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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]

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]

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]

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]

Zeolites have been found to be promising sensor materials for a variety of gas molecules such as NH3, 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]

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]

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]

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]

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]

The mobility of NH3-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]

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]

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]

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]

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]

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]

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]

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]