Analysis Of Impedance Data Research Articles

Electrical transport properties of PFO: MEH-PPV polymer blends

Present study investigates the electrical properties of a thin film of poly(9,9-dihexyl fluorenyl-2,7-diyl): poly(2-methoxy-5-(2-ethylhexyloxy)-1, 4-phynylenevinylene) (PFO:MEHPPV) polymer blends using impedance spectroscopy in the frequency range of 0.1 Hz–1 MHz. From the analysis of complex impedance data, we found that in the PFO: MEH-PPV polymer blend structure, the best way to describe the conductivity is a single relaxation process. An improved conductivity of the blended PFO polymer thin film was obtained on the basis of different concentrations of MEH-PPV. Cole-Cole plots for blend devices are characterized with a single network of parallel combination of resistor RP and capacitor CP with series resistance RS. The resistance RP decreases when a bias is applied, however the capacitance CP does not change substantially.

Crystal structure, electric and microwave dielectric properties of La2Mg(Mg1/3Sb2/3)O6 novel double-perovskite with non-stoichiometric 1:1 cationic ordering

In this contribution, the novel double-perovskite La2Mg(Mg1/3Sb2/3)O6 has been successfully prepared by solid-state reaction method, and its structure has been determined for the first time by a combination of X-ray and neutron powder diffraction data analysis. The novel material exhibits a thermal expansion of ∼9.1 ppm/°C and a large optical band gap (4.23 eV). The complex impedance data analysis indicates that La2Mg(Mg1/3Sb2/3)O6 features a Debye-like behaviour, with a bulk conductivity, σb, varying between 10-7-10-4 S ‧cm-1 within 500–900 °C temperature range, and activation energy (Ea) of ∼ 1.36 eV. In addition, the microwave dielectric properties of La2Mg(Mg1/3Sb2/3)O6 sintered at 1625 °C display optimized quality factor (Q×f) of ∼ 28,700 GHz (f = 9.65 GHz), a dielectric constant (εr) of ∼ 20.2 and temperature coefficient of the resonant frequency (τf) of ∼ − 89 ppm/°C. This work widen the reduced number of A3+B2/32+B1/35+O3 compounds explored so far.

Impedance analysis of electrolyte-supported solid oxide fuel cell with nickel-tungsten-cerium anode fed with CH4-CO2 mixtures and siloxanes

An electrolyte-supported solid oxide fuel cell with WNi-Ce as anode has been tested with direct feed of simulated biogas mixtures. Three gas compositions have been tested with CH4/CO2 ratio =1.1, 1.7 and 2.8. Testing was carried out during 130 h under a load demand of 100 mA cm−2 at 750 °C, followed by adding 1 ppm of D4 siloxanes to biogas rich in methane on the cell performance, and operation under the same conditions during 180 h. The electrochemical behaviour of the cell has been evaluated by IV curves, electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT). No degradation was detected in the three biogas compositions studied, although the cell performance improved in biogas rich in CH4. However, the presence of siloxanes in biogas caused a progressive performance degradation. EIS measurements and the corresponding DRT analysis presented six or seven peaks which allow identify different physical and chemical processes that take place in the cell. In addition, impedance data analysis revealed that the cell degradation in biogas with siloxanes is mainly caused by an important increase in the polarization resistance attributed to biogas reforming and fuel conversion processes. Post-mortem analysis of the anode surface with SEM and XPS shows microstructural changes and the presence of silicon and traces of carbon species.

(Invited, Digital Presentation) Impedance Analysis of Porous Electrodes in Solid Oxide and Polymer Electrolyte Fuel Cells

Technical electrodes in fuel cells rely on complex multiphase microstructures that facilitate electronic, ionic and gas transport to active reaction sites distributed in the electrode volume. In such electrodes, material and microstructural properties of the porous electrode likewise determine the cell performance and different losses related to gas diffusion, electronic / ionic transport or the charge transfer at the active reaction sites might dominate the electrode resistance.Impedance spectroscopy is a powerful tool to evaluate and quantify the losses within a porous electrode. In this contribution it will be shown how impedance spectroscopy, an impedance data analysis by the distribution of relaxation times (DRT) (1,2) and a subsequent transmission line modeling (TLM) can provide physicochemically meaningful information about technical electrodes applied in solid oxide cells (SOC) (3-7) and polymer electrolyte fuel cells (PEFC) (4,5). Limitations in TLM will be discussed and it will be shown that the well-established straight-forward approach of CNLS-fitting might lead to physicochemically incorrect results. Possible countermeasures as a pre-identification of TLM-parameters by means of separate electrical measurements and microstructural analysis or an appropriate selection of operating parameters during impedance analysis will be presented.An example for the application of TLM in electrode development and microstructural design of the multiphase microstructure will be discussed and examples how the TLM-approach can be used to optimize an electrode in consideration of available materials and producible microstructures will be shown.(1) S. Dierickx, A. Weber and E. Ivers-Tiffée, Electrochim Acta, 355, p. 136764 (2020).(2) A. Weber, tm - Technisches Messen, 88 (1), p. 1 (2021).(3) C. Endler-Schuck, J. Joos, C. Niedrig, A. Weber and E. Ivers-Tiffée, Solid State Ionics, 269, p. 67 (2015).(4) M. Heinzmann, A. Weber and E. Ivers-Tiffée, J. Power Sources, 402, p. 24 (2018).(5) M. Heinzmann, A. Weber and E. Ivers-Tiffée, J. Power Sources, 444, p. 227279 (2019).(6) S. Dierickx, J. Joos, A. Weber and E. Ivers-Tiffée, Electrochim Acta, 265, p. 736 (2018).(7) S. Dierickx, T. Mundloch, A. Weber and E. Ivers-Tiffée, J. Power Sources, 415, p. 69 (2019).

Spatially Resolved Deconvolution of Loss Processes in PEM Fuel Cells

The complex operating behaviour of PEM Fuel Cells is heavily influenced by different non-linear loss processes, which limit the cell performance. Depending on the operating conditions, the different losses change in magnitude and characteristic time constants [1]. During technical operation of large-sized PEM Fuel Cells, gradients in operating conditions occur along the gas channels, resulting in an inhomogeneous current density distribution. This is caused by the locally varying electrochemical activity due to in-plane gradients in concentrations of reactants and reaction products, gas pressure and temperature. Consequently, each loss process occurs locally distributed to a varying degree. Therefore, a profound knowledge about the spatial distribution of losses is essential for optimizing the operating strategy as well as the cell and stack components.The commonly measured I/V characteristics provide only integral information about the overall performance. Thus, the data obtained represent merely the sum of all loss processes averaged over the entire cell area and do not allow detailed conclusions about the respective spatial distribution along the channel.Inevitably, in order to deconvolute the loss processes in the entire area of large sized cells, an approach is required that provides deeper insight in the processes and their interdependencies. For this purpose, an impedance-based methodology is developed that enables a spatially resolved deconvolution of loss processes. It is based on electrochemical impedance spectroscopy (EIS) and an impedance data analysis by the distribution of relaxation times (DRT) [2,3] that is applied to a segmented cell [4] with almost gradient-free segments. By systematically varying operating conditions the different loss processes are identified, quantified and separated with respect to their characteristic frequencies.In this contribution the design of the test bench and the segmented cell will be presented. Furthermore, first results regarding the electrochemical characterization and the impedance-based deconvolution of loss processes in a segmented cell will be discussed. M. Heinzmann et al., J. Power Sources 402, pp. 24-33 (2018).H. Schichlein et al., J. Appl. Electrochem. 32, pp. 875-882 (2002).E. Ivers-Tiffée et al., J. Ceram. Soc. Japan 125, pp. 193-201 (2017).T. Reshetenko et al., J. Electrochem. Soc. 163, pp. F1100-F1106 (2016)

Influence of Three-Dimensional Flow Field Structures Consisting of Expanded Metal Meshes on the Physicochemical Loss Processes in Pemfcs

To further increase the performance of polymer electrolyte membrane fuel cells (PEMFCs) at high current densities, a reduction of mass transport losses by an enhanced evacuation of water from the cell and an improved supply of gases to the reactive sites are necessary.The application of three-dimensional flow field structures in PEMFCs is a promising measure to promote the evacuation of excess liquid water from the cell while boosting the transport of reactants from the gas channel in the direction of the cell. Expanded metal meshes offer a three-dimensional geometry, which predestines them to be used as flow field structures in PEMFCs. In the past, their application as flow fields has primarily been investigated for direct methanol fuel cells (DMFCs) [1, 2, 3] and electrolyzers [4, 5]. To gain a profound understanding of the impact of such three-dimensional flow field structures on the electrochemical properties of PEMFCs, the physicochemical loss processes of the cell have to be analyzed in detail.In this contribution, the results of an in-depth analysis of the influence of three-dimensional flow field structures consisting of expanded metal meshes on the physicochemical loss processes in PEMFCs and their effect on the cell performance is presented. To assess the impact of expanded metal meshes in comparison to a conventional channel rib flow field design, the physicochemical loss processes were examined for both flow field designs. The operating conditions (j, RH, T, pO2) of the incremental PEM fuel cells (1 cm2 active cell area) [6] were varied systematically and the cells were analyzed by means of polarization curves and electrochemical impedance spectroscopy (EIS). The physicochemical loss processes of the cells were identified by a subsequent impedance data analysis by the distribution of relaxation times (DRT) [7, 8].This investigation aims to determine the physicochemical loss process in PEMFCs with expanded metal meshes as flow field structures and compare them to the results of a conventional flow field design. Based on the physical interpretation of the results, consequences and conclusions for the further development of the expanded metal flow field geometries are discussed.

Ni-Ce-ZrO2 system as anode material for direct internal reforming biogas solid oxide fuel cells

This paper is focused on the synthesis of ceria-doped Ni-ZrO2 nanocrystals (Ni-CZ) via a novel synthetic strategy based on wet impregnation and its application as anode material for solid oxide fuel cell (SOFC) directly fuelled by biogas. The electrochemical behaviour of Ni-CZ was evaluated by means of IV curves and impedance spectroscopy in H2 and simulated biogas at 750–850 °C using yttria stabilized zirconia (YSZ) electrolyte-supported cell. The cell achieved higher power density in H2 and at higher temperature. The distribution of relaxation time (DRT) analysis of impedance data was carried to determine the contribution of electrodes processes. Detailed of electrochemical analysis revealed that the cell performance limiting factor corresponds to the electrodes processes at low frequencies which are related to gas diffusion in H2 and dry reforming process and water-gas shit reaction coupled to gas diffusion in biogas. The cell showed a stable performance or even better activation in biogas under aggressive operation condition (400 mV) that could favour its degradation at 750 °C and 800 °C for 20 h and at 850 °C for 200 h. Furthermore post-tests analysis detected negligible carbon deposition on the anode surface. Although Ni-CZ could be postulated as SOFC anode material for direct biogas due to its good stability, an improvement its electrochemical perform is required.

Guidelines to correctly measure the lithium ion conductivity of oxide ceramic electrolytes based on a harmonized testing procedure

Ionic conductivities of Li-ion conducting ceramic electrolytes, mostly evaluated by means of impedance spectroscopy, are a key parameter decisive for their application. Nevertheless, significant deviations in the ionic conductivity of nominally identical samples are reported in literature, which are attributed to material and sample preparation as well as measurement related differences. The goal of this study is a detailed assessment of impedance measurement deviations of 10 identically prepared samples of each Li6.45La3Zr1.6Ta0.4Al0.05O12 (LLZO:Ta:Al) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), respectively. By introducing a harmonized testing procedure for impedance measurement and data analysis, deviations among the participating labs were reduced to differences <1.8% for LLZO and <3.1% for LATP. A complete assessment of instrumentation (fitting, temperature and impedance measurement errors) and sample geometry related errors revealed a high measurement precision with a total error <1.1%. Further on a decreasing ionic conductivity was observed for both materials during the study. Indications for testing and storage induced aging mechanisms were obtained by additional measurements.

Two-methods approach to follow up biomass by impedance spectroscopy: Bacillus thuringiensis fermentations as a study model.

Impedance spectroscopy is used for the characterization of electrochemical systems as well as for the monitoring of bioprocesses. However, the data obtained using this technique allow multiple interpretations, depending on the methodology implemented. Hence, it is necessary to establish a robust methodology to reliably follow-up biomass in fermentations. In the present work, two methodological approaches, mainly used for the characterization of electrochemical systems, were employed to characterize and determine a frequency that allows the monitoring of biomass in Bacillus thuringiensis fermentations by impedance spectroscopy. The first approach, based on a conventional analysis, revealed a single distribution with a characteristic frequency of around 2kHz. In contrast, the second approach, based on the distribution of relaxation times, gave three distributions (A, B, and C). The C distribution, found near 9kHz, was more related to the microbial biomass than the distribution at 2kHz using the equivalent circuits. The time course of the B. thuringiensis fermentation was followed; bacilli, spores, glucose, and acid and base consumption for pH were determined out of line; and capacitance at 9kHz was monitored. The correlation between the time course data and the capacitance profile indicated that the monitoring of B. thuringiensis at 9kHz mainly corresponds to extracellular activity and, in a second instance, to the cellular concentration. These results show that it is necessary to establish a robust and reliable methodology to monitor fermentation processes by impedance spectroscopy, and the distribution of relaxation times was more appropriate. KEY POINTS: • Application of impedance spectroscopy for bioprocess monitoring • Low-frequency monitoring of biomass in fermentations • Analysis of impedance data by two methodological approaches.

High performance silicon electrode enabled by titanicone coating

This paper presents the electrochemical performance and characterization of nano Si electrodes coated with titanicone (TiGL) as an anode for Li ion batteries (LIBs). Atomic layer deposition (ALD) of the metal combined with the molecular layer deposition (MLD) of the organic precursor is used to prepare coated electrodes at different temperatures with improved performance compared to the uncoated Si electrode. Coated electrodes prepared at 150 °C deliver the highest capacity and best current response of 1800 mAh g−1 at 0.1 C and 150 mAh g−1 at 20 C. This represented a substantial improvement compared to the Si baseline which delivers a capacity of 1100 mAh g−1 at 0.1 C but fails to deliver capacity at 20 C. Moreover, the optimized coated electrode shows an outstanding capacity of 1200 mAh g−1 at 1 C for 350 cycles with a capacity retention of 93%. The improved discharge capacity, electrode efficiencies, rate capability and electrochemical stability for the Si-based electrode presented in this manuscript are directly correlated to the optimized TiGL coating layer deposited by the ALD/MLD processes, which enhances lithium kinetics and electronic conductivity as demonstrated by equivalent circuit analysis of low frequency impedance data and conductivity measurements. The coating strategy also stabilizes SEI film formation with better Coulombic efficiencies (CE) and improves long cycling stability by reducing capacity lost.

Staging Breast Cancer-Related Lymphedema with Bioimpedance Spectroscopy.

Background: A number of different classification schemes, with generally similar but not identical criteria, exist to describe the different stages of lymphedema. Criteria may include both subjective and objective assessments. The present study investigated whether bioelectrical impedance parameters had utility in staging breast cancer-related lymphedema. Methods and Results: Hierarchical agglomerative cluster analysis was used to assign women (n = 221) at risk of or with clinically ascribed lymphedema to clusters sharing similar impedance characteristics. Five clusters could be identified with each cluster containing proportions of participants that closely aligned with staging allocation, according to International Society of Lymphology criteria, at initial presentation. The use of cluster analysis for tracking of lymphedema progression or response to treatment is demonstrated. Conclusions: No single assessment provides definitive assignment of a patient to lymphedema stage. Staging is usually achieved by identifying and allocating a patient to a lymphedema stage shared by a group of patients with similar clinical signs. Cluster analysis of impedance data provides similar groupings of patients and could provide a useful adjunct objective assessment for staging lymphedema.

Frequency-Time Domain (FTD) Impedance Data Analysis to Improve Accuracy of Microparticle Enumeration in a Microfluidic Electronic Counter.

Experimental background noise present in biosensors' data hinders the ability for sensitive and accurate detection of critical biomarkers. Here, we report our digital signal processing analysis with respect to frequency and time domain (FTD) data to reduce noise in an experimental microfluidic impedance cytometer. We evaluated the effectiveness of employed noise filtering techniques independently, including baseline drift correction, high frequency noise filtering, and powerline interference mitigation. We further explored the combined effect of all filters and determine improvements in signal-to-noise (SNR) ratio and particle counting accuracy. By removing noise regimes, SNR improved with this impedance cytometer device, and our future efforts will explore filtering effects of more specific and uncommon noise spectrums to greater optimize device performance.

Dopant induced anomalous field dependent mobility behavior of poly(3-octylthiophene) devices

Temperature dependent DC current-voltage (I-V) down to 50 K and field-dependent AC impedance measurements were carried out to study the electric field and temperature dependence of charge carrier mobility in Poly(3-octylthiophene) based metal/polymer/metal device structures of different charge carrier concentrations. In highly doped device, a negative field-dependent mobility (NFDM) which vanishes below 150 K was observed whereas a positive field-dependent mobility (PFDM) was observed in moderately doped devices. The observed NFDM is attributed to the low energetic disorder and high positional disorder in the highly doped devices. With further lowering of carrier concentration, charge carrier mobility first decreases with the increase in applied field attaining a minimum value and then increases with the applied field. At higher temperatures (T>150K), all the three devices show thermally-activated process and activation energy increases with lowering the charge carrier concentrations indicating that doping level plays important role in thermally activated transport mechanism. However, in lower temperature (T<100K), activation energy is almost independent of doping level suggesting that injected carrier plays an important role in the lower temperature region. Data from AC impedance measurement also supports the field-dependent mobility model of conduction mechanism in the devices. Analysis of the AC impedance data of the three devices reveals that the equivalent circuit of highly and moderately doped devices is different from that of the low carrier concentration device. The presence of highly energetic disorder in low carrier concentration devices is also confirmed from AC impedance analysis.

Investigation of La2-XSrxNi0.8Co0.2O4+d (0.0 ≤ x ≤ 0.2) Materials as Oxygen Electrodes for Solid Oxide Cells

Lanthanide Nickelate Ln2NiO4+δ (Ln = La, Pr or Nd) has drawn significant attention as an oxygen electrode for solid oxide cells (SOCs) due to its mixed ionic and electronic conductivity (MIEC) property. They exhibit very good electro-catalytic activity as well as high oxygen diffusion coefficient (D*) and surface exchange coefficient (k*) values [1]. Earlier reported results [2, 3] show that the partial substitution of Co2+ at B-site in La2Ni1−xCoxO4+δ (LNCO) lead to an enhancement in the transport and electrochemical properties of the material. The present study aims to investigate the effect of Sr2+ substitution at A-site in LNCO i.e. La2-xSrxNi0.8Co0.2O4+δ (LSNCO) in order to further investigate the structural, physico-chemical and electrochemical properties of the materials. Three different compositions i.e. LSNCO5, LSNCO10 and LSNCO20 were studied with x = 0.05, 0.10 and 0.20 respectively. First the materials were characterized by XRD, TGA and SEM. Then, the electrochemical characterizations were carried out by fabricating the symmetrical half-cells (8YSZ//GDC//LSNCO) as well as single cells (NiO-YSZ//8YSZ//GDC//LSNCO) using Electrochemical Impedance Spectroscopy (EIS) in 700 – 900 °C temperature range.All these materials exist with orthorhombic structure and a decrease in the cell volume as well as oxygen content (4+δ) is observed with Sr-substitution. The TGA analyses as a function of temperature reveals that these materials show reversible oxygen exchange and are always over-stoichiometric in 25-1000 °C temperature range. However, the loss of oxygen with increasing temperature is decreased with increasing Sr-content. The EIS data analysis of the symmetrical half-cells shows an increase in polarization resistance (Rp) with increasing the Sr-content. For instance, the Rp values of 0.047 and 0.88 Ω.cm2 are observed for LSNCO5 and LSNC20 respectively at 800 °C under air at OCV conditions. The EIS measurements under different partial pressure of oxygen reveals that four electrode processes (as fitted by 4R//CPE along with a series resistance Rs) are involved in the oxygen reduction/evolution mechanism. The observed electrode processes are; ionic transfer of oxide ion through electrode electrolyte interface (R1), charge transfer process (R2), adsorption/desorption of atomic species (R3) and molecular gas diffusion process (R4). The impedance data analysis under polarization (-0.2 to +0.2 V) reveals a decrease in the exchange current density with the increase of Sr-content. For instance, the io value is 0.040 A.cm-2 for LSNCO5 which is decreased to 0.003 A.cm-2 for LSNCO20 at 800 °C. Current-Voltage characteristics obtained from the single cell measurements show a decrease in the current density with increasing Sr-content.The detailed structural, physico-chemical and electrochemical properties of these materials will be presented and discuss in detail.

Deconvolution of Gas Diffusion Polarization in Ni/Gadolinium-Doped Ceria Fuel Electrodes

Electrochemical impedance spectroscopy and the subsequent impedance data analysis by the distribution of relaxation times (DRT) represent a powerful method to unfold electrochemical processes in solid oxide cells. This approach has been successfully demonstrated for electrolyte [1, 2] as well as anode-supported [3] solid oxide cells exhibiting a nickel / yttria-stabilized zirconia (Ni/YSZ) fuel electrode. Applying this methodology, all physicochemical loss processes occurring in the cells could be identified by their relaxation frequencies and subsequently quantified by means of CNLS-fitting.However, in the case of cells exhibiting a Ni/Gadolinium-doped ceria (Ni/CGO) fuel electrode, an unambiguous process assignment in the DRT has not been feasible up to now, since the charge transfer and gas diffusion overlap in the spectrum [4, 5]. The latter is caused by the oxygen non-stoichiometry of CGO, which results in a large chemical capacity, shifting the relaxation frequency of the charge transfer process towards lower relaxation frequencies. The resulting overlap of charge transfer and gas diffusion process in the spectrum impedes a direct deconvolution of these two processes [6].Facing this challenge, we here present a solution of isolating and quantifying the gas diffusion process at the fuel electrode with the help of ternary fuel mixtures exhibiting different gas diffusion coefficients. The gas diffusion coefficients of hydrogen and steam were altered by changing the inert gas component between nitrogen and helium respectively. As the two gas mixtures exhibit identical reactant and reaction product concentrations, the charge transfer polarization is not affected. The differences in polarization resistance R pol, which become visible in figure 1, are solely caused by the differences in gas diffusion polarization [2].In this contribution the detailed procedure to quantify the gas diffusion polarization and an effective gas transport parameter predicting the gas diffusion resistance for arbitrary fuel mixtures are introduced. Furthermore, the applicability of this approach for the parameterization of a zero-dimensional cell model [3] for a solid oxide cell with Ni/CGO fuel electrode will be presented.

Exploring the Role of Humidity, Temperature, and Mixed Ionic and Electronic Conductivity on SOFC Anode Electrocatalysis

Infiltration of nanoscale electrocatalysts into Ni/yttria-stabilized zirconia (Ni-YSZ) cermets has been shown to improve the electrochemical performance of solid oxide fuel cell (SOFC) anodes. While infiltrated electrodes in SOFCs result in improved cell performance, long-term operation leads to coarsening of the infiltrated nanoparticles and negates the short-term performance improvements. This study explores the roles of humidity, temperature, and number of cycles of nanocatalyst infiltration in improving mixed conduction within the Ni-YSZ electrode. Two mixed conduction phases were studied: Gd0.1Ce0.9O2-δ (GDC) as an infiltrant into Ni-YSZ electrodes, and Ni/transition metal doped-YSZ electrodes infiltrated with Ni. Analysis of impedance data from these cells shows improved electrochemical performance in infiltrated cells with mixed conduction compared with infiltrated cells containing purely ionic and electronic conducting phases. Improved anode performance is attributed to the availability of electronic pathways through predominantly ionic-conducting phases to connect distant Ni nanoparticles and/or Ni grains.

Facet-dependent activity of tailored anatase TiO2 crystals in photoanodes for photocatalytic fuel cells

A key component of the photocatalytic fuel cell (PFC) is a photoanode, typically based on highly stable semiconductor (e.g., TiO2) that is capable of effective photoelectrocatalytic oxidation of fuels. Notably, the photo(electro)catalytic activity of TiO2 materials can depend heavily on the microstructural morphology, so that tailored crystals with different shapes and exposed facets can show remarkably different, shape-dependent photoactivities. Herein, we study the PFC performance of photoanodes based on anatase crystals of various shapes – tetragonal truncated bipyramids, sheets and belts, which are characterized by different predominantly exposed facets: {101}, {001}, and {100}, respectively. We demonstrate that photoanodes based on belt-shaped crystals dominated by {100} facets, not observed in natural anatase crystals, exhibit superior performance. Analysis of open-circuit potential and impedance data suggests that this activity is related to faster transfer of photogenerated holes to methanol oxidation sites, avoiding thus the undesired surface trapping and Fermi level pinning effects that are the most likely reason of a poorer performance of materials dominated by {101} and {001} facets. This study highlights the importance of advanced crystal engineering and control over the surface catalytic properties of TiO2 materials for PFCs and other light-driven devices in which efficient alcohol photooxidation is crucial.

Electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate properties of materials and electrode reactions. This Primer provides a guide to the use of EIS and a comparison with other electrochemical techniques. The analysis of impedance data for reduction of ferricyanide in a KCl supporting electrolyte is used to demonstrate the error structure for impedance measurements, the use of measurement and process models, and the sensitivity of impedance to the evolution of electrode properties. This Primer provides guidelines for experimental design, discusses the relevance of accuracy contour plots to wiring and instrumentation selection, and emphasizes the importance of the Kramers–Kronig relations to data validation and analysis. Applications of EIS to battery performance, metal and alloy corrosion, and electrochemical biosensors are highlighted. Electrochemical impedance measurements depend on both the mechanism under investigation and extrinsic parameters, such as the electrode geometry. Experimental complications are discussed, including the influence of non-stationary behaviour at low frequencies and the need for reference electrodes. Finally, emerging trends in experimental and interpretation approaches are also described. This Primer on electrochemical impedance spectroscopy (EIS) provides an experimental design guide to measure impedance and how these data are analysed. The range of applications that require EIS, from measuring battery performance to electrochemical biosensors, is highlighted. Limitations of the method along with emerging trends in experimental optimizations and data interpretation are also described.

Paradoxical Effect of Chest Wall Compression on Respiratory System Compliance: A Multicenter Case Series of Patients With ARDS, With Multimodal Assessment

Paradoxical Effect of Chest Wall Compression on Respiratory System Compliance: A Multicenter Case Series of Patients With ARDS, With Multimodal Assessment

Tracking the evolution of processes occurring in silicon anodes in lithium ion batteries by 3D visualization of relaxation times

An unconventional electroanalytical method has been used for tracking processes in silicon anodes in lithium ion batteries: a 3D visualization of relaxation times. Impedance data of the electrodes were collected at different potentials and different cycles during cyclic voltammetry, and were treated by means of the Distribution of Relaxation Times (DRT) method. A 3D visualization of the results allowed to identify the formation of a solid electrolyte interphase on the anode, composed of two layers with different relaxation times. Such findings are not possible by conventional analysis of impedance data by modeling with equivalent circuits, nor by simple DRT alone. Additionally, it was possible to observe that the characteristic relaxation time of the lithiation of the Si anode becomes smaller upon cycling, indicating that the material experiences structural transformations that allow it to lithiate faster. This result is relevant to motivate the use of micron-sized particles in the anode.