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Journal of synchrotron radiation 28(6), 1865 - 1873 (2021). doi:10.1107/S160057752100905X, Vanadium-ion transport through the polymer membrane results in a significant decrease in the capacity of vanadium redox flow batteries. It is assumed that five vanadium species are involved in this process. Micro X-ray absorption near-edge structure spectroscopy (micro-XANES) is a potent method to study chemical reactions during vanadium transport inside the membrane. In this work, protocols for micro-XANES measurements were developed to enable through-plane characterization of the vanadium species in Nafion 117 on beamline P06 of the PETRA III synchrotron radiation facility (DESY, Hamburg, Germany). A Kapton tube diffusion cell with a diameter of 3 mm was constructed. The tube diameter was chosen in order to accommodate laminar flow for cryogenic cooling while allowing easy handling of the cell components by hand. A vertical step size of 2.5 ��m and a horizontal step size of 5 ��m provided sufficient resolution to resolve the profile and good statistics after summing up horizontal rows of scan points. The beam was confined in the horizontal plane to account for the waviness of the membrane. The diffusion of vanadium ions during measurement was inhibited by the cryogenic cooling. Vanadium oxidation, e.g. by water radiolysis (water percentage in the hydrated membrane ���23 wt%), was mitigated by the cryogenic cooling and by minimizing the dwell time per pixel to 5 ms. Thus, the photo-induced oxidation of V$^{3+}$ in the focused beam could be limited to 10%. In diffusion experiments, Nafion inside the diffusion cell was exposed on one side to V$^{3+}$ electrolyte and on the other side to VO$_2$$^{+}$. The ions were allowed to diffuse across the through-plane orientation of the membrane during one of two short defrost times (200 s and 600 s). Subsequent micro-XANES measurements showed the formation of VO$^{2+}$ from V$^{3+}$ and VO$_2$$^{+}$ inside the water body of Nafion. This result proves the suitability of the experimental setup as a powerful tool for the determination of the profile of vanadium species in Nafion and other ionomeric membranes., Published by Wiley-Blackwell, [S.l.]

The influence of process parameters on the H2O2 yield of gas diffusion electrodes (GDE) are investigated. The investigated GDEs consist of Vulcan XC72 carbon black and PTFE on gold‐plated nickel wire cloth. An electrolysis cell is used to evaluate the influence of various process parameters, such as temperature, pH value, oxygen pressure and stoichiometric factor, electrolyte flow regime, current density and separator material at steady‐state conditions. It is found that the investigated GDE enables current efficiencies greater than 90 % at up to 2 kA m−2, whereby lower electrolyte temperatures and higher pH values contribute to higher H2O2 yields above 90 % current efficiency.

To enable the evaluation of water treatment efficiency of electrochemical advanced oxidation processes (EAOPs), an approach to remove H2O2 as a catalytic pretreatment was investigated to av...

The kinetics of zinc dissolution in concentrated potassium hydroxide solution were determined as a function of KOH concentration, amount of added ZnO, and temperature through linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The measurements were evaluated with a simplified reaction scheme in which an intermediate ZnI species is formed on the electrode surface that subsequently reacts to a soluble ZnII species. Analysis of the LSV data with a two-step Butler–Volmer kinetics showed that the transfer coefficients and the surface coverage of the intermediate are approximately constant in the entire range of operation conditions, whereas the exchange current density for the first reaction step is about five times larger than for the second step. Analysis of the dynamic EIS measurements resulted in very similar current densities than obtained from the quasi-stationary LSV method. For the first time, activation energies describing the temperature dependence of the exchange current density were also determined.

Redox flow batteries such as the all-vanadium redox flow battery (VRFB) are a technical solution for storing fluctuating renewable energies on a large scale. The optimization of cells regarding performance, cycle stability as well as cost reduction are the main areas of research which aim to enable more environmentally friendly energy conversion, especially for stationary applications. As a critical component of the electrochemical cell, the membrane influences battery performance, cycle stability, initial investment and maintenance costs. This review provides an overview about flow-battery targeted membranes in the past years (1995–2020). More than 200 membrane samples are sorted into fluoro-carbons, hydro-carbons or N-heterocycles according to the basic polymer used. Furthermore, the common description in membrane technology regarding the membrane structure is applied, whereby the samples are categorized as dense homogeneous, dense heterogeneous, symmetrical or asymmetrically porous. Moreover, these properties as well as the efficiencies achieved from VRFB cycling tests are discussed, e.g., membrane samples of fluoro-carbons, hydro-carbons and N-heterocycles as a function of current density. Membrane properties taken into consideration include membrane thickness, ion-exchange capacity, water uptake and vanadium-ion diffusion. The data on cycle stability and costs of commercial membranes, as well as membrane developments, are compared. Overall, this investigation shows that dense anion-exchange membranes (AEM) and N-heterocycle-based membranes, especially poly(benzimidazole) (PBI) membranes, are suitable for VRFB requiring low self-discharge. Symmetric and asymmetric porous membranes, as well as cation-exchange membranes (CEM) enable VRFB operation at high current densities. Amphoteric ion-exchange membranes (AIEM) and dense heterogeneous CEM are the choice for operation mode with the highest energy efficiency.

Porous glass (PG) offers the ability to vary pore sizes and modify surfaces, allowing membranes to be tailored for a given electrochemical application. In this contribution, the application of PG in all-vanadium redox-flow batteries (VFB) and the effect of surface modification with sulfonic acid groups were investigated, and the results were compared with those from well-known polymeric membranes. The performance of native and surface-modified PG membranes with pore sizes ranging from 2 to 20 nm and thicknesses of 300 and 500 µm was investigated by examining their self-discharge behavior, polarization curves and area resistance. A maximum power density of 77 mW cm−2 at a current density of 110 mA cm−2 was observed with the modified membrane 505FDS, and this density is approximately half the power density achieved with Nafion™ 117. The results can be related to the small vanadium crossover, high conductivity and chemical stability. Therefore, the great potential of PG membranes as separators in VFBs was shown.

Zinc-air batteries have a great potential to be the next generation of secondary batteries. They exhibit a high volume and mass specific power density due to the use of oxygen, which can be taken directly from air. Compared to other anodes used in rechargeable batteries, zinc offers many advantages including low cost and environmental friendliness. Unfortunately, morphological changes occur in the zinc electrode after a few charge and discharge cycles which lead to formation of needle-shaped zinc structures (dendrites). Despite many studies about suppressing dendrites by using additives in the electrolyte, no technically feasible solution could be found until today. In this contribution the influence of zinc ion concentrations in the electrolyte at the electrode surface on the dendrite formation is investigated. It is shown that dendritic zinc crystals only occur if the surface concentration of zinc ions falls below a critical value. With the knowledge of this critical surface concentration the time before growth of dendritic zinc starts can be prolonged by pulsed deposition of zinc. Moreover, dendrite growth can be completely avoided in a flow system at an appropriate flow rate in combination with a pulsed current charging procedure. With this approach the favored boulder structures were obtained with current densities up to 80 mA cm−2 and for deposition times up to 1800 s.

The improvement of redox-flow batteries requires the development of chemically stable and highly conductive separators. Porous glass membranes can be an attractive alternative to the nowadays most common polymeric membranes. Flat porous glass membranes with a pore size in the range from 2 to 50 nm and a thickness of 300 and 500 μm have been used for that purpose. Maximum values for voltage efficiency of 85.1%, coulombic efficiency of 97.9% and energy efficiency of 76.3% at current densities in the range from 20 to 60 mA cm−2 have been achieved. Furthermore, a maximum power density of 95.2 mW cm−2 at a current density of 140 mA cm−2 was gained. These results can be related to small vanadium crossover, high conductivity and chemical stability, confirming the great potential of porous glass membranes for vanadium redox-flow applications.

Electrochemical advanced oxidation processes (EAOP®) are promising technologies for the decentralized treatment of water and will be important elements in achieving a circular economy. To overcome the drawback of the high operational expenses of EAOP® systems, two novel reactors based on a next-generation boron-doped diamond (BDD) anode and a stainless steel cathode or a hydrogen-peroxide-generating gas diffusion electrode (GDE) are presented. This reactor design ensures the long-term stability of BDD anodes. The application potential of the novel reactors is evaluated with artificial wastewater containing phenol (COD of 2000 mg L−1), the reactors are compared to each other and to ozone and peroxone systems. The investigations show that the BDD anode can be optimized for a service life of up to 18 years, reducing the costs for EAOP® significantly. The process comparison shows a degradation efficiency for the BDD–GDE system of up to 135% in comparison to the BDD–stainless steel electrode combination, showing only 75%, 14%, and 8% of the energy consumption of the BDD–stainless steel, ozonation, and peroxonation systems, respectively. Treatment efficiencies of nearly 100% are achieved with both novel electrolysis reactors. Due to the current density adaptation and the GDE integration, which result in energy savings as well as the improvements that significantly extend the lifetime of the BDD electrode, less resources and raw materials are consumed for the power generation and electrode manufacturing processes.

The electron paramagnetic resonance (EPR) spectra of poly (vinylidene fluoride) (PVDF) films were studied in order to identify type and intensity of trapped radicals after an electron treatment with 150 kGy in air at room temperature. The observed EPR spectra consist of superimposed spectra of eight different radicals. The individual spectra were simulated by first derivatives of normalized Gaussian functions including intensity, linewidth, g value, and hyperfine splitting constants of the unpaired electron with hydrogen or fluorine atoms in α or β positions. In addition, the number of trapped radicals was estimated using a standard sample of known spin concentrations. Although initially generated radicals tend to be converted to peroxy radicals in the presence of oxygen, the predominant radical is the CH-based mid-chain radical (–CF2–C*H-CF2-) with a relative intensity of 62.3%. This is attributed to CH-based radicals in the crystalline domains with low molecular mobility leading to an enhancement in its linewidth (ΔHpp ⁓ 3.6 mT). A fraction of 20.7% of all radicals are peroxy radicals with anisotropic g values, g ∥ = 2.0210 and g ⊥ = 2.0095. The relative intensity of allyl, dienyl and polyenyl radicals amounts to 4.9%.

Effective methods for graphite felt (GF) treatment based on Fenton’s reagent treatment and thermal modification have been used to improve microbial fuel cell (MFC) performance. The effects of the H2O2 content in Fenton’s reagent on the performances of MFCs with two different GFs (GFD and ACN-211) have been investigated. For GFD, a maximum performance of 190 mW/m2 was achieved with H2O2 volume of 100 ml, while for ACN-211, the maximum performance of 450 mW/m2 is reached with H2O2 volume of 150 ml. MFCs with both treated and untreated ACN-211 consistently showed higher power densities and greater durabilities than those with treated and untreated GFD. The degree of fouling on the surface of ACN-211 was much less than that on the surface of GFD. The higher surface area and better anti-fouling performance of ACN-211 are responsible for its relatively high power density during long-term operation. Thermal modification of ACN-211 was performed at different temperatures and for different durations, and the effects of treatment conditions on the performances of MFCs were studied. Results showed that an MFC fabricated with ACN-211 treated under 400 °C for 2 h exhibited the highest power density, with a maximum value of 470 mW/m2, which is higher than that of an MFC fabricated with ACN-211 treated by Fenton’s reagent. A Coulombic efficiency of 35% and an energy efficiency of 10% were achieved for an MFC fabricated with ACN-211.

The application of grafted membranes based on modified poly(ethylene-alt-tetrafluoroethylene) (ETFE) in redox flow-batteries is reported. In analogy to commercial Nafion® 117 based membranes ETFE backbone material provides chemical, thermal, and mechanical stability. Side chains composed of 2-hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) grafted to ETFE were sulfonated to achieve the required proton exchange capacity. Application in a vanadium based redox flow-battery demonstrates the applicability of this kind of membranes for energy storage systems. The degree of grafting was identified as the key parameter to tune the membrane properties.

This contribution describes the effect of the quality of the catalyst coating of cathodes for wastewater treatment by microbial fuel cells (MFC). The increase in coating quality led to a strong increase in MFC performance in terms of peak power density and long-term stability. This more uniform coating was realized by an airbrush coating method for applying a self-developed polymeric solution containing different catalysts (MnO2, MoS2, Co3O4). In addition to the possible automation of the presented coating, this method did not require a calcination step. A cathode coated with catalysts, for instance, MnO2/MoS2 (weight ratio 2:1), by airbrush method reached a peak and long-term power density of 320 and 200&ndash, 240 mW/m2, respectively, in a two-chamber MFC. The long-term performance was approximately three times higher than a cathode with the same catalyst system but coated with the former paintbrush method on a smaller cathode surface area. This extraordinary increase in MFC performance confirmed the high impact of catalyst coating quality, which could be stronger than variations in catalyst concentration and composition, as well as in cathode surface area.

A major source of capacity fade of the common vanadium redox flow battery (VRFB) is the vanadium ion transport through the separator. However, different transport models disagree significantly in the diffusion coefficient for the different V species and the influence of different transport mechanisms. The underlying hypothesis of this work is that reactions inside the membrane are partly responsible for these discrepancies. Accordingly, it was investigated if redox reactions inside the nanoscopic water body of Nafion 117 can occur. X-ray absorption near edge structure spectroscopy (XANES) was used to distinguish between the different V species inside hydrated Nafion 117 and novel PVDF-based membranes. It was validated that the speciation of vanadium can be performed using the pre-edge peak energy and intensity. The experiments were performed as follows: strips of the membrane were exposed from one site to a V3+ solution (green) and from the other site to a VO2+ solution (yellow). The ions could diffuse into the membrane from both sides. A change of color of the membrane strip was observed. The blue color in the middle of the strip indicated that VO2+ was formed where V3+ and VO2+ got in contact. Using XANES this reaction inside Nafion was proven.

The mechanical behavior of lithium-ion battery electrodes that undergo a severe capacity decrease are investigated by monitoring the out-of-plane displacement on the external surface of a pouch cell. The capacity degradation does not decrease gradually as a function of time but exhibits distinct behaviors with different causes. These are electrochemical aging during cycling and mechanical injury caused by manufacture failure. In the former case, both the permanent evolution and the anomalous distribution of the displacement accompanied with a consistent decrease of the capacity are correlated to the local deterioration of the adhesion of the material layers. The mechanical injury accelerates the capacity decrease by destroying the electrode structure, which results in a sudden decrease of the surface displacement. If the displacement reaches its limit, only a dynamic fluctuation remains, which reflects the remaining electrochemical process at a low level. As a result, we conclude that the loss of electrical connectivity between the active material layer and the current collector is responsible for the severe capacity degradation. This effect is more pronounced on the anode than the cathode. Both electrochemical cycling and mechanical injury can result in the weakening of the adhesion of the anode material on the current collector.

An electrochemical reactor based on a moving graphite–polymer composite (GPC) cathode and boron-doped diamond anode is developed and used for the electrochemical water softening and treatment of artificial vacuum toilet wastewater. The magnetically actuated cathode is designed for the in situ removal of insoluble compounds, which usually precipitate on the cathode during electrochemical water treatment processes. To obtain a suitable GPC cathode, the chemical stability and conductivity of various composites and their flexion and magnetic actuator characteristics are investigated. The most suitable GPC cathode is a 0.5 mm thick polypropylene-based composite, which presents chemical stability, the lowest resistivity of all analyzed samples (5.06 ± 1.80 mΩ cm), and enables flexions up to 2.4 mm. The water softening performance of the reactor featuring this electrode was evaluated using two configurations. Water hardness was decreased up to 72% and more than 90% in mixed and separated electrolyte modes, respectively. Further investigations demonstrate that this reactor can also be used for wastewater treatment. Artificial toilet wastewater was successfully discolored for reuse as toilet flushing water. Lastly, a treatment test over 120 h demonstrates that the magnetically actuated flexible GPC cathode removes in situ deposits on its surface and requires low maintenance. The performance of the new electrode configuration is similar to that of the state-of-the-art polarity reversal system and does not shorten the electrode service life.

The influence of externally imposed mechanical loading on lithium ion pouch cells is investigated by monitoring the capacity retention and the out-of-plane displacement on the external surface of the cells. Mechanical loading was applied by bending the electrodes prior to electrochemical treatment of the cells. Only the samples loaded with the suitable bending show improved capacity retention. While a large bending diameter leads only to little protection, too small bending diameter results in degradation. The improvements can be attributed to the positive effect of pre-bending on suppression on repeatable volume expansion and thus improve the adhesion of electrode material layers on the current collector. Additionally, an appropriate bending stress may have a protective effect against the formation of deposits on the electrode. The improvement is only effective in an optimal range of the bending diameter (3-10mm). The conclusion can be further proven by electrochemical impedance spectroscopic and the observation on the internal surface area of the electrode.

A continuous process to produce carbon-supported platinum catalysts by polyol reduction was examined. The reactant dispersion was rapidly heated up to reaction temperature while flowing through a directly electrically heated tube followed by a downstream isothermic tubular reactor. Appropriate inner diameters corresponding to the desired short heating-up times were calculated. A certain lower limit for the inner diameter is caused by temporary pluggings of particle agglomerates circumventing steady-state operation. Tube diameters were evaluated with respect to heating-up times and plugging. It was proved that with a tubular reactor a continuous preparation of carbon nanotube-supported platinum catalysts with a low particle size and evenly distributed particles is possible.

A systematic variation of the molar ratio between hydroxide ions and platinum during polyol synthesis of Pt electrocatalysts supported on carbon nanotubes was conducted. The resulting materials were physically characterized by transmission electron microscopy, thermogravimetric analysis, and X-ray diffraction. It could be shown that precise control of the OH−/Pt ratio is necessary for achieving small-sized uniformly distributed Pt nanoparticles at high chemical yield. Simple adjustment of the pH value is not sufficient to control the reduction conditions since even small pH variations give rise to significant changes of the catalyst properties. The optimal OH−/Pt molar ratio was found to be 5:1 resulting in small particle size (ca. 2.5 nm in diameter) and high platinum loading (ca. 39 wt% at a nominal loading of 40 wt%). Moreover, we have shown that the developed electrocatalyst exhibits a high activity toward the oxygen reduction reaction which is confirmed by half-cell experiments in a rotating disk electrode and in single-cell experiments in direct methanol fuel cells.

A setup for optically monitoring the agglomerate growth of multiwalled carbon nanotubes (MWCNTs) by catalytic chemical vapor deposition on single Co–Mn–Al–Mg oxide catalyst particles with ethene as carbon precursor has been developed. Ethene concentrations and temperatures were varied between 5 –75 Vol.% and 550–770 °C, respectively. It could be shown that the agglomerate growth is rapid and the final diameter is reached after a few ten seconds to about 3 min depending on the reaction conditions. The average enlargement factor of the agglomerates over all experiments was found to be 6.5 ± 1.2 compared to the original diameter of the catalyst particle. The growth rate is enhanced by both, reaction temperature and ethene concentration. Hence it is concluded that the agglomerate growth rate is associated with the reaction rate of MWCNT synthesis. Short time experiments and analysis of the resulting agglomerates have confirmed an earlier proposed growth mechanism.

Platinum (Pt) nanoparticles show high activity as catalysts in various chemical reactions. The control of the morphology of Pt nanostructures can provide an opportunity to improve their catalytic properties. The preparation of Pt-loaded iron-oxide polyvinylbenzyl chloride nanocomposites was done in several stages: first by the formation of the core consisting of magnetite nanoparticles and second by the polymerization of vinylbenzyl chloride in the presence of the magnetic core particles. The third step is the amination of the chlorine group with ammonia, which leads to an ion exchange resin. Then, the Pt precursor (H2PtCl6) is attached by ion exchange. Finally, the Pt ions are reduced to Pt metal with NaBH4. The obtained material can be dispersed easily and be used as a catalyst which can be separated after the reaction by magnetic fields. Characterization of the resulting metallic nanocomposites is evaluated by atomic absorption spectroscopy, thermal gravimetric analysis, transmission electron microscopy, infrared spectroscopy, and gas chromatography. The activity of Pt at magnetic core/shell nanocomposites was measured for the reduction reaction of cinnamaldehyde to cinnamyl alcohol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Different types of functionalized polymer magnetic core with diameters of 10-20 nm were prepared by condensation polymerization. Bi-layered polymer magnetic core nanoparticles were prepared by coating of magnetic core hydrophobic polymer shell composites of magnetic polyvinylbenzyl chloride with another layer. The second layer consists of 3-amino-1-propanol, butyl-l, 4-diamine or hexamethylenediamine The morphology and size of the magnetic polymer nanoparticles were characterized by TEM. The structure was characterized by IR, TGA and chemical stability against concentrated hydrochloric acid. The magnetic nanocomposites with hydrophilic behavior were easily separated by magnetic field and gives enhancing for using as nanocarrier in bioapplications.

The improvement of direct methanol fuel cells (DMFCs) requires the development of highly active catalysts. Carbide-derived carbon (CDC) is a new class of carbon materials which are produced via selective extraction of the non-carbon compounds from metal carbides. Nanoporous carbon with a surface area of 906 m2 g−1 and mean pore size of 3.4 nm was produced in consequence of chlorinating pure titanium carbide. This material was oxidatively treated to create the nucleation sites for the metal precursor. An increase of oxygen content in the carbon sample was observed after the functionalization step. The CDC material was subsequently loaded with 18.62 wt.% platinum, with an average particle size of 1.16 nm, by wet impregnation and chemical reduction. As a result, an enhanced electrochemical activity towards oxygen reduction was observed. The maximum power density of 50.16 mW cm−2 was achieved and is subsequently 18% higher than the value measured for commercial platinum catalyst (20 wt.% Pt) on activated carbon. This increase can be attributed to good catalyst dispersion, high surface area and small platinum cluster sizes, thus, confirming the potential of carbide-derived carbon supported catalysts for DMFC applications.

With the rising production of regenerative energy stronger focus on energy storage is necessary. One possibility to store electric energy is the use of battery technology. Especially high energy densities can be realized with metal-air batteries. Zinc-air batteries are known since more than 100 years, but have until now found use only in special markets. A well-known example is the battery for hearing aids. Many attempts have been undertaken to develop rechargeable zinc-based batteries, but only with limited success. Reasons for this fact and directions for future needs, applications and developments are discussed in the paper. Furthermore, first experiments for the use of ionic liquids as electrolytes in zinc-air-batteries are presented.

Polymer magnetic core particles receive growing attention due to these materials owing magnetic properties which are widely used in different applications. The prepared composite particles are characterized with different properties namely: a magnetic core, a hydrophobic first shell, and finally an external second hydrophilic shell. The present study describes a method for the preparation of bi-layered polymer magnetic core particles (diameter range is 50–150 nm). This method comprises several steps including the precipitation of the magnetic iron oxide, coating the magnetite with oleic acid, attaching the first polymer shell by miniemulsion polymerization and finally introducing hydrophilic surface properties by condensation polymerization. The first step is the formation of magnetite nanoparticles within a co-precipitation process using oleic acid as the stabilizing agent for magnetite. The second step is the encapsulation of magnetite into polyvinylbenzyl chloride particles by miniemulsion polymerization to form a magnetic core with a hydrophobic polymer shell. The hydrophobic shell is desired to protect magnetite nanoparticles against chemical attack. The third step is the coating of magnetic core hydrophobic polymer shell composites with a hydrophilic layer of polyethylene glycol by condensation polymerization. Regarding the miniemulsion polymerization the influence of the amount of water, the mixing intensity and the surfactant concentration were studied with respect to the formation of particles which can be further used in chemical engineering applications. The resulting magnetic polymer nanoparticles were characterized by particle size measurement, chemical stability, iron content, TEM, SEM, and IR.

Platinum electrocatalysts deposited on multi-walled carbon nanotubes (CNT) with high loading were prepared using a microwave-assisted polyol reduction method and employed for direct methanol fuel cells (DMFC). A zwitterionic surfactant was used as a stabilizing agent for the formation of Pt nanoparticles. A uniform and narrow size distribution of highly dispersed Pt nanoparticles could be achieved by adjusting the weight ratio of surfactant to Pt precursor allowing for Pt loadings of up to 60 wt%. The heating time and the temperature for the ethylene glycol (EG) oxidation were found to be the key factors for depositing Pt nanoparticles homogeneously on carbon nanotubes. The smallest average particle diameter of 1.8 nm was obtained through microwave heating to 140 °C in 50 s. The structure, amount and morphology of the electrocatalysts were characterized with XRD, TGA, and TEM, respectively. Single cell DMFC measurements were performed in a membrane-electrode assembly (MEA) with 5 cm2 active area and very low catalyst loading (0.25 mg cm−2 of noble metal on both anode and cathode). The DMFC performance of the surfactant stabilized cathode catalyst obtained by the new method described here revealed that the power density was three times higher than for a commercial catalyst used for comparison and two times higher than for an unstabilized CNT supported catalyst.

Im Rahmen des Projekts μ-Consortium wurde eine mobile Praktikumsanlage zur Einbindung der Mikroverfahrenstechnik in die Lehre realisiert. Zur Vermittlung von Kenntnissen in einer Vielzahl verfahrenstechnischer Operationen im Mikromasstab wurden Praktikumsversuche zu den Themengebieten Mischen und homogene Reaktion, heterogene Reaktionen, Warmeubertragung und Partikelsynthese entwickelt.

Due to increasingly stringent environmental regulations for dealing with production residues, the purification of persistent residues have moved into research focus. Therefore, the inner recycling of process waters as a secondary raw material is getting continuously more relevant. In search for new and efficient methods to purify process waters, electrochemical processes have moved to an aspiringly research emphasis. Especially electrochemical oxidation process are receiving much attention, in which strong oxidants are generated in situ, either directly on the electrode surfaces or indirectly, for instance through chemical trace substances (hypochlorite for example). An innovative concept for removing trace elements is a combination of a boron-doped diamond electrode and a gas diffusion electrode (GDE) for generating highly oxidative species at both electrodes simultaneously. Such a system is not commercial available yet, which is mainly due to the absence of high efficient hydrogen peroxide generating gas diffusion electrodes working at greater current densities. In addition to the challenging technical GDE design, the operating parameters strongly affect the electrochemical performance of H2O2-GDEs. While many published articles are screening electrodes under untechnical aspects with small Rotating-Ring-Disc-Electrode Systems [1, 2] or potential-controlled small scale electrolyzers [3, 4, 5], more technical-relevant scales under technical galvanostatic operation are missing. Therefore, a technical-relevant scale of laboratory electrolysis with 100 square centimeters respectively was used, to evaluate the influence of process parameters to determine optimized operating points. The impact of current density, electrolytes pH-value, temperature (first results on the H2O2 concentration depending on temperature using 1 molar sodium hydroxide solution for a current density of 0.5 kA/m2 are presented in the diagram below) and O2 volume flow rate and the effect of the difference pressure were measured with respect to the H2O2-yield. Finally, optimum process conditions for H2O2-producing GDE-evaluation are suggested. References J. F. Carneiro, R. S. Rocha, P. Hammer, R. Bertazzoli and M.R.V. Lanza, Applied Catalysis A: General, 517, 161–167 (2016). W. R.P. Barros, R. M. Reis, R. S. Rocha and M. R.V. Lanza, Electrochimica Acta, 104, 12–18 (2013). H. Luo, C. Li, C. Wu and X. Dong, RSC Adv, 5(80), 65227–65235 (2015). R. S. Rocha, R. M. Reis, Beati, André A. G. F., M. R. V. Lanza, Sotomayor, Maria Del Pilar T. and R. Bertazzoli, Quím. Nova, 35(10), 1961–1966 (2012). M. Panizza and G. Cerisola, Electrochimica Acta, 54(2), 876–878 (2008). Figure 1

Magnetic composite particles with a magnetic core consisting of superparamagnetic iron oxide and a cover layer of hydrophobic polyvinylbenzylchloride are described. The magnetite was prepared by precipitation starting with mixed iron II and iron III salts and coating of the solid with oleic acid. The coating is conducted via the liquid–liquid phase transfer. Thereby oleic acid adsorbed on the magnetite surface. In a second step the oleic acid treated magnetite was coated with polyvinylbenzylchloride in a miniemulsion polymerization to get a protective layer. The obtained magnetite core-shell nano-composites with chlorine functionality were characterized by different methods: particle size measurement, acid treatment, iron content, morphology and elemental profiles across the composite particles diameter. The test result reveals the binding of the iron oxide inside the composites which can be also recognize in TEM pictures.

Cobalt-based monolithic and powder catalysts for Fischer−Tropsch synthesis were prepared. The alumina-supported catalysts contained cobalt (18.6 ± 0.9 wt %) and rhenium (1.2 ± 0.1 wt %) as active phases. To ensure the comparability of both catalysts, monolithic and powder catalysts were prepared from the same CoRe/γ-Al2O3 active powder. While the monolith was prepared by dip coating, the slurry for the coating procedure was also used for preparation of the powder catalyst. It could be shown that both catalysts have comparable composition, pore structure, Brunauer−Emmett−Teller (BET) surface area, and active metal surface area. Catalytic measurements with suspended powder catalyst in a stirred tank reactor and monolithic catalyst in a fixed-bed reactor in the slug-flow regime were performed during Fischer−Tropsch synthesis. Higher reaction rates at comparable methane selectivities were obtained with the monolithic catalyst. Estimations show that the advantageous mass-transfer characteristics of the monolit...

Es wurden optische Messmethoden hinsichtlich ihrer Eignung zur Charakterisierung von mikromechanischen Bauelementen bewertet. Ein weiterer Schwerpunkt war das Langzeitmonitoring von Materialeigenschaften mittels optischer Messtechniken. Dies wurde am Beispiel von HF-MEMS-Schaltern untersucht.

At our institutes composite materials were developed, which ideally allow to combine polymer functionalization utilized for organic synthesis with good mass transfer properties of monolithic carriers. Starting with a megaporous glass carrier material, a polymer is introduced into the pore volume of this support. During the precipitation co-polymerization small polymer spheres are formed, which are connected by polymer bridges, resulting in a rigid polymer monolith intruding the glass. This unique combination leads to versatile materials for organic synthesis, which can be used in a flow-through mode. Based on these monolithic materials with different polymer functionalities a wide variety of different chemical reactions was conducted such as selective reductions, Suzuki cross coupling reactions, nucleophilic substitutions and catalytic transfer hydrogenations. These reactions were performed with reactors constructed from monolithic materials of different sizes allowing to achieve production capacities ranging from the millimole range to several gramms.

The introduction of continuous-flow techniques in the field of solid-phase assisted organic synthesis requires appropriate reactors. These flow reactors must fulfill several requirements, ranging from aspects of chemical reaction engineering and cost-effective manufacturing to specific conditions in organic synthetic methods. The successful manufacturing of such flow reactors requires the interdisciplinary cooperation of different research teams, complementing each other. In this paper, the development of the PASSflow reactor is described, which covers aspects of mechanical reactor design based on chemical reaction engineering concepts. In addition, the utilization of these optimized reactors in palladium(0)-catalyzed Suzuki−Miyaura cross-coupling reactions is presented.

To get information for the development of a continuous MEA fabrication sequence various preparation strategies are investigated. Diffusion layer suspension is made by magnetic stirring, ultrasound mixing and by use of a ball-mill and the slurry is characterised by particle size measurements. The catalytic layers are applied either to the diffusion backing or directly onto the membrane. The latter method yields to improved MEA performance due to the higher utilisation of the catalytic material. Experiments concerning the influence of the anodic diffusion layer thickness and composition show a strong influence on MEA characteristic. For the anodic diffusion layer the influence of the hydrophobicity on methanol transport and CO2 removal is investigated by using PTFE or Nafion© as binder. The Nafion© bonded backing shows better mass transport properties for methanol but CO2 removal becomes crucial at high current densities. Sintering of the PTFE bonded structure improves layer properties for the management of liquid and gas transport. Best results are achieved with sintered PTFE bonded layers with a reduced layer thickness.

Reforming of diesel fuel is challenging but very attractive for hydrogen production. It can facilitate the market entrance of fuel cells due to the existing infrastructure for distribution of diesel fuel. Reforming in micro reactors enables good heat transfer and therefore small and compact fuel processing systems e.g. for electrical energy generation in auxiliary power units.Due to the complexity of diesel, reforming of different diesel components and conversion intermediates in a micro reactor is investigated systematically within this work. Methane and propane were applied as conversion intermediates and hexadecane as a diesel surrogate. All experiments were conducted over a rhodium catalyst on Al2O3 or CeO2.For evaporation of the higher boiling hydrocarbons a micro structured injection nozzle was fabricated to create a fine hydrocarbon spray which evaporates in water vapour. Furthermore a complex gas chromatographic method to analyse hydrocarbons up to C16 and the permanent gases in one analysis run was developed.Experimental results show that the turnover frequency of the fuel molecules in the feed decreases linearly for straight chain hydrocarbons with an increasing number of carbon atoms. Calculations show that the observed conversions and product gas compositions are close to the thermodynamic equilibrium. The catalyst system Rh/CeO2 offers better reforming performance and higher resistance to coking apparently due to less acidic sites compared to Al2O3 and the oxygen storage capacity of CeO2.The ongoing work will examine the reforming behaviour of more model diesel fuel components e.g. mixtures of hexadecane and methylnaphthalene or synthetic diesel fuel. Experiments will be conducted in an optimised micro reformer, which disposes the heating energy by burning e.g. fuel cell off-gases. This also offers the consideration of start up and load changing behaviour.

A chemistapos;s wish finally becomes reality: microreactors for every synthetic laboratory! By precipitation polymerization various polymers are introduced into the irregular pore system of a porous glass rod. By embedding these rods into a housing, followed by functionalization and immobilization of reagents onto the polymer phase, versatile microreactors are obtained. With this apparatus, chemical transformations in solution can be performed, for example, a steroid derivatization.

For optimizing lead-structures that evolve from high-throughput parallel synthesis (combinatorial chemistry) in increasing numbers of tools for automated synthesis in millimolar scale becomes necessary. For this purpose, the combination of solution phase and solid phase synthesis would be ideal. This can be achieved by immobilizing reagents and catalysts on a polymer support. By fixing one of the reactants on such a support the starting material and product stay in solution. Applied to a flow through system, the product leaves the reactor in solution. For this purpose we developed a new microreactor.