TY - JOUR A1 - Seiß, Volker A1 - Thiel, Susanne A1 - Eichelbaum, Maik T1 - Preparation and Real World Applications of Titania Composite Materials for Photocatalytic Surface, Air, and Water Purification: State of the Art JF - Inorganics N2 - The semiconducting transition metal oxide TiO2 is a rather cheap and non-toxic material with superior photocatalytic properties. TiO2 thin films and nanoparticles are known to have antibacterial, antiviral, antifungal, antialgal, self, water, and air-cleaning properties under UV or sun light irradiation. Based on these excellent qualities, titania holds great promises in various fields of applications. The vast majority of published field and pilot scale studies are dealing with the modification of building materials or generally focus on air purification. Based on the reviewed papers, for the coating of glass, walls, ceilings, streets, tunnels, and other large surfaces, titania is usually applied by spray-coating due to the scalibility and cost-efficiency of this method compared to alternative coating procedures. In contrast, commercialized applications of titania in medical fields or in water purification are rarely found. Moreover, in many realistic test scenarios it becomes evident that the photocatalytic activity is often significantly lower than in laboratory settings. In this review, we will give an overview on the most relevant real world applications and commonly applied preparation methods for these purposes. We will also look at the relevant bottlenecks such as visible light photocatalytic activity and long-term stability and will make suggestions to overcome these hurdles for a widespread usage of titania as photocalyst. KW - TiO2 photocatalysis; semiconductor thin films; antiviral and antibacterial properties; air purification; water purification; easy-to-clean effect; disinfection Y1 - 2022 U6 - https://doi.org/10.3390/inorganics10090139 SN - 2304-6740 VL - 10 IS - 9 PB - MDPI AG ER - TY - JOUR A1 - Birkner, Lena A1 - Eichelbaum, Maik T1 - Validation of Voltammetric Methods for Online Analysis of Platinum Dissolution in a Hydrogen PEM Fuel Cell Stack JF - Electrochem N2 - Platinum dissolution in PEM fuel cells is an increasingly important indicator for the state-of-health and lifetime prediction of fuel cells in real applications. For this reason, portable online analysis tools are needed that can detect and quantify platinum with high sensitivity, selectivity, and accuracy in the product water of fuel cells. We validated the hanging mercury drop electrode (HMDE) and non-toxic bismuth film electrodes for the voltammetric determination of platinum for this purpose. Bismuth films were prepared by reductive deposition on both a glassy carbon solid state electrode and on a screen-printed electrode (film on-chip electrode). Both bismuth film electrodes could be successfully validated for the determination of platinum by adsorptive stripping voltammetry. An LOD of 7.9 μg/L and an LOQ of 29.1 μg/L were determined for the bismuth film solid state electrode, values of 22.5 μg/L for the LOD and of 79.0 μg/L for the LOQ were obtained for the bismuth film on-chip electrode. These numbers are still much higher than the results measured with the HMDE (LOD: 0.76 ng/L; LOQ: 2.8 ng/L) and are not sufficient to detect platinum in the product water of a fuel cell run in different load tests. The amount of dissolved platinum produced by a 100 W fuel cell stack upon dynamic and continuous high load cycling, respectively, was in the range of 2.9–4.1 ng/L, which could only be detected by the HMDE. Y1 - 2022 U6 - https://doi.org/10.3390/electrochem3040048 SN - 2673-3293 VL - 3 IS - 4 SP - 728 EP - 745 PB - MDPI AG ER - TY - JOUR A1 - Thiel, Susanne A1 - Eichelbaum, Maik T1 - Scanning electrochemical microscopy for the differentiation of radical-induced degradation mechanisms in polymer electrolyte membranes JF - RSC Advances N2 - In this work, a spatially resolved analytical method based on scanning electrochemical microscopy (SECM) to distinguish different degradation phenomena in polymer electrolyte membranes was developed. SECM was combined with a Franz diffusion cell to distinguish between radical-induced aging of a sulfonated tetrafluoroethylene based fluoropolymer-copolymer due to deactivation of the sulfonic acid groups followed by a decreased proton conductivity, and the radical-induced formation of cracks and holes in the polymer. The experiments were performed with ferrocyanide as redox mediator to detect holes and cracks, and protons (sulfuric acid) to determine the through-plane proton conductivity, respectively. A pristine Nafion™ membrane, a pristine Nafion™ membrane with an artificial pinhole and a Nafion™ membrane aged with Fenton's reagent were investigated to prove the measurement principle. It could be shown that holes and cracks can be reliably detected with this approach and discriminated from a change in proton conductivity. The presence of holes in the investigated aged membranes was confirmed by scanning electron microscopy, whereas the loss of sulfonate groups could be supported by infrared spectroscopy measurements. Y1 - 2024 U6 - https://doi.org/10.1039/d4ra02203c SN - 2046-2069 VL - 14 IS - 20 SP - 13748 EP - 13757 PB - Royal Society of Chemistry (RSC) ER - TY - JOUR A1 - Heenemann, Maria A1 - Millet, Marie-Mathilde A1 - Girgsdies, Frank A1 - Eichelbaum, Maik A1 - Risse, Thomas A1 - Schlögl, Robert A1 - Jones, Travis A1 - Frei, Elias T1 - The Mechanism of Interfacial CO2 Activation on Al Doped Cu/ZnO JF - ACS Catalysis N2 - We report on a combined quantitative charge carrier and catalytic activity analysis of Cu/ZnO(:Al) model catalysts. The promoting effect of Al3+ on the ZnO support for CO2 activation via the reverse water–gas-shift reaction has been investigated. The contact-free and operando microwave Hall Effect technique is applied to measure charge carriers in Cu/ZnO(:Al) based model catalysts under reverse water–gas shift reaction conditions. This method allows us to monitor the electrical conductivity, charge carrier mobility, and absolute number of charge carriers. An increase in charge carrier concentration with increasing Al3+ content and its direct correlation with the catalytic activity for CO formation is found. We conclude that the increased availability of charge carriers plays a key role in CO2 activation and CO formation, which finds additional support in a concurrent decrease of the apparent activation energy and increase in the reaction order of CO2. In combination with comprehensive DFT calculations, the impact of the interfacial charge transfer, coupled to oxygen defect sites in ZnO and CO2 adsorption properties, is elucidated and highlighted. In conclusion, the results from this operando investigation combined with DFT calculations demonstrate the importance of charge transfer processes as decisive descriptors for understanding and explaining catalytic properties. KW - CO2 activation Al doped Cu/ZnO charge carrier quantification Cu−ZnO interface rWGS activity Y1 - 2020 U6 - https://doi.org/10.1021/acscatal.0c00574 SN - 2155-5435 VL - 10 IS - 10 SP - 5672 EP - 5680 PB - American Chemical Society (ACS) ER - TY - JOUR A1 - Thiel, Susanne A1 - Eichelbaum, Maik T1 - Spatially Resolved Differentiation of Functional Degradation and Perforating Structural Defects in Membrane Electrode Assemblies Using Diffusion-Cell Coupled DC-SECM JF - ACS Measurement Science Au N2 - In order to increase the lifetime of polymer electrolyte membrane (PEM) fuel cells (PEMFCs) and water electrolyzers (PEMWEs), understanding local degeneration processes in membrane electrode assemblies (MEAs) is crucial. By a combination of scanning electrochemical microscopy (SECM) with a flow-through diffusion cell (DiffC-DC-SECM) and ferrocyanide and protons as redox mediators, a spatially resolved analytical method was developed that can differentiate between different functional and structural degeneration phenomena in the aging process of a membrane. An SECM scan at cathodic potential detects the diffusion of protons through the membrane and thus its through-plane proton conductivity, while a second SECM scan at anodic potential visualizes the diffusion of the iron complex through the membrane, thus perforating structural damage such as cracks and holes. The method was successfully validated for the spatially resolved differentiation of membrane damage in pristine PEMs and catalyst-coated membranes (CCMs) with artificial holes, chemically aged CCMs, and MEAs in fully assembled operational PEMFCs aged by an open-circuit voltage membrane accelerated stress test. DiffC-DC-SECM thus provides a powerful technique with high local resolution for membrane integrity testing under realistic operation conditions to develop long-term durable materials for PEMFCs and PEMWEs. Y1 - 2025 U6 - https://doi.org/10.1021/acsmeasuresciau.5c00071 SN - 2694-250X VL - 5 IS - 5 PB - American Chemical Society (ACS) ER - TY - CHAP A1 - Thiel, Susanne A1 - Seis, Volker A1 - Eichelbaum, Maik T1 - Scanning electrochemical microscopy for the characterization of fuel cell components T2 - 2022 International Workshop on Impedance Spectroscopy (IWIS) N2 - The limited lifetime and severe degradation after long-term usage of polymer electrolyte membrane fuel cells (PEMFCs) are challenges that have to be overcome, if PEMFCs are to play the anticipated major role in a sustainable energy and transportation system based on green hydrogen. Therefore, analytical scanning methods to precisely characterize and understand the degradation and ageing mechanisms with high spatial resolution are essential. We are using and validating scanning electrochemical microscopy (SECM) as tool for detecting descriptors of the electrochemical performance of PEMFCs treated under different activation and ageing protocols. For this purpose, a pristine Nafion™ membrane, which is typically used as proton exchange membrane (PEM) in low temperature fuel cells, was activated and deactivated after well-defined protocols to demonstrate the fundamental suitability of SECM for investigating PEMFC components. Our results indicate that the impedance associated with the proton conductivity of the Nafion™ membrane as measured by SECM was dependent on the pretreatment of the membrane and increased in the following order: hot water < hydrochloric acid < sulfuric acid. The partial and complete deactivation of the membrane using Fenton’s reagent and barium hydroxide, respectively, could be spatially visualized with SECM as well. In addition, we investigated a PEM as part of a complete membrane electrode assembly in a fully functional PEMFC after accelerated ageing tests and could identify an increased local PEM impedance by SECM. All trends could be confirmed by electrochemical impedance spectroscopy (EIS). Moreover, we investigated a typical gas diffusion layer (GDL) of a PEMFC with SECM. As a result, the microporous side of the GDL showed a much lower impedance than its macroporous side, which is comprehensible since it agrees with the additional carbon black coating on the former side. KW - electrochemical microscopy, fuel cell, polymer electrolyte membrane, gas diffusion layer, degradation, electrochemical impedance spectroscopy Y1 - 2022 U6 - https://doi.org/10.1109/IWIS57888.2022.9975128 SP - 14 EP - 19 PB - IEEE ER - TY - CHAP A1 - Rostan, Katharina A1 - Kruglov, Roman A1 - Seiß, Volker A1 - Thiel, Susanne A1 - Eichelbaum, Maik A1 - Engelbrecht, Rainer T1 - In-situ Temperature and Humidity Measurement in PEM Fuel Cells with Off-the-shelf FBG T2 - 28th International Conference on Optical Fiber Sensors N2 - We propose a cost efficient fiber Bragg grating (FBG) sensor for measuring temperature and humidity in polymer electrolyte membrane fuel cells (PEMFC). The multiparameter sensor works with two conventional FBG and achieves an RMSE better than 0.45°C and 4.8 %RH. KW - Proton exchange membrane fuel cells KW - Temperature and humidity KW - Fiber Bragg grating Y1 - 2023 SN - 978-1-957171-30-2 U6 - https://doi.org/10.1364/OFS.2023.Tu3.36 VL - 2023 PB - Optica Publishing Group CY - Washington, D.C. ER - TY - JOUR A1 - Birkner, Lena A1 - Foreta, Michael A1 - Rinaldi, Ali A1 - Orekhov, Anton A1 - Willinger, Marc-Georg A1 - Eichelbaum, Maik T1 - Dynamic accelerated stress test and coupled on-line analysis program to elucidate aging processes in proton exchange membrane fuel cells JF - Scientific Reports N2 - AbstractThe application of hydrogen proton exchange membrane fuel cells (PEMFC) in greenhouse gas emission free heavy-duty vehicles requires extremely durable PEMFC components with service lives in the range of 30,000 h. Hence suitable test and analysis methods are required that reflect realistic operation scenarios, but significantly accelerate aging. For this purpose, a dynamic accelerated stress test was developed, which is coupled with a comprehensive in-depth in-situ and ex-situ analysis program to determine the aging processes of a PEMFC membrane electrode assembly (MEA). The test comprehends dynamic cycling between low, moderate and high load, different temperature and humidity conditions as well as recovery sequences to distinguish between reversible and irreversible failure modes. All phases of the PEMFC system (i.e. solid, liquid and gaseous) are monitored on-line during aging by sophisticated electrochemical, mass spectrometric and ion chromatographic analytical methods. The structural and elemental composition of the MEA before and after the aging program (post-mortem) are investigated by X-ray fluorescence, scanning and transmission electron microscopy. This program was able to age a commercial PEMFC to end-of-life in 1000 h, while providing an accurate picture of the aging processes involved. Y1 - 2024 U6 - https://doi.org/10.1038/s41598-024-54258-8 SN - 2045-2322 VL - 14 IS - 1 PB - Springer Science and Business Media LLC ER - TY - JOUR A1 - Seiß, Volker A1 - Eitel, Dominik A1 - Helbig, Uta A1 - Eichelbaum, Maik T1 - Charge Carrier Dynamics in Undoped and N-Doped Titania Nanolayers upon Ultraviolet and Visible Light Irradiation JF - The Journal of Physical Chemistry C N2 - This paper reports on the successful synthesis of visible light photoactive N–TiO2 nanolayers and the investigation of charge carrier dynamics in dependence on N-doping and irradiation wavelengths. Grazing incidence X-ray diffractometry exhibited that N-doping supports the formation of an anatase phase with a higher crystallinity than observed for undoped TiO2. Photoelectrochemical measurements gave evidence that N–TiO2 is characterized by a significantly higher incident photon conversion efficiency (IPCE) upon both UV and visible light irradiation. Photoelectrochemical impedance spectroscopy revealed that the higher IPCE of N–TiO2 in UV can be explained by a lowered charge transfer resistance, probably due to its higher crystallinity. The higher photoactivity in the visible can be explained by the incorporation of intrabandgap states upon N-doping. This is supported by X-ray photoelectron spectroscopy indicating the incorporation of N atoms in the titania layer, the observed bandgap narrowing by at least 250 meV as measured by ultraviolet–visible absorption spectroscopy, and the decrease of the work function by 50 meV, as derived from scanning Kelvin probe microscopy. Intensity-modulated photocurrent/photovoltage spectroscopy proved that the generally lower quantum yield at visible light is caused not only by the generation of less photoexcited charge carriers, but also by a higher surface hole recombination rate and hence lower hole charge transport efficiency. Y1 - 2024 U6 - https://doi.org/10.1021/acs.jpcc.4c01954 SN - 1932-7447 VL - 128 IS - 28 SP - 11845 EP - 11857 PB - American Chemical Society (ACS) ER - TY - JOUR A1 - Seiß, Volker A1 - Helbig, Uta A1 - Lösel, Ralf A1 - Eichelbaum, Maik T1 - Investigating and correlating photoelectrochemical, photocatalytic, and antimicrobial properties of TiO2 nanolayers JF - Scientific Reports N2 - Semiconducting transition metal oxides such as TiO 2 are promising photo(electro)catalysts for solar water splitting and photoreduction of CO 2 as well as for antibacterial, self-, water and air-cleaning coatings and admixtures in paints, building materials, on window glass or medical devices. In photoelectrocatalytic applications TiO 2 is usually used as photoanode only catalyzing the oxidation reaction. In coatings and admixtures TiO 2 works as heterogeneous catalyst and has to catalyze a complete redox cycle. While photoelectrochemical charge transport parameters are usually quite well accessible by electrochemical measurements, the quantitative description of photocatalytic properties is more challenging. Here, we present a systematic structural, photoelectrocatalytic, photocatalytic and antimicrobial study to understand if and how photoelectrochemical parameters can be used to predict the photocatalytic activity of TiO 2. For this purpose TiO 2 thin films on flourine-doped tin oxide substrates were prepared and annealed at temperatures between 200 and 600 ◦C. The film morphologies and thicknesses were studied by GIXRD, FESEM, and EDX. Photoelectrochemical properties were measured by linear sweep voltammetry, photoelectro-chemical impedance spectroscopy, chopped light chronoamperometry, and intensity modulated photocurrent/photovoltage spectroscopy. For comparison, photocatalytic rate constants were determined by methylene blue degradation and Escherichea coli inactivation and correlated with the deduced photoelectrocatalytic parameters. We found that the respective photoactivities of amorphous and such as charge transfer and recombination rates, charge transfer efficiencies and resistances are measured close to the open circuit potential (OCP). Hence, the interfacial charge transport parameters at the OCP can be indeed used as descriptors for predicting and understanding the photocatalytic activity of TiO 2 coatings. In photoelectro-catalytic applications TiO 2 is usually used as photoanode only catalyzing the oxidation reaction. In coatings and admixtures TiO 2 works as heterogeneous catalyst and has to catalyze a complete redox cycle. While photoelectro-chemical charge transport parameters are usually quite well accessible by electrochemical measurements, the quantitative description of photocatalytic properties is more challenging. Here, we present a systematic structural, photoelectrocatalytic, photocatalytic and antimicrobial study to understand if and how photoelectrochemical parameters can be used to predict the photocatalytic activity of TiO 2. For this purpose TiO 2 thin films on flourine-doped tin oxide substrates were prepared and annealed at temperatures between 200 and 600 Celsius. The film morphologies and thicknesses were studied by GIXRD, FESEM, and EDX. Photoelectrochemical properties were measured by linear sweep voltammetry, photoelectro-chemical impedance spectroscopy, chopped light chronoamperometry, and intensity modulated photocurrent/ photovoltage spectroscopy. For comparison, photocatalytic rate constants were determined by methylene blue degradation and Escherichea coli inactivation and correlated with the deduced photoelectro-catalytic parameters. We found that the respective photoactivities of amorphous and crystalline TiO 2 nanolayers can be best correlated, if the extracted photoelectrochemical parameters such as charge transfer and recombination rates, charge transfer efficiencies and resistances are measured close to the open circuit potential (OCP). Hence, the interfacial charge transport parameters at the OCP can be indeed used as descriptors for predicting and understanding the photocatalytic activity of TiO 2 coatings. Y1 - 2021 U6 - https://doi.org/10.1038/s41598-021-01165-x SN - 2045-2322 VL - 11 IS - 1 PB - Springer Science and Business Media LLC ER - TY - JOUR A1 - Eichelbaum, Maik A1 - Seiß, Volker ED - Eichelbaum, Maik T1 - Analytik photoaktiver Titandioxidschichten BT - Gemeinsamkeiten und Unterschiede zwischen Photokatalyse und Photoelektrochemie JF - GIT Labor-Fachzeitschrift N2 - Spätestens seit den Arbeiten von Fujishima und Honda aus dem Jahr 1972 werden mit UV-Licht bestrahlte Halbleiter wie Titandioxid als Photokatalysator intensiv erforscht und diskutiert. Die Anwendungsbereiche sind dabei äußerst vielfältig. KW - Titandioxid KW - Fotoelektrochemie Y1 - 2022 UR - https://analyticalscience.wiley.com/content/magazine-do/git-labor-fachzeitschrift-03-2022 SN - 0016-3538 VL - 66 IS - März 2022 PB - Wiley ER - TY - JOUR A1 - Eichelbaum, Maik A1 - Seiß, Volker T1 - Analysis of photoactive titanium dioxide layers BT - Common features and differences between photocatalysis and photoelectrochemistry JF - Wiley Analytical Science Magazine N2 - Since the work of Fujishima and Honda in 1972, semiconductors irradiated with UV light, such as titanium dioxide, have been intensively researched and discussed as photocatalysts. The areas of application are highly diverse. KW - Titandioxid KW - Fotoelektrochemie Y1 - 2022 UR - https://analyticalscience.wiley.com/content/magazine-do/wiley-analytical-science-magazine-03-2022 IS - 3 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Eichelbaum, Maik A1 - Thiel, Susanne T1 - Scanning Electrochemical Microscopy BT - Investigation of the Aging of Membrane-Electrode Assemblies JF - Microscopy and Analysis N2 - To extend the lifespan of polymer electrolyte membrane fuel cells and electrolyzers, it is crucial to understand local degeneration processes in membrane electrode assemblies (MEAs). We developed a spatially resolved analytical method that can differentiate between various functional and structural degeneration phenomena during the aging process of a membrane by combining scanning electrochemical microscopy (SECM) with a diffusion flow cell and using hexacyanidoferrate(II) and protons as redox mediators. One SECM scan at a negative potential detects proton diffusion through the membrane, thereby measuring its proton conductivity. A second SECM scan at a positive potential visualizes iron complex diffusion through the membrane, highlighting perforating structural damage, such as cracks and holes. This method has been successfully validated for spatially resolving membrane damage following various aging tests. KW - Rasterelektrochemisches Mikroskop KW - Polymer-Elektrolytmembran-Brennstoffzelle Y1 - 2025 UR - https://analyticalscience.wiley.com/content/magazine-do/microscopy-and-analysis-4-2025 VL - 39 IS - 4 PB - Wiley-VCH ER -