24 results on '"Simon, Ulrich"'
Search Results
2. PTFE Enhances Discharge Performance of Carbon Cathodes in Potassium‐Oxygen Batteries**.
- Author
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Küpper, Jannis, Jakobi, Simon, and Simon, Ulrich
- Subjects
POLYTEF ,CATHODES ,POROSITY ,CORPORATE bonds ,ENERGY storage ,CARBON paper - Abstract
Potassium‐oxygen batteries (KOB) are a promising energy storage technology with high theoretical energy of 935 Wh/kg and long cycle life. Potential applications require the development of affordable cathode materials with high practical capacity. In this article, we show that low‐cost polytetrafluoroethylene (PTFE) treatment increases the discharge performance of a commercial carbon paper cathode. Cross‐sectional scanning electron microscopy reveals that PTFE alleviates mass transport limitations and facilitates homogeneous deposition of the discharge product potassium superoxide (KO2) within the cathode pore structure. Using electrochemical impedance spectroscopy, we found that PTFE, in combination with the appropriate electrolyte volume, can prevent pore flooding by the electrolyte. Free volume permits fast, gaseous oxygen transport throughout the cathode, which lowers mass transfer resistances and improves the rate capability. Moreover, PTFE enables high pore volume filling by KO2 and, in turn, high discharge capacity. Our results demonstrate that controlling the mass transport is essential for high‐performance cathodes for KOB. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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3. The effects of gold nanoparticles functionalized with ß-amyloid specific peptides on an in vitro model of blood–brain barrier.
- Author
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Ruff, J., Hüwel, S., Kogan, Marcelo J., Simon, Ulrich, and Galla, Hans-Joachim
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GOLD nanoparticles ,AMYLOID ,PEPTIDES ,BLOOD-brain barrier ,POLYETHYLENE glycol - Abstract
We studied the effect of gold nanoparticle (AuNP) size, surface charge, concentration and morphology on the integrity of the blood–brain barrier (BBB) in a well-established in vitro model set-up. We focused on the effect of peptide functionalized hollow gold nanospheres and gold nanorods, which selectively bind to amyloidogenic β -amyloid structures. These AuNP conjugates have already been successfully tested as photothermal absorbers for potential application in Alzheimer's disease (AD) therapy in an in vitro set-up, but may exhibit a low passage through the BBB due to their overall negative charge. Our results show that: (i) small (1.4 nm) AuNPs strongly affects the BBB integrity, (ii) negative surface charge impedes BBB passage, and (iii) this charge effect caused by the peptide is compensated by covalent coupling to a polyethylene glycol ligand stabilizing the particles in diluted manner. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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4. In Situ Spectroscopic Studies of Proton Transport in Zeolite Catalysts for NH3-SCR.
- Author
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Chen, Peirong and Simon, Ulrich
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PROTON transfer reactions , *ZEOLITE catalysts , *NITROGEN oxides - Abstract
Proton transport is an elementary process in the selective catalytic reduction of nitrogen oxides by ammonia (DeNOx by NH3-SCR) using metal-exchanged zeolites as catalysts. This review summarizes recent advancements in the study of proton transport in zeolite catalysts using in situ electrical impedance spectroscopy (IS) under NH3-SCR reaction conditions. Different factors, such as the metal cation type, metal exchange level, zeolite framework type, or formation of intermediates, were found to influence the proton transport properties of zeolite NH3-SCR catalysts. A combination of IS with diffuse reflection infrared Fourier transformation spectroscopy in situ (in situ IS-DRIFTS) allowed to achieve a molecular understanding of the proton transport processes. Several mechanistic aspects, such as the NH3-zeolite interaction, NO-zeolite interaction in the presence of adsorbed NH3, or formation of NH4+ intermediates, have been revealed. These achievements indicate that IS-based in situ methods as complementary tools for conventional techniques (e.g., in situ X-ray absorption spectroscopy) are able to provide new perspectives for the understanding of NH3-SCR on zeolite catalysts. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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5. In situ monitoring of DeNOx-SCR on zeolite catalysts by means of simultaneous impedance and DRIFT spectroscopy.
- Author
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Chen, Peirong, Schönebaum, Simon, Simons, Thomas, Rauch, Dieter, Moos, Ralf, and Simon, Ulrich
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ZEOLITE catalysts ,CATALYTIC reduction ,PROTON conductivity ,IMPEDANCE spectroscopy ,NITROGEN oxides ,COPPER compounds - Abstract
The development of more efficient zeolite catalyst for selective catalytic reduction of NO x (DeNO x -SCR) requires the analysis of the real-time state of the catalyst (e.g. NH 3 storage level) and the reaction mechanism. Impedance spectroscopy (IS) allows to electrically sense the uptake of NH 3 into proton conducting catalysts. By means of IS we reveal that Cu-SAPO possesses higher response to NH 3 than Cu-ZSM-5 over a broad temperature range from 80 °C to 450 °C. IS can thus be used to determine the NH 3 storage and to monitor the SCR reaction in situ . Simultaneous IS and DRIFTS study under in situ conditions unveiled that the proton conductivity of Cu-SAPO is related to the ammonium nitrate intermediate, NH 3 species bounded to both Cu sites and Brønsted acid sites. However, the contribution of each species to the conductivity varied in different reaction conditions. This correlation of integral electrical response with molecular processes paves a new route for the in situ monitoring and mechanistic understanding of zeolite-catalyzed SCR reactions. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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6. Correlating the Integral Sensing Properties of Zeolites with Molecular Processes by Combining Broadband Impedance and DRIFT Spectroscopy--A New Approach for Bridging the Scales.
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Peirong Chen, Schönebaum, Simon, Simons, Thomas, Rauch, Dieter, Dietrich, Markus, Moos, Ralf, and Simon, Ulrich
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ZEOLITES ,BROADBAND communication systems ,REFLECTANCE spectroscopy ,ELECTRIC impedance ,CATALYTIC activity - Abstract
Zeolites have been found to be promising sensor materials for a variety of gas molecules such as NH
3 , NOx , hydrocarbons, etc. The sensing effect results from the interaction of the adsorbed gas molecules with mobile cations, which are non-covalently bound to the zeolite lattice. The mobility of the cations can be accessed by electrical low-frequency (LF; mHz to MHz) and high-frequency (HF; GHz) impedance measurements. Recent developments allow in situ monitoring of catalytic reactions on proton-conducting zeolites used as catalysts. The combination of such in situ impedance measurements with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), which was applied to monitor the selective catalytic reduction of nitrogen oxides (DeNOx -SCR), not only improves our understanding of the sensing properties of zeolite catalysts from integral electric signal to molecular processes, but also bridges the length scales being studied, from centimeters to nanometers. In this work, recent developments of zeolite-based, impedimetric sensors for automotive exhaust gases, in particular NH3 , are summarized. The electrical response to NH3 obtained from LF impedance measurements will be compared with that from HF impedance measurements, and correlated with the infrared spectroscopic characteristics obtained from the DRIFTS studies of molecules involved in the catalytic conversion. The future perspectives, which arise from the combination of these methods, will be discussed. [ABSTRACT FROM AUTHOR]- Published
- 2015
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7. High-throughput experimentation in resistive gas sensor materials development.
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Belle, Clemens J. and Simon, Ulrich
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GAS detectors ,MATERIALS science ,IMPEDANCE spectroscopy ,METALLIC oxides ,NANOPARTICLE synthesis - Abstract
The review describes the workflow of a high-throughput screening process for the rapid identification of new and improved gas sensor materials. Multiple nanoparticulate metal oxides were synthesized via the polyol method, and material diversity was achieved by volume and/or surface doping. The resulting materials were applied as thick films on multielectrode substrates to serve as chemiresistors. This high-throughput approach including automated preparation, complex impedance measurements, and evaluation procedures enables reproducible measurements and their visual representation. Selected examples demonstrate the state of the art for applying high-throughput impedance spectroscopy in search of new sensitive and selective gas sensing materials as well as in analyzing structure–property relations. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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8. Gas sensing properties of volume-doped CoTiO3 synthesized via polyol method
- Author
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Siemons, Maike and Simon, Ulrich
- Subjects
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SEMICONDUCTOR doping , *ALDOSE reductase , *NANOPARTICLES , *GAS detectors - Abstract
Abstract: Volume-doped CoTiO3 was synthesized via the polyol method. As volume dopants Gd, Ho, K, La, Li, Na, Pb, Sb, and Sm with a concentration of 2at.% were applied. By X-ray diffraction (XRD) materials structure was confirmed, while the materials morphology was imaged using scanning electron microscopy (SEM). Thick films of the nanocrystalline material were applied with a laboratory robotic system to a 8×8 multielectrode substrate. We show that the p-type semiconducting material doped with various metals is applicable for the fast detection of ethanol and propylene. The volume dopants affect the sensing and response behavior of the base material. [Copyright &y& Elsevier]
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- 2007
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9. High throughput screening of the propylene and ethanol sensing properties of rare-earth orthoferrites and orthochromites
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Siemons, Maike and Simon, Ulrich
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ELECTROCHEMICAL analysis , *IMPEDANCE spectroscopy , *SPECTRUM analysis , *INTERFEROMETRY - Abstract
Abstract: Perovskite-type LnMO3 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; M=Cr, Fe) oxides were prepared by the polyol mediated synthesis. Thick films of the prepared materials were electrically characterised using high throughput impedance spectroscopy (HT-IS). All samples showed p-type semiconductivity. Ethanol and propylene were used to test the gas sensing behaviour in a temperature range from 200 to 500°C. A correlation between the (Ln–O) binding energy and the sensing properties is observed. [Copyright &y& Elsevier]
- Published
- 2007
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10. Preparation and gas sensing properties of nanocrystalline La-doped CoTiO3
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Siemons, Maike and Simon, Ulrich
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NANOPARTICLES , *IMPEDANCE spectroscopy , *SPECTRUM analysis , *SCANNING electron microscopy - Abstract
Abstract: p-Type semiconducting nanocrystalline CoTiO3:La (2at.%) was synthesized via polyol method. X-ray diffraction (XRD) was used to confirm the materials structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to image the materials morphology. Thick films of the nanocrystalline material were applied with a laboratory roboting system to an 8×8 multielectrode substrate, developed for high-throughput impedance spectroscopy (HTIS). With this method it was shown that the base material doped with various metals (Au, Ce, Ir, Pd, Pt, Rh, Ru) in different concentrations (0.2–0.6at.%) is applicable for the fast detection of ethanol, propylene and NO2, depending on the surface doping and the operation temperature. [Copyright &y& Elsevier]
- Published
- 2006
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11. Mobility of NH3-Solvated CuII Ions in Cu-SSZ-13 and Cu-ZSM-5 NH3-SCR Catalysts: A Comparative Impedance Spectroscopy Study.
- Author
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Rizzotto, Valentina, Chen, Peirong, and Simon, Ulrich
- Subjects
COPPER ions ,IMPEDANCE spectroscopy ,AMMONIA analysis ,CATALYTIC reduction ,ZEOLITE catalysts - Abstract
The mobility of NH
3 -solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NOx with NH3 (NH3 -SCR) over Cu-zeolite catalysts at low temperatures. Here, we utilize in situ impedance spectroscopy to explore the mobility of NH3 -solvated CuII ions, i.e., CuII (NH3 )n , in Cu-SSZ-13 and Cu-ZSM-5 zeolites with varied Cu ion exchange levels, and observed that both the zeolite framework (CHA or MFI) and the Cu exchange level influence the high-frequency dielectric relaxation processes that are associated with the short-range (local) motion of CuII (NH3 )n . Our results suggest that the local motion of CuII (NH3 )n species is favored within the CHA framework due to the unique cage structure, and thereby contribute to the overall ion conductivity at high frequencies, which, on the contrary, is not observed for ZSM-5, where NH3 -solvated Cu2+ ions do not experience a comparable constrained space for local motion. This study sheds new light on the mobility of Cu active sites under NH3 -SCR related reaction conditions and may contribute to an advanced understanding of the underlying mechanism. [ABSTRACT FROM AUTHOR]- Published
- 2018
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12. Size dependent gas sensing properties of spinel iron oxide nanoparticles
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Belle, Clemens J., Bonamin, Alberto, Simon, Ulrich, Santoyo-Salazar, Jaime, Pauly, Matthias, Bégin-Colin, Sylvie, and Pourroy, Geneviève
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IRON oxides , *NANOPARTICLES , *THICK films , *ELECTRODES , *GAS detectors , *IMPEDANCE spectroscopy , *TEMPERATURE - Abstract
Abstract: Spinel iron oxide nanoparticles of sizes from 12 to 60nm have been prepared via a hydrothermal synthesis. Thick films of the Fe3−x O4 nanoparticles deposited on interdigital electrodes were applied as resistive gas sensors. The electrical and gas sensing properties were characterized by impedance spectroscopy using multielectrode substrates. The reducing analytes CH4, NO, H2 and NH3 in N2 as a reference were applied in order to investigate the sensor response, the selectivity and the recovery behavior at temperature between 50°C and 300°C. The materials exhibit good sensor responses towards NH3 with low cross sensitivities towards H2 and NO at 250°C. A linearly increasing sensor response towards NH3 and H2 with decreasing particle size was found. [Copyright &y& Elsevier]
- Published
- 2011
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13. Advances in high throughput screening of gas sensing materials
- Author
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Siemons, Maike, Koplin, Tobias J., and Simon, Ulrich
- Subjects
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GAS analysis , *METALLIC oxides , *IMPEDANCE spectroscopy , *EXPERIMENTS - Abstract
Abstract: The workflow of a high throughput screening setup for the rapid identification of new and improved gas sensor materials is presented. The polyol method was applied to prepare nanoparticulate metal oxides as base materials. These materials have been modified by surface and volume doping. Using multielectrode substrates and high throughput impedance spectroscopy (HT-IS) a wide range of materials could be screened on a short time scale. Selected examples reflect the state of the art for applying HT-IS in search of new selective gas sensing materials. [Copyright &y& Elsevier]
- Published
- 2007
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14. Local dynamics of copper active sites in zeolite catalysts for selective catalytic reduction of NOx with NH3.
- Author
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Chen, Peirong, Khetan, Abhishek, Jabłońska, Magdalena, Simböck, Johannes, Muhler, Martin, Palkovits, Regina, Pitsch, Heinz, and Simon, Ulrich
- Subjects
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ACTIVITY of copper catalysts , *CATALYTIC reduction , *SELECTIVE catalytic oxidation , *ZEOLITE catalysts , *NITROGEN oxides emission control - Abstract
In Cu-zeolite based selective catalytic reduction of NO x with NH 3 (NH 3 -SCR), Cu species (in particular Cu I ) solvated by NH 3 molecules are predicted theoretically to be highly mobile with their mobility being decisive for the NH 3 -SCR reactivity at low temperatures (<250 °C). Direct experimental observation of the Cu mobility after NH 3 solvation, however, has not been achieved yet. Here we show that complex impedance-based modulus spectroscopy, performed by following the corresponding dielectric relaxation processes at high frequencies (10 4 to 10 6 Hz), can be applied to monitor directly the dynamic local movement of Cu ions in zeolite catalysts under NH 3 -SCR related reaction conditions. Simultaneous in situ impedance and infrared spectroscopy studies, assisted by periodic DFT calculations with reliable van der Waals dispersion corrections, allowed us to identify the key factors determining the local dynamics of Cu ions in two representative Cu-zeolites, i.e. Cu-ZSM-5 and Cu-SAPO-34. The co-adsorption and interaction of NO and NH 3 on Cu II sites led to the formation of highly mobile Cu I species and NH 4 + intermediates, and, consequently, significantly enhanced local dynamics of Cu ions in both zeolite catalysts. The re-oxidation of Cu I , which is the rate-determining step of NH 3 -SCR reaction, was more favorable in Cu-SAPO-34 than in Cu-ZSM-5, which can be attributed to the close coupling of NH 4 + intermediate and Cu site promoting the formation of Cu II -NO 2 /NH 4 + . As a result, the overall local dynamics of Cu, largely determined by Cu I species, is less dependent on the NH 4 + intermediate in Cu-SAPO-34 than in Cu-ZSM-5. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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15. Sol-Gel-Synthese, Tintenstrahldruck und Blitzlampentemperung von Tantaloxid-Dünnschichten zur pH-Messung
- Author
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Beale, Christopher Dyer, Offenhäusser, Andreas, Simon, Ulrich, and Ingebrandt, Sven
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impedance spectroscopy ,inkjet printing ,flash lamp annealing ,Ta2O5 ,sol-gel ,ddc:530 ,temperature sensor ,Tantalum ,ph sensor ,flexible electronics ,Ruthenium ,extended-gate field-effect transistor - Abstract
The measurement of pH and temperature plays an important role in many applications, including food analysis, environmental monitoring, chemical manufacturing, and medicine. Integration of pH and temperature sensors into packaging and electronic devices will continue to grow in importance as the world moves further towards Industry 4.0 and the Internet of Things, particularly as more industries become data-driven. New applications would also become possible by fabricating sensors on flexible substrates. Furthermore, building and operating a pH sensor without a reference electrode would provide many advantages, such as simpler manufacturing processes and long-term stability of the sensor. In a step towards achieving this goal, additive manufacturing of tantalum oxide films for pH sensing was explored in this work. Specifically, the sol-gel process and flash lamp annealing were used to deposit these films on gold metallized polyethylene terephthalate (PET) foils. After deposition of the sensing layers on the foil, both an extended-gate field-effect transistor (EGFET) and an impedimetric configuration were used to test the tantalum oxide layers for pH sensing. Additionally, a discovered negative temperature coefficient (NTC) in sol-gel derived ruthenium-tantalum oxide layers was examined for use as a temperature sensor, where the layers were thermally annealed with no photocuring on borosilicate wafer. In preparing the tantalum sol-gel solution for eventual layer deposition via photocuring, an optimized synthesis procedure for β-diketonate and β-ketoester complex formation with tantalum in 1,3-propanediol was conducted and the thin films characterized for photosensitivity in the near-UV range. Suboptimal synthesis procedures still work for device fabrication and were used in the production of the pH sensors. These solutions are stable in atmosphere, which is important for inkjet printing the solutions both in a laboratory and in an industrial environment. Inkjet printing of the solutions to form layers was then performed, followed by thermal annealing and flash lamp treatment of the layers. Photocured tantalum oxide layers derived from these solutions were characterized via various material characterization techniques. Exposure of the material to acidic and basic solutions in an EGFET configuration for pH sensing was also performed, and the layer was shown to withstand solutions in the range between pH 2 and pH 12.A photocured tantalum oxide layer was then tested for pH sensing in an impedimetric configuration on interdigitated electrodes (IDEs) without a reference electrode. A pH dependent double layer capacitance was found in solutions of high ionic strength. The data was fitted with an equivalent circuit consisting of a double layer capacitance in parallel with an interfering ion specific adsorption capacitance. Finally, the NTC of sol-gel derived ruthenium-tantalum oxide layers was characterized. A first material was tested from 20°C to 100°C, and then down to cryogenic temperatures. This was followed by investigating a second material, with an improved preparation procedure from the first material, and tested from -20°C to 60°C. In both cases, a reproducible NTC was observed which could potentially be combined as a temperature sensor with the fabricated pH sensor in a single device.
- Published
- 2022
16. Sensing catalytic conversion: Simultaneous DRIFT and impedance spectroscopy for in situ monitoring of NH3–SCR on zeolites.
- Author
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Simons, Thomas, Chen, Peirong, Rauch, Dieter, Moos, Ralf, and Simon, Ulrich
- Subjects
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CATALYTIC doping , *IMPEDANCE spectroscopy , *ZEOLITES , *PROTON conductivity , *CATALYSTS - Abstract
In order to meet the legislative emission requirements for NO x -containing exhaust gases, SCR catalysts, in particular zeolites, are used. To improve catalysts and the catalytic processes, an in-depth understanding of the reaction mechanisms is required as well as an analysis of the physicochemical properties of the SCR catalysts, preferably in real-time. Here, we introduce a setup combining impedance spectroscopy and infrared spectroscopy in diffuse reflection mode for in situ measurements on zeolites under SCR-related conditions. This setup allows for the first time to simultaneously monitor both, the proton conductivity of zeolites and the vibration modes of the molecules involved in the catalytic conversion of NO by NH 3 . We studied both, pure and Fe-promoted H-form zeolites, as sensors and model catalysts at the same time, and found out that weakly bound NH 3 is dominating the proton conductivity of both zeolites in a temperature range below the desorption temperature of NH 3 . When a part of the weakly bound NH 3 is consumed by the SCR reaction, proton conductivity and thus the sensing effect gets dominated by strongly bound NH 3 . This allows applying impedance spectroscopy to assess the degree of NH 3 loading and the state of the SCR conversion process in zeolite catalyst. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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17. In situ impedance spectroscopy for monitoring the mobility of cu active sites in zeolite catalysts for DeNO$_{x}$ NH$_{3}$-SCR
- Author
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Rizzotto, Valentina, Simon, Ulrich, Palkovits, Regina, and Chen, Peirong
- Subjects
impedance spectroscopy ,nitrogen oxides ,catalysis ,ddc:540 ,zeolites ,NH3-SCR ,cacatalysis - Abstract
Dissertation, RWTH Aachen University, 2020; Aachen : RWTH Aachen University 1 Online-Ressource (VIII, 159 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, Cu-exchanged chabazites (Cu-CHA) are the most relevant catalysts for the selective catalytic reduction (SCR) of NO$_{x}$ with NH$_{3}$ in automotive exhaust after-treatment. The mobility of NH$_{3}$-solvated Cu active sites [i.e. Cu$^{I}$/$^{II}$(NH $_{3}$)$_{n}$] in the CHA framework was recently found to be an essential element of the SCR catalytic cycle. Even though theoretical simulations agree on this crucial aspect, only the support of in situ analysis methods for the quantification of the ion mobility of Cu$^{I}$/$^{II}$(NH $_{3}$)$_{n}$ species can lead to a deeper understanding of the SCR mechanism in Cu-CHA catalysts. This work shows how in situ impedance spectroscopy (IS) is capable of detecting such local movement of Cu active sites in CHA. In situ IS was applied to monitor ion conduction processes under typical SCR reaction conditions by analysing the resonance peaks in the high-frequency range (HF). Initially, Cu-CHA were studied in NH$_{3}$ atmosphere in order to ensure the presence of NH$_{3}$-solvated Cu$^{2+}$ and evaluate its specific interaction with the CHA framework. Afterwards, the complexity of the study was increased by performing in situ IS measurements in gas atmospheres that initiate the SCR reaction and the Cu $^{2+}$/Cu$^{+}$ redox cycle. In a third step, the site-specific mobility of Cu$^{I}$/$^{II}$(NH $_{3}$)$_{n}$ was investigated by analysing two Cu-CHA materials in which Cu coordinates only to isolated or paired Al sites, respectively. In this way, the short-range motion of Cu$^{I}$/$^{II}$(NH $_{3}$)$_{n}$ was successfully monitored by variations of the HF resonance frequency. The observed mobility trends agree with those predicted by theoretical simulations. Moreover, it was for the first time possible to discriminate the contribution to the overall ion conductivity given by Cu$^{I}$/$^{II}$(NH $_{3}$)$_{n}$ from the one given by other NH$_{3}$-solvated species formed during SCR, like NH$_{4}$$^{+}$. The results obtained by in situ IS were subsequently used to interpret the behaviour of Cu-CHA in the NH$_{3}$-sensing and to optimise their SCR catalytic performances. It was revealed that the Cu mobility alters NH$_{3}$-sensing response of Cu-CHA in SCR conditions, and a pretreatment under reducing conditions was found beneficial to enhance the catalytic performances of a commercial Cu-CHA. Finally, a novel microwave-assisted method for the synthesis of the chabazite SSZ-13 was developed, which allowed to reduce the conventional reaction time and to obtain materials with tailored composition and structure for future in situ investigations., Published by RWTH Aachen University, Aachen
- Published
- 2020
18. Sulfonated poly(ether ether ketone)–silica membranes doped with phosphotungstic acid. Morphology and proton conductivity
- Author
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Colicchio, Irene, Wen, Fei, Keul, Helmut, Simon, Ulrich, and Moeller, Martin
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ARTIFICIAL membranes , *KETONES , *PROTONS , *METHANOL , *FUEL cells , *TRANSMISSION electron microscopy , *IMPEDANCE spectroscopy - Abstract
Abstract: Sulfonated poly(ether ether ketone) (SPEEK)–silica membranes doped with phosphotungstic acid (PWA) are presented. The silica is generated in situ via the water free sol–gel process of polyethoxysiloxane (PEOS), a liquid hyperbranched inorganic polymer of low viscosity. At 100°C and 90% RH the membrane prepared with PEOS (silica content=20wt%) shows two times higher conductivity than the pure SPEEK. The addition of small amounts of PWA (2wt% of the total solid content) introduced in the early stage of membrane preparation brings to a further increase in conductivity (more than three times the pure SPEEK). During membrane formation PWA and the sulfonic acid groups of SPEEK act as catalysts in the conversion of PEOS in silica. Once the membranes are formed, PWA is incorporated in the silica network and acts as proton conductivity enhancer. The correlation between morphology and proton conductivity allows establishing the optimal doping level and preparation procedure. The morphology is studied by transmission electron microscopy (TEM) while the proton conductivity is measured by impedance spectroscopy (IS). The direct methanol fuel cell performance is also investigated. [Copyright &y& Elsevier]
- Published
- 2009
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19. Correlation of TPD and impedance measurements on the desorption of NH3 from zeolite H-ZSM-5
- Author
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Rodríguez-González, Luz, Rodríguez-Castellón, Enrique, Jiménez-López, Antonio, and Simon, Ulrich
- Subjects
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THERMAL desorption , *IMPEDANCE spectroscopy , *STATISTICAL correlation , *AMMONIA , *ZEOLITES , *ELECTRIC conductivity , *HOPPING conduction - Abstract
Abstract: We compare the characteristic features obtained in TPD and in impedance measurements on the desorption of ammonia from zeolite H-ZSM-5. We show that the ammonia desorption peaks observed by TPD correspond to characteristic changes in the proton transport mechanism. While at low temperature an almost temperature independent Grotthus-like proton conductivity in the presence of ammonia is observed, the on-set of the low temperature desorption peak in TPD coincides with a change in the transport mechanism to a vehicle-mediated transport of protons. Furthermore, at higher temperature, the desorption of ammonia from the Brønsted acid sites, as indicated by the high temperature peak in TPD, causes again a characteristic change in the temperature dependent conductivity, reflected by a decreasing conductivity with increasing temperature in an intermitted range, which then turns over again to simply activated proton hopping. [Copyright &y& Elsevier]
- Published
- 2008
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20. Zeolite based trace humidity sensor for high temperature applications in hydrogen atmosphere
- Author
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Neumeier, Stefan, Echterhof, Thomas, Bölling, Ralf, Pfeifer, Herbert, and Simon, Ulrich
- Subjects
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ZEOLITES , *HYDROGEN , *IMPEDANCE spectroscopy , *DETECTORS - Abstract
Abstract: We present a humidity sensor based on H-ZSM-5 type zeolite that is suitable to detect traces of humidity (∼10–110ppmV) under harsh conditions, e.g. reducing atmosphere (H2) and high temperature (up to 600°C). By means of complex impedance spectroscopy (IS) we show that the zeolite sensor responds linearly towards minimal changes in humidity. Therefore this result indicates that the zeolite sensor is capable to detect traces of humidity in processes where high temperatures in a hydrogen environment are required. [Copyright &y& Elsevier]
- Published
- 2008
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21. Korrelation von integralen und lokalen Untersuchungsmethoden an Abgasnachbehandlungssystemen für Magermotoren
- Author
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Schönebaum, Simon, Simon, Ulrich, and Moos, Ralf
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exhaust gas treatment ,impedance spectroscopy ,nitrous oxides ,DRIFTS ,ddc:540 ,Stickoxide ,in situ ,Abgasnachbehandlung ,Impedanzspektroskopie ,infrared spectroscopy ,Infrarotspektroskopie - Abstract
Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (xiii, 137, XXXIII Seiten) : Illustrationen, Diagramme (2019). = Dissertation, RWTH Aachen University, 2019, In this work the use of DRIFT spectroscopy for the investigation of molecular processes on different catalytic converters for exhaust gases of lean burn engines was investigated. The results were correlated with the outcomes of different integral measurement methods. By that, a better understanding of underlying processes resulting in certain integral observations was approached. With the help of DRIFT spectroscopy, the interpretation of HF-IS measurements on a SCR converter was improved: The already known correlation of resonance frequency and the mobility of adsorbed NH3 species was sharpened by a precise definition of the kind of mobile species. In addition to that, the influence of highly mobile [CuI(NH3)2]+ complexes on the resonance frequency was proofed. During this work, initial experiments for the correlation of integral and local investigation methods on several, technically relevant LNTs were performed. First, detailed DRIFTS investigations were correlated with high-resolution methods for material analysis such as TEM-EDX to obtain detailed information about cross effects between the different compounds and their de- or increase by different converter architectures. The results were then correlated with catalytical tests. The correlation showed a critical impact of ceria as well as barium-containing components on the NOx storage behavior. Additionally, the time-resolved formation as well as decomposition of different reaction intermediates as well as products in dependence of different LNT compositions was investigated. By that, the interpretation of measurement results from laboratory gas test bench were improved: The observed high NOx storage of one investigated catalyst was traced back to very high precious metal dispersion over the active components. Also, the use of ceria as low temperature NOx-storage was found to be critical for the performance of the LNTs during regeneration as it increases the direct oxidation of hydrocarbons and by this lowers the regeneration performance of the LNT. Additionally, an optimal dispersion of precious metals and BaCO3 were identified to be crucial to the systems performance. In the last chapter of this work the desorption of 1-Octanol from a oxidation catalyst was investigated by TP-DRIFTS. With the help of these investigations, the formation of any liquid phase during adsorption was excluded and the decomposition processes of 1-Octanol during TPO experiments were confirmed with the help of observed intermediates., Published by Aachen
- Published
- 2019
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22. Darstellung, Modifizierung und elektrische Charakterisierung von Silizium-Nanopartikeln
- Author
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Nelles, Jürgen and Simon, Ulrich
- Subjects
Silizium-Nanopartikel ,impedance spectroscopy ,silicon nanoparticle ,nanotechnology ,ddc:540 ,Chemie ,Druckbare Elektronik ,Impedanzspektroskopie ,printable electronics ,Nanotechnologie - Abstract
This thesis is motivated by the idea, to implement functional building blocks with silicon nanoparticles by means of printable electronics. Hence, the topic of this work is the investigation of the charge transport in thin layers made of silicon nanoparticles. As model systems commercially available as well as self prepared silicon nanoparticles were used and modified with different organic surface functionalities. In the first part of this work the surface modification of commercially available silicon nanoparticles synthesized in the gas phase is described: Initially, the surface oxide of the 20 nm large nanoparticles was removed by means of etching with acidic fluorine-containing solutions. Subsequently, the resulting hydrogen-terminated surface was modified via hydrosilylation using different 1-alkenes. In the second part of this work the preparation of modified silicon nanoparticles in liquid phase is observed: Based on silicon tetrachloride hydrogen-terminated silicon nanoparticles with a size between 1.2 nm and 4.5 nm as well as chlorine-terminated silicon nanoparticles with a size between 2 nm and 6 nm wered synthesized as intermediate and subsequently modified using hydrosilylation or silanization, respectively. The electrical characterization of thin layers made of modified silicon nanoparticles was performed using impedance spectroscopy. With regard to apply modified silicon nanoparticles as active material using printable electronics it was shown that the electrical transport in thin and compact layers made of the nanoparticles is thermically activated and, in the relevant area of room temperature, could be described using an ARRHENIUS approach. The activation energies were in the range of a half electron volt and could be influenced by thickness and permittivity of the organic modification. As electron transport mechanism nearest neighbor hopping was identified, as it was expected for a statistically distribution of localized states in the considered temperature range.
- Published
- 2010
23. Entwicklung und Anwendung von Hochdurchsatztechniken zur Darstellung und Untersuchung neuer nanostrukturierter Sensormaterialien
- Author
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Koplin, Tobias Joachim and Simon, Ulrich
- Subjects
Metal Oxide Gassensor ,Nanoparticle ,High throughput screening ,Impedance Spectroscopy ,ddc:540 ,Metalloxid-Gassensor ,Chemie ,Gassensor ,Impedanzspektroskopie ,Nanopartikel - Abstract
For the development of new gas sensor materials surface and volume doped nanoscalic metal oxides were investigated, whereas high-throughput techniques were applied. The necessary synthesis and characterisation methods were provided by modification of a pipetting robot for a parallel material synthesis and sample deposition on special multi-electrode substrates, as well as the further development of a screening reactor and single sensor test station. Making use of the polyol method opened a simple synthetic access to nanoscalic metal oxides like ZnO, In2O3 and SnO2, which were used as basic materials for the preparation of highly diverse functionalised surface and volume doped material libraries. To acquire their sensoric properties a screening program was used which comprised of test gases of H2, CO, NO, NO2 and C3H6 in synthetic air in the temperature range from 523 to 673 K. To analyse the resulting high amounts of data the Q/S-plot was developed and applied, which enables by comparing the relative selectivity and sensitivity a fast visual identification of the best promising material combinations. As an example doping by silver cluster led to a distinct increase of the sensitivity of various metal oxides against hydrogen; a mixture of rhodium, gold and palladium increased the sensoric properties of SnO2 towards the detection of CO, whereas using silver as a dopant increased distinctly the response to NO2. These screening results were further investigated by making use of single sensor elements, whereas e.g. the silver doped SnO2 showed an extrapolated limit of detection of about 100 ppb of NO2.
- Published
- 2007
24. Entwicklung einer neuen Methode zur impedanzspektroskopischen Erfassung der temperaturprogrammierten Desorption von Ammoniak in H-Form Zeolithen
- Author
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Rodríguez-González, Luz and Simon, Ulrich
- Subjects
Ammoniaksensor ,temperaturprogrammierte Desorption ,temperature-programmed desorption ,ddc:540 ,Zeolith ,Chemie ,ammonia sensor ,Impedance spectroscopy ,H-ZSM-5 ,zeolite ,Impedanzmessung - Abstract
This PhD thesis deals with the development of a measuring system, that allows determining, in analogy to the well-known temperature-programmed desorption measurement of NH3 (NH3-TPD), the acidic properties of zeolites (H-ZSM-5 with SiO2/Al2O3 ratios from 30 to 1000). This new method, denoted IS-TPD, is based on a combination of NH3-TPD with impedance spectroscopy measurements (IS). The IS-TPD new method, with a zeolite sensor, is used for the NH3 detection instead of the usual one based on gas chromatography, whose functionality is based on the impedance spectroscopic measurement of the proton conductivity. With these developments it was possible to refinement the known mechanistic picture to the adsorption behaviour of NH3 in H-form-zeolites, which finally led to a new understanding of the functional principle of NH3-Sensors based on H-form-zeolites. Both impedance and NH3-TPD measurements were accomplished to provide a basis for the methodical development of the IS-TPD. The results of these measurements as well as the detailed picture of a model for the ammonia supported proton transport, which were developed in the so far completely independently regarded methods, provided a consistent picture of the supported proton transport mechanism in zeolites. Hence, the transition of a Grotthus-like, vehicle and hopping mechanisms, respectively, depending on the loading of the sample with NH3, was derived from the impedance measurements. These are compatible with the interpretation of the NH3-TPD profiles. This again forms the basis for the following combination of the two methods for the development of a new IS-TPD measuring system. Therein, the zeolite samples were coated in form of a thick-film on a directly heated inter-digital capacitor (idc) chip, with which the sample quantity was reduced of approximately 80 mg by the NH3-TPD to 0,5 mg. The outcome of this was a clearly smaller time of contact with same flow rate. This was manifested in a shift of the desorption maxima around 60°C (for the low temperature (LT) peak) and around 90°C (for the high temperature (HT) peak) and is to be explained by decreased readsorption. Furthermore it was found that the quantity of desorbed NH3 became smaller for each Brønsted acid site with decreasingly SiO2/Al2O3 ratios. This disagreed in first glance to the assumption that the samples were saturated with NH3. Hence, a new model picture for the functionality of the zeolite sensors was derived, which included the fact that the saturation measured by means of IS corresponds presumanly just to a saturation within surface-near range, which in this work was denoted “electrical saturation”. Accordingly, the samples will already achieve a constant impedance value in ammonia, if the conductivity within near-surface by far exceeds the volume saturation. In this case a further volume saturation obviously does not lead to a further increase of the conductivity. For model verification in the new IS-TPD measuring system the zeolites H-Y and H-beta were investigated, which showed similar behaviour than H-ZSM-5. Thus the work represents a new experimental basis for the characterisation of Brønsted acid sites in solids.
- Published
- 2007
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