unique response in the optical spectra, suggesting that the fiber is sensitive to events during formation cycles, such as the solid electrolyte interphase formation.
Rheological behavior of ionomer dispersions and their incorporation in catalytic inks for use in PEMFC electrodes
(2023) Malmquist, Nora; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; Wickman, Björn; Ernst, Felix
Proton exchange membrane fuel cells produce greenhouse gas emission-free electric ity which is needed in the ongoing climate crisis. At the center of the fuel cell is a proton exchange membrane sandwiched between two electrodes produced from a catalytic ink. The ionomer component in catalytic inks acts both as a binder and a proton conductor and is an integral part of the catalyst layer. It is therefore im portant to have a thorough understanding of its key characteristics to optimize inks for improved processing and electrode performance and durability. Various perfluo rinated sulfonic-acid (PFSA) ionomer dispersions with varying solvent matrices and ionomer amounts were mixed and their viscosity was tested before and after elevated temperature treatment as it is known to support the dispersion process of specific ionomers in solvent matrices. Only short-side chained and low equivalent weight ionomers showed significant change in viscosity. Higher alcohol concentrations as well as more sterically hindering alcohols in the solvent matrix lead to more thicken ing. Higher ionomer concentrations, higher temperatures, and longer heating times also lead to thicker dispersions up to a maximum viscosity where it is fully gelled. The influence of ionomer viscosity on ink mixing and dispersion was described as well. Heating catalytic inks with short-side chained PFSA ionomers thickens the ink but the resulting electrode decals are full of holes. Inks made by mixing pre thickened ionomer with catalyst powder are difficult to mix and disperse properly. Using a more sterically hindering solvent will give a very thick ink even without any heating. The rheological properties of catalytic inks can be altered by changing the parameters that affect the structure of short-side chained and low equivalent weight PFSA ionomers but more investigation is needed into the dispersing of the inks as well as how altering of these parameters affect the resulting fuel cell performance. The increased understanding of the ionomer component will help to optimize the ink development and electrode design at PowerCell in the future which in turn will lead to more efficient fuel cells making them a more viable alternative to fossil fuel-based energy production.
Structural Characterization of Oxide Films Formed on Stainless Steel of Type 304L in Simulated PWR Primary Water
(2015) Fager, Cecilia; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied Physics
ABSTRACT Many different materials are used in Pressurized Water Reactors (PWR). In PWR high temperature high pressure corrosive environments a part of the corrosion products of these materials would release into the reactor coolant, some of which may get neutron activated to form a variety of radionuclides. The radionuclides, in the form of either solids or dissolved chemical species, circulate in reactor circuits and can deposit onto the oxide films being formed on the metal surfaces, leading to activity build-up in the plant and thus increases the dose rate. Zinc injection is known to be capable of reducing the corrosion rate of reactor materials and the activity build-up and is therefore being increasingly implemented in light water reactors worldwide. However, the fundamental mechanism behind the effects of zinc has not yet been fully understood. In this work the oxide films formed on three test coupons of stainless steel of type 304L that had been exposed to simulated PWR primary water conditions have been examined. Each test coupon had been subjected to different exposure environments such as with or without zinc injection, and Co-60 radiotracer was used to measure activity deposition rates under various water chemistry conditions. In order to understand the different activity deposition rates on the three test coupons, a structural characterization has been carried out using X-Ray Powder Diffraction (XRD), Laser Raman Spectroscopy (LRS), Scanning Electron Microscopy (SEM), equipped with Energy Dispersive X-ray Spectroscopy (EDS) and Focused Ion Beam (FIB), and High Resolution Analytical Transmission Electron Microscopy (HR ATEM). The presence of spinel phase (Me3O4) in all oxide films has been confirmed by the XRD and partly also by the LRS measurements. High resolution SEM topography examinations have revealed two kinds of surface oxide grains, (1) relatively large Fe-rich oxide crystals of regular shapes being sparsely distributed on the corroded surfaces, (2) tiny spherical Si-rich oxides which formed agglomerates locally. Cross-section examination with the FIB/SEM technique has revealed a thin oxide film, with a thickness of approximately 10 nm, inward growing crater oxides, with depth of approximately 200 nm, that were present beneath surface oxide grains. High resolution micrographs of the oxide films and zinc concentration profiles across the thin oxide films have also been obtained with HR ATEM. Combined with the present experimental findings the Point Defect Model (PDM) as developed by Macdonald has been used to explain the inhibition effect on the Co-60 incorporation in the oxide films by zinc injection. Suggestions for future work are also proposed.
The effect of PLGA nanoparticles on the osteogenic differentiation of hMSC
(2017) Dahlgren, Lukas; Chalmers tekniska högskola / Institutionen för fysik (Chalmers); Chalmers University of Technology / Department of Physics (Chalmers)
The polymer poly(lactic-co-glycolic acid) (PLGA) is both biocompatible and biodegradable and has therefore become one of the most frequently used polymers in the biomedical field. In this thesis, a literature study has been conducted on PLGA as a biomaterial. PLGA nanoparticles with a diameter of approximately 400 nm have been produced with the solvent evaporation method and the synthesis process has been analyzed and optimized. The synthesized nanoparticles have been used in in vitro studies on human mesenchymal stem cells, where their impact on cell viability and osteogenic differentiation has been investigated. For the nanoparticle synthesis, it was found that the concentration of stabilizer had the greatest impact on the result. Increased amount of stabilizer produced smaller particles. The in vitro studies were difficult to interpret, but implied that cell viability was negatively affected immediately after introduction of PLGA nanoparticles but that the cells quickly recovered. No difference in amount of expressed alkaline phosphatase, an osteogenic marker, could be observed between differentiated and non-differentiated samples. Deposits of extracellular calcium, another sign of osteogenesis, seemed to be enhanced by the particles upon visual inspection. However, this could not be proven quantitatively. These findings suggest that PLGA nanoparticles have an effect on the osteogenic differentiation of hMSCs, but the nature and extent of it needs to be investigated further.

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