5 results
Search Results
Now showing 1 - 5 of 5
- ItemInfluence of molecular weight of polycation polydimethyldiallylammonium and carbon nanotube content on electric conductivity of layer-by-layer films(Amsterdam [u.a.] : Elsevier, 2022) Neuber, Sven; Sill, Annekatrin; Efthimiopoulos, Ilias; Nestler, Peter; Fricke, Katja; Helm, Christiane A.For biological and engineering applications, nm-thin films with high electrical conductivity and tunable sheet resistance are desirable. Multilayers of polydimethyldiallylammonium chloride (PDADMA) with two different molecular weights (322 and 44.3 kDa) and oxidized carbon nanotubes (CNTs) were constructed using the layer-by-layer technique. The surface coverage of the CNTs was monitored with a selected visible near infrared absorption peak. Both the film thickness and the surface coverage of the CNTs increased linearly with the number of CNT/PDADMA bilayers deposited (film thickness up to 80 nm). Atomic force microscopy images showed a predominantly surface-parallel orientation of CNTs. Ohmic behavior with constant electrical conductivity of each CNT/PDADMA film and conductivity up to 4 · 103 S/m was found. A change in PDADMA molecular weight by almost a factor of ten has no effect on the film thickness and electrical conductivity, only the film/air roughness is reduced. However, increasing CNT concentration in the deposition dispersion from 0.15 up to 0.25 mg/ml results in an increased thickness of a CNT/PDADMA bilayer (by a factor of three). The increased bilayer thickness is accompanied by a decreased electrical conductivity (by a factor of four). The decreased conductivity is attributed to the increased monomer/CNT ratio.
- ItemChemical insights into the base-tuned hydrothermal treatment of side stream biomasses(Cambridge : Royal Society of Chemistry, 2022) Tkachenko, Vitalii; Marzban, Nader; Vogl, Sarah; Filonenko, Svitlana; Antonietti, MarkusHerein, we analyzed the hydrothermal processes applied to four very different side stream biomasses (chestnut foliage, sugar beet pressing chips, pine bark and branches from park cleaning, bamboo cuts) and identified diverse soluble products depending on the starting pH of the reaction, covering mild to strong basic pH conditions. Despite the biological diversity of the starting products, hydrothermal disintegration of biomass results in a remarkable reduction of chemical diversity towards a controllable number of molecular products, and the well-resolved and rather simple NMR-spectra allow the assignment of the products to only a few families of compounds. It has been revealed that in comparison with the classical hydrothermal treatment, where mostly hydrochar is produced, molar excess of base shifts the hydrothermal treatment towards a humification process. A further increase of the base content causes destruction of the biomass into the more oxygenated homogeneous colloid and thus, for the first time, it can be assigned to the hydrothermal fulvication process. We discuss diverse valorization schemes depending on the biomass and conditions applied.
- ItemLocal Structure Investigation of Cu Precipitates in Modified 18CrNiMo7-6 Steels by Synchrotron X-ray Absorption Spectroscopy(Tōkyō : ISIJ, 2022) Suwanpinij, Piyada; Bambach, Margarita; Bootchanont, Atipong; Sailuam, WutthigraiThis paper studied the copper precipitation in an 18CrNiMo7-6 martensitic steel (0.19 mass% C) with copper addition and its resulting improved mechanical behavior. The development of nano-precipitates in two modified alloys with 1.0 and 1.5 mass% copper addition was investigated by means of synchrotron X-ray absorption spectroscopy. The first-principles calculation has enabled the modeling of the unavailable copper standards: solid solution, B2, BCC, 2H, 9R and 3R, for calculating the XAS spectra and successfully identified the unknown phases after aging for the first time in this steel group. The samples alloyed with 1.5 mass% copper yielded the semi-coherent 9R structure when aged at 500°C between 166 to 360 minutes. The ones containing 1 mass% copper formed the B2 ordered structure after aging at 480°C for 50 minutes and revealed the co-existence of the 9R after 240 minutes. The analysis reveals the precipitation kinetics of copper in low carbon martensitic steel and helps determine the optimum tempering parameters to adjust peak strength.
- ItemGreen hydrogen from anion exchange membrane water electrolysis: A review of recent developments in critical materials and operating conditions(Cambridge : Royal Society of Chemistry, 2020) Miller, Hamish Andrew; Bouzek, Karel; Hnat, Jaromir; Loos, Stefan; Bernäcker, Christian Immanuel; Weißgärber, Thomas; Röntzsch, Lars; Meier-Haack, JochenHydrogen production using water electrolysers equipped with an anion exchange membrane (AEM), a pure water feed and cheap components such as platinum group metal-free catalysts and stainless steel bipolar plates (BPP) can challenge proton exchange membrane (PEM) electrolysis systems as the state of the art. For this to happen the performance of the AEM electrolyzer must match the compact design, stability, H2purity and high current densities of PEM systems. Current research aims at bringing AEM water electrolysis technology to an advanced level in terms of electrolysis cell performance. Such technological advances must be accompanied by demonstration of the cost advantages of AEM systems. The current state of the art in AEM water electrolysis is defined by sporadic reports in the academic literature mostly dealing with catalyst or membrane development. The development of this technology requires a future roadmap for systematic development and commercialization of AEM systems and components. This will include basic and applied research, technology development & integration, and testing at a laboratory scale of small demonstration units (AEM electrolyzer shortstacks) that can be used to validate the technology (from TRL 2-3 currently to TRL 4-5). This review paper gathers together recent important research in critical materials development (catalysts, membranes and MEAs) and operating conditions (electrolyte composition, cell temperature, performance achievements). The aim of this review is to identify the current level of materials development and where improvements are required in order to demonstrate the feasibility of the technology. Once the challenges of materials development are overcome, AEM water electrolysis can drive the future use of hydrogen as an energy storage vector on a large scale (GW) especially in developing countries. © The Royal Society of Chemistry 2020.
- ItemSpontaneous fluctuations in a plasma ion assisted deposition – correlation between deposition conditions and vanadium oxide thin film growth(Amsterdam [u.a.] : Elsevier, 2021) Frank, Anna; Dias, Miguel; Hieke, Stefan; Kruth, Angela; Scheu, ChristinaIn this work correlations between thin film crystallinity of plasma ion assisted electron beam evaporated vanadium oxide (VOx) and fluctuations of the deposition parameters during the growth process could be observed by in situ monitoring deposition conditions and electron microscopy studies. In the presented case, unintentional fluctuations in the gas flow at the plasma source caused by inhomogeneous melting of the target material lead to an increase in discharge current and therefore a decrease of the oxygen flow in the plasma source, resulting in the formation of highly crystalline bands due to a temporary increase in energy flux. The major part of the VOx thin film consists of a large number of nanocrystals embedded in an amorphous phase. In-depth structural analysis confirms a mixture of V2O5, in different modifications, VO2, as well as the mixed-valence oxides V4O9 and V6O13, for nanocrystalline parts and crystalline bands. These differ mainly in the degree of crystallinity being influenced by variations in discharge current, and partly in the amount of higher oxidized vanadium oxides. In future, precisely controlled variation of plasma source conditions will open up pathways to control and tailor crystallinity of electron beam evaporated thin films, allowing for production methods for patterned thin films or layers with graduated crystallinity. This may give rise to a new class of coatings of nanohybrids combining amorphous VOx with low electrical conductivity and crystalline domains providing a higher electrical conductivity which is useful for electrochromic displays, smart windows, and solar cells.