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A systematic analysis of knocking combustion at the knock limit in a single-cylinder research engine is conducted. Both experimental and numerical methods are used to investigate the physical phenomena involved in knocking combustion. While real gasoline fuel can be used directly in experimental studies, this is not feasible in numerical simulations. Here, surrogate fuels with a reduced number of components defined to match the desired properties, such as knock resistance, are employed. In this work, standard gasoline and three surrogate fuels are considered. Differences in composition complexity are covered by selecting isooctane and two toluene reference fuels (TRF) with ethanol addition, all of which exhibit negative temperature coefficient (NTC) behavior in which auto-ignition delay times increase with increasing temperature. Spark timing sweeps at two engine speeds show that the knock resistance of the fuels correlates with the respective research octane number (RON). Isooctane is found to have higher knock resistance and higher sensitivity to engine speed than standard gasoline. One of the two TRFs studied shows good agreement with gasoline in terms of combustion and knock characteristics. The lower knock resistance of the other TRF indicates a non-linear dependence between mixture composition and knock resistance. A strong relative increase in knock resistance at higher engine speeds suggests a possible influence of NTC behavior at lower engine speeds. In the subsequent model-based analysis, the fuel influence on combustion and auto-ignition is investigated, and the laminar burning velocities are found to correlate well with the observed heat durations. While auto-ignition may be triggered by a cool spot at the lower engine speed and at operating conditions within the NTC regime, auto-ignition at the higher engine speed is assumed to be initiated by hot spots. These different mechanisms for initiating auto-ignition were identified as a potential explanation for the different knock resistances observed.

Cryo-focused ion beam milling of frozen-hydrated cells and subsequent cryo-electron tomography (cryo-ET) has enabled the structural elucidation of macromolecular complexes directly inside cells. Application of the technique to multicellular organisms and tissues, however, is still limited by sample preparation. While high-pressure freezing enables the vitrification of thicker samples, it prolongs subsequent preparation due to increased thinning times and the need for extraction procedures. Additionally, thinning removes large portions of the specimen, restricting the imageable volume to the thickness of the final lamella, typically < 300 nm. Here, we introduce Serial Lift-Out, an enhanced lift-out technique that increases throughput and obtainable contextual information by preparing multiple sections from single transfers. We apply Serial Lift-Out toC. elegansL1 larvae yielding a cryo-ET dataset sampling the worm’s anterior-posterior axis and resolve its ribosome structure to 7 Å, illustrating how Serial Lift-Out enables the study of multicellular molecular anatomy.

The present study aimed to examine the relationship between perfectionism, OCD symptom dimensions, harm avoidance, and incompleteness at varying levels (i.e., higher-order/subscale) in college students. College students (n= 548) completed measures of perfectionism, obsessive-compulsive symptoms, harm avoidance and incompleteness. The results revealed that all five higher-order dimensions of perfectionism were related to incompleteness but only three were related to harm avoidance. Parallel mediation revealed an indirect relationship between concern for mistakes and doubts about actions and checking and cleaning behaviors, respectively, through incompleteness. An indirect relationship between concern for mistakes and doubts about actions with ordering, respectively, through both incompleteness and harm avoidance was found. However, incompleteness played a stronger role than harm avoidance in this relationship. These results suggest that incompleteness might be a stronger motivator than harm avoidance for perfectionistic individuals. Therefore, interventions targeting incompleteness should be implemented to potentially circumvent the development or worsening of obsessive-compulsive symptoms.

In most bacteria, division depends on a cytoskeletal structure, the FtsZ ring, that functions as a scaffold to recruit additional proteins, with which it forms the machinery responsible for division, the divisome. The detailed architecture of the ring, in particular the mechanisms of assembly, stabilization, and disassembly, are still largely unknown. Here, we highlight the role of FtsZ-associated proteins (Zaps) that stabilize the FtsZ ring by crosslinking the filaments. Among Zap proteins, ZapD binds the C-terminal domain of FtsZ, which serves as a hub for its regulation. We demonstrate that ZapD crosslinks FtsZ filaments into ring-like structures formed by a discontinuous arrangement of short filaments. Using cryo-electron tomography combined with biochemical analysis, we reveal the three-dimensional organization of the ring-like structures and shed light on the mechanism of FtsZ filament crosslinking by ZapD. Together, our data provide a model of how FtsZ-associated proteins can stabilize FtsZ filaments into discontinuous ring-like structures reminiscent of that existing in the bacterial cell., This project has been supported by the Max Planck-Bristol Centre for Minimal Biology (A.M.-S.) and the Deutsche Forschungsgemeinschaft (P. S.). J.S. and M. Jasnin are supported by the French Agence Nationale de la Recherche (ANR) and the Deutsche Forschungsgemeinschaft (DFG) call ANR-DFG 2020 NLE for the project no. JA-3038/2-1 (to M. Jasnin). J.-H.K. is funded by the Germany’s Excellence Strategy – EXC-2094 – 390783311. This work was also supported by the Spanish Government through Grant PID2019-104544GB-I00/AEI/10.13039/501100011033 (M.Jimenez, C.A. and G.R.). M.S.-S. was supported by European Social Fund through Grant PTA2020-018219-I/AEI/10.13039/501100011033. J.R.L.-O and M S.-S. acknowledge support from the Molecular Interactions Facility at the CIB Margarita Salas-CSIC. A.M.-S and J.-H.K. are part of IMPRS-LS, J.-H.K. is also a CeNS Center for NanoScience associate.

Flow, turbulence and combustion (2022). doi:10.1007/s10494-022-00351-9, Published by Springer Science + Business Media B.V., Dordrecht [u.a.]

CASE A 30-year-old man was in a motorcycle accident resulting in an avulsion fracture of the tibial insertion of the posterior cruciate ligament (PCL). After 19 months of nonoperative treatment, the patient presented with a nonunion and symptoms of pain and instability. He was treated with an open repair with screw fixation through a posterior approach. Six months postoperatively, the patient returned to his work as a heavy laborer with full range of motion and no instability. CONCLUSION PCL avulsion fracture nonunion results in symptoms of swelling, pain, and instability. These symptoms can be treated with screw fixation through a posterior approach.

Highly porous carbon–carbon composite electrodes for the implementation in redox flow battery systems have been synthesized by a novel soft-templating approach. A PAN-based carbon felt was embedded into a solution containing a phenolic resin, a nitrogen source (pyrrole-2-carboxaldehyde) and a sulfur source (2-thiophenecarboxaldehyde), as well as a triblock copolymer (Pluronic® F-127) acting as the structure-directing agent. By this strategy, highly porous carbon phase co-doped with nitrogen and sulfur was obtained inside the macroporous carbon felt. For the investigation of electrode structure and porosity X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and nitrogen sorption (BET) were used. The electrochemical performance of the carbon felts was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The N- and S-doped carbon electrodes show promising activity for the positive side reaction and could be seen as a significant advance in the design of carbon felt electrodes for use in redox flow batteries.

This paper addresses the damaging role of the parasitic hydrogen evolution reaction (HER) in the negative half-cell of a vanadium redox flow battery (VRFB) on state-of-the-art carbon felt electrodes at different temperatures. It was found that increasing the temperature resulted in a better catalytic performance for both the positive and negative half-cell reactions. In addition, increasing the temperature significantly enhanced the undesired HER at the negative side. Operating the VRFB cell at higher temperature led to a decrease in the coulombic efficiency attributed to the higher hydrogen production. More pronounced hydrogen production caused an oxidation on the surface of the carbon fibers and a degradation of the electrode as indicated from scanning electron microscopy and X-ray photoelectron spectroscopy measurements. This observed degradation results in fading of the overall performance of the vanadium redox flow battery over time.

In order to quantitatively investigate the kinetic performance and the pore size distribution of carbon felt electrodes for the application in vanadium redox flow batteries, the theory of cyclic voltammetry (CV) is derived for a random network of cylindrical microelectrodes on the base of convolutive modeling. In this context we present an algorithm based on the use of a modified Talbot contour for inverse Laplace transformation, providing the mass transfer functions required for the calculation of the CV responses in external cylindrical finite diffusion space. First-order homogenous chemical kinetics preceding and/or following the electrochemical reactions are implemented in this algorithm as well. The VO2+ oxidation is investigated as model reaction at pristine and electrochemically aged commercial carbon felt electrodes. A fit of simulated data to experimental data clearly shows that an electrochemical aging predominantly affects the kinetics of the electron transfer reaction and that internal electrode surfaces and pore size distributions remain constant. The estimated pore size distributions are in excellent agreement with porosimetry measurements, validating our theory and providing a new strategy to determine electrode porosities and electrode kinetics simultaneously via CV.

Carbon felts are commonly utilized electrodes in vanadium flow batteries due to their low cost, light weight, good electronic conductivity, and chemical inertness. In contrast, their activity in catalyzing the vanadium redox reactions is less remarkable. In particular at the negative side, where V3+ reduction competes with the parasitic hydrogen evolution reaction (HER) at low potentials. In the literature, the addition of Bi3+ into the electrolyte [1] or its deposition on the felts has been suggested as a remedy. However, it is not clear yet, whether the Bi decoration remains stable with time and cycling and which mechanisms are responsible for the observed performance increase. The aim of this work is therefore to unravel more details about the catalyzing effect of Bi and its stability on the cell level. To this effect, the electrode kinetics with and without Bi decoration were studied comparing results obtained using Friedl’s method [2] with cyclic voltammetry (CV) data analyzed by the Polarographica curve fitting routine [3]. This approach can also be generalized to obtain precise kinetic information with other decorating metals. We furthermore applied negative dynamic hydrogen bubble templating (DHBT) deposition as an interesting way to coat commercially available carbon felts with a structured metallic layer of high surface area. Using this strategy, a significant positive effect was observed. However, the drying parameters and post-processing of the felts are important parameters which severely affect the final performance. In order to study the stability of Bi deposits in realistic battery experiments, in-situ synchrotron radiography has been used to monitor the Bi-decorated felts during charge-discharge cycles [4]. The figure demonstrates the effect of different flow rates on the Bi deposition patterns. Dark spots show metal-decorated areas within the felts at flow rates of 5 mlmin-1 (left), 15 mlmin-1 (middle) and 25 mlmin-1 (right). It can be easily seen that the operation conditions influence the felt decoration significantly, while Bi deposits dissolve and deposit during the charge-discharge routine. Further studies will be necessary to find out a) whether different deposit positions affect the performance enhancement and b) if DHBT-Bi remains more stable under operating conditions. In our presentation, we will not only focus on the materials, but also highlight techniques especially suitable for the stuctural and electrochemical analysis of felt electrodes. [1] B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. Wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, W. Wang, Bismuth Nanoparticle Decorating Graphite Felt as a High-Performance Electrode for an All-Vanadium Redox Flow Battery, Nano Letters 13(3) (2013) 1330-1335. [2] J. Friedl and U. Stimming, Determining Electron Transfer Kinetics at Porous Electrodes, Electrochim. Acta 227 (2017) 235–245. [3] T. Tichter, J. Schneider, D. Andrae, M. Gebhard, and C. Roth, Universal algorithm for simulating and evaluating cyclic voltammetry atmacroporous electrodes by considering random arrays of microelectrodes, ChemPhysChem 21 (2019) 428 –441. [4] M. Gebhard, T. Tichter, J. Schneider, J. Mayer, A. Hilger, M. Osenberg, M. Rahn, I. Manke, C. Roth J. Power Sources 478 (2020) 228695. Figure 1

Many organisms, when alone, behave differently from when they are among a crowd. Drosophila similarly display social behaviour and collective behaviour dynamics within groups not seen in individuals. In flies, these emergent behaviours may be in response to the global size of the group or local nearest-neighbour density. Here we investigate i) which aspect of social life flies respond to: group size, density, or both and ii) whether behavioural changes within the group are dependent on olfactory support cells. Behavioural assays demonstrate that flies adjust their interactive behaviour to group size but otherwise compensate for density by achieving a standard rate of movement, suggesting that individuals are aware of the number of others within their group. We show that olfactory support cells are necessary for flies to behave normally in large groups. These findings shed insight into the subtle and complex life of Drosophila within a social setting., Rooke, Rasool et al. show that Drosophila melanogaster flies can detect the number of individuals around them and modify their behaviour based on group size and density. Furthermore, they show that LUSH-expressing cells are necessary for group size detection, suggesting the importance of olfactory support cells in modulating collective social behaviours.

Animals interact with each other in species-specific reproducible patterns. These patterns of organization are captured by social network analysis, and social interaction networks (SINs) have been described for a wide variety of species including fish, insects, birds, and mammals. The aim of this study is to understand the evolution of social organization in Drosophila. Using a comparative ecological, phylogenetic, and behavioral approach, the different properties of SINs formed by 20 drosophilids were compared. We investigate whether drosophilid network structures arise from common ancestry, a response to the species’ past climate, other social behaviors, or a combination of these factors. This study shows that differences in past climate predicted the species’ current SIN properties. The drosophilid phylogeny offered no value to predicting species’ differences in SINs through phylogenetic signal tests. This suggests that group-level social behaviors in drosophilid species are shaped by divergent climates. However, we find that the social distance at which flies interact correlated with the drosophilid phylogeny, indicating that behavioral elements of SINs have remained largely unchanged in their evolutionary history. We find a significant correlation of leg length to social distance, outlining the interdependence of anatomy and complex social structures. Although SINs display a complex evolutionary relationship across drosophilids, this study suggests that the ecology, and not common ancestry, contributes to diversity in social structure in Drosophila.

An algorithm for the simulation and evaluation of cyclic voltammetry (CV) at macroporous electrodes such as felts, foams, and layered structures is presented. By considering 1D, 2D, and 3D arrays of electrode sheets, cylindrical microelectrodes, hollow‐cylindrical microelectrodes, and hollow‐spherical microelectrodes the internal diffusion domains of the macroporous structures are approximated. A universal algorithm providing the time‐dependent surface concentrations of the electrochemically active species, required for simulating cyclic voltammetry responses of the individual planar, cylindrical, and spherical microelectrodes, is presented as well. An essential ingredient of the algorithm, which is based on Laplace integral transformation techniques, is the use of a modified Talbot contour for the inverse Laplace transformation. It is demonstrated that first‐order homogeneous chemical kinetics preceding and/or following the electrochemical reaction and electrochemically active species with non‐equal diffusion coefficients can be included in all diffusion models as well. The proposed theory is supported by experimental data acquired for a reference reaction, the oxidation of [Fe(CN)6]4− at platinum electrodes as well as for a technically relevant reaction, the oxidation of VO2 + at carbon felt electrodes. Based on our calculation strategy, we provide a powerful open source tool for simulating and evaluating CV data implemented into a Python graphical user interface (GUI)., Simulating CV: The theory of cyclic voltammetry (CV) at macroporous electrodes is developed by considering random 1D, 2D and 3D arrays of microelectrodes. A universal algorithm for simulating the CV responses of the individual planar, cylindrical and spherical microelectrodes, is presented as well. Experimental data support the proposed model. Finally, an innovative strategy for CV data evaluation is provided and implemented into an open source software tool.

INTRODUCTION: Sleep restriction may lead to decreased performance and increased accidents and errors. SPHERES, a small satellite testbed, was used to examine the effects of sleep restriction and situation awareness (SA) aids on a simulation of satellite operations.METHODS: Subjects (N = 8) were trained on SPHERES, then, in a randomized order cross-over design, had 3 d of sufficient sleep (SS) or 3 d of sleep restriction (SR) before a testing session. Subjects controlled two SPHERES satellites in a space debris avoidance scenario. Dependent measures included survival time, area covered by the satellites, and satellite motion perception.RESULTS: There were significant interaction effects of sleep protocol Order (SS or SR first) and sleep Condition (SS or SR) on survival time and area covered. Post hoc tests showed longer survival time for the second testing session if the Order was SS first (Mean = 56.1 s, Median = 44.0 s) as compared to SR first (Mean = 42.7 s, Median = 33.5 s). SS-first subjects received benefit from added SA cues of the augmented display in perceiving the satellite motion.DISCUSSION: These data support that learning in a well-rested state may support development of appropriate strategies for better performance. Subjects that were SS during the first session were better able to use added SA cues provided by the augmentation and may have then developed a better mental model of the task and the system. This pilot study suggests that training guidelines for operating multiple robotic assets should permit appropriate rest before and after training to assist in mental model development and task performance.Schneider J, Saenz-Otero A, Klerman E, Stirling L. Strategy development pilot study of sleep-restricted operators using small satellites with displays. Aerosp Med Hum Perform. 2018; 89(12):1036-1044.

The constant phase element (CPE) is a well-established circuit component for the frequency domain simulation of electrochemical reactions at disperse and heterogeneous electrodes. Computing the time-dependent current response of voltammetric experiments with interfacial CPE behaviour is, however, not a straightforward task, owing to the lack of analytical time domain solutions of the convoluted capacitive current. In this paper, a universal framework for the convolutive treatment of cyclic voltammetry (CV), alternating current cyclic voltammetry (ACCV), (large) sine wave voltammetry (LSWV) and electrochemical impedance spectroscopy (EIS) in presence of interfacial CPEs and uncompensated Ohmic resistances is presented. A combination of numerical and analytical inverse Laplace transformation techniques allows the accurate assessment of the non-ideal capacitive behaviour, which can be used in turn for classical convolution algorithms. The convolutive approach bears the advantage that different electrode geometries with any kind of spatial boundary conditions as well as first order homogeneous chemical reactions, coupled to the charge transfer step, can be implemented readily. This offers an exceptionally large degree of flexibility in the simulations for the electrochemical system at hand.

We report a new limitation on the ability of physical systems to perform computation -- one that is based on generalizing the notion of memory, or storage space, available to the system to perform the computation. Roughly, we define memory as the maximal amount of information that the evolving system can carry from one instant to the next. We show that memory is a limiting factor in computation even in lieu of any time limitations on the evolving system - such as when considering its equilibrium regime. We call this limitation the Space-Bounded Church Turing Thesis (SBCT). The SBCT is supported by a Simulation Assertion (SA), which states that predicting the long-term behavior of bounded-memory systems is computationally tractable. In particular, one corollary of SA is an explicit bound on the computational hardness of the long-term behavior of a discrete-time finite-dimensional dynamical system that is affected by noise. We prove such a bound explicitly., 6 pages

"Este proyecto de investigación se realizó con el fin de desarrollar pensamiento crítico en los estudiantes de décimo grado de la Institución Educativa El Tesoro en el municipio del Líbano al norte del Tolima. Esto, se llevó a cabo a través de la implementación de una estrategia pedagógica de lectura crítica en textos periodísticos basado en el método de desarrollo de pensamiento crítico de Richard y Elder (2003). Así mismo se tomó teorías de Cassany (2006) y otras investigaciones como Lara y Rodríguez (2016), para el diseño de las actividades de la intervención en el ciclo de investigación acción. Para llevar a cabo nuestro objetivo y responder la pregunta de nuestro estudio se realizó un ciclo de investigación acción en un grupo de 12 estudiantes pertenecientes a la zona rural. Además, las actividades se llevaron a cabo en el área de lengua castellana, dirigidas por el docente miembro de nuestro grupo de investigación." -- Tomado del Formato de Documento de Grado. "This research project was carried out in order to develop critical thinking in the tenth grade students of El Tesoro Educational Institution in the municipality of Líbano north of Tolima. This was carried out through the implementation of a pedagogical strategy of critical reading in journalistic texts based on the method of critical thinking development of Richard and Elder (2003). Likewise, the theories of Cassany (2006) and other researches such as Lara and Rodríguez (2016) were taken for the design of the activities of the intervention in the action research cycle. To carry out our objective and answer the question of our study, an action research cycle was carried out in a group of 12 students belonging to the rural area. In addition, the activities were carried out in the Castilian language area, led by the teacher member of our research group." -- Tomado del Formato de Documento de Grado. Magíster en Educación Maestría

The facultative pathogen Staphylococcus aureus colonizes the human anterior nares and causes infections of various organ systems. Which carbon, energy, and phosphate sources can be utilized by S. aureus in nutrient-poor habitats has remained largely unknown. We describe that S. aureus secretes a glycerophosphodiesterase (glycerophosphodiester phosphodiesterase, EC 3.1.4.46), GlpQ, degrading the glycerophosphodiester (GPD) head groups of phospholipids such as human phosphatidylcholine (GroPC). Deletion of glpQ completely abolished the GroPC-degrading activity in S. aureus culture supernatants. GroPC has been detected in human tissues and body fluids probably as a result of phospholipid remodelling and degradation. Notably, GroPC promoted S. aureus growth under carbon- and phosphate-limiting conditions in a GlpQ-dependent manner indicating that GlpQ permits S. aureus to utilize GPD-derived glycerol-3-phosphate as a carbon and phosphate sources. Thus, S. aureus can use a broader spectrum of nutrients than previously thought which underscores its capacity to adapt to the highly variable and nutrient-poor surroundings. This article is protected by copyright. All rights reserved.

The social environment modulates gene expression, physiology, behaviour and patterns of inheritance. For more than 50 years, this concept has been investigated using approaches that include partitioning the social component out of behavioural heritability estimates, studying maternal effects on offspring, and analysing dominance hierarchies. Recent advances have formalized this 'social environment effect' by providing a more nuanced approach to the study of social influences on behaviour while recognizing evolutionary implications. Yet, in most of these formulations, the dynamics of social interactions are not accounted for. Also, the reciprocity between individual behaviour and group-level interactions has been largely ignored. Consistent with evolutionary theory, the principles of social interaction are conserved across a broad range of taxa. While noting parallels in diverse organisms, this review uses Drosophila melanogaster as a case study to revisit what is known about social interaction paradigms. We highlight the benefits of integrating the history and pattern of interactions among individuals for dissecting molecular mechanisms that underlie social modulation of behaviour.

Decorating carbon felt electrodes with bismuth and bismuth oxide nanoparticles is proposed to be a promising strategy for enhancing the sluggish electron transfer kinetics of the negative half-cell reaction in vanadium redox flow batteries. However, regarding the highly corrosive electrolyte solution, major concerns on the stability of the solid bismuth phase and thus on the local catalyst distribution and catalyst functionality emerge. With this study we present a novel in-operando cell design allowing for X-ray imaging during battery tests in laboratory scale dimensions. In this manner, we verify a dissolution of the bismuth/bismuth oxide particles in open circuit potential condition at SOC = 0 (SOC: state of charge) as well as a re-deposition during the charging process of the battery. No dissolution during the discharging process can be detected. With this knowledge, the effect of the bismuth/bismuth oxide distribution on the electrochemical performance of the battery is investigated. By performing the deposition during the charging process at different electrolyte flow rates, different deposition patterns are obtained. However, independent of the deposition pattern, similar cell performances are achieved that put the enhancement effect by bismuth as heterogeneous catalyst into question.

Recent studies[1,2] suggest that ion crossover through the membrane of a vanadium redox-flow battery (VRFB) can not be considered the only source of irreversible capacity loss. Instead, degradation of the macroporous carbon felt electrodes has to be taken into account as well. Especially in the negative half-cell, any degradation-induced alteration of the fibres’ surface composition will significantly impede the kinetics of the V2+/V3+ redox-system. Since the resulting increase in kinetic overvoltage will limit the accessible capacity, a reasonable lifetime prediction of a VRFB is only possible if all aspects of capacity fade mechanisms, including electrode degradation are well understood. This raises the demand for a measurement technique, which allows for in-operando state-of-health-assessment of the electrodes in a non-invasive fashion. Employing electrochemical impedance spectroscopy (EIS), the characteristics of any electrochemical system can be easily probed by applying non-harmful, small-amplitude sinusoidal perturbations. Interpretation of EIS usually relies on fitting suitable equivalent circuit models to experimental data. However, validation of such models can be a cumbersome task due to the inherent ambiguity of EIS, meaning that different circuits may approximate the same data set equally well. Furthermore, a full cell spectrum will always yield a superposition of the respective half-cell impedances. Discriminating the contributions of the individual half-cell electrodes to the impedance of a VRFB has therefore been attempted by implementing reference electrodes. However, these are known to be a source of artefacts and distortion in the high frequency range. In the present study we apply the distribution of relaxation times (DRT) analysis[3] to EIS data of a single cell VRFB. This innovative approach allows us to resolve up to three different time constants per frequency decade. It therefore enables processes that overlap in the classical Bode- and Nyquist representation to be displayed as distinct peaks. Consequently, the individual half-cells can be studied from full cell spectra, circumventing the necessity of finding appropriate equivalent circuit models and rendering the implementation of reference electrodes obsolete. We outline our experimental strategy for unravelling the physical nature of the processes related to the individual signals in the DRT spectrum and finally demonstrate how these findings enable an online monitoring of electrode degradation in VRFB. Keywords: electrochemical impedance spectroscopy, distribution of relaxation times, electrode degradation, vanadium redox-flow battery References: [1] I. Derr et al., Electrochim. Acta 2017, 224, 9-16. [2] O. Nibel et al., J. Electrochem. Soc. 2017, 164, A1608-A1615. [3] E. Ivers-Tiffée, A. Weber, J. Ceram. Soc. Japan 2017, 125, 193-201. Figure 1: DRT analysis of a single cell VRFB: complex-plane plot of measured impedance (top) and DRT representation (bottom). Figure 1

A novel four-step strategy for real-space simulation of cyclic voltammetry (CV) at carbon felt electrodes is presented, circumventing the diffusion domain approximation approach used so far for CV simulation at porous electrodes. At first, the three-dimensional template of the internal electrode structure is constructed from micro X-ray tomography measurements. Subsequently, by exploiting the Douglas–Gunn modification of the three-dimensional Crank–Nicolson algorithm to Cottrellian boundary conditions, the mass transfer controlled current of this ”true” network is obtained. Based on this current, the third step is to compute the mass transfer functions related to the electrode under investigation by an inverse convolution algorithm. In this manner, the spatial dimensionality of the system is reduced from three to one, resulting in significant savings in computation time. The fourth and final step is then to simulate CV experiments via classical convolution methods, featuring the great advantage that any degree of electrochemical reversibility, coupled homogeneous reactions, electrolyte resistances and double layer capacities can be implemented readily. As a proof of concept, the simulations are supported by experimental data acquired for the oxidation of VO2+ in carbon felt electrodes.

Cyclic voltammetry (CV) is the prevalently used technique for investigating the kinetic performance of carbon felt electrodes for application as porous electrocatalysts in vanadium redox-flow batteries. However, the theoretical treatment of internal diffusion-reaction phenomena of such electrodes, allowing for quantitative data evaluation, is still unexplored and mostly relies on diffusion domain approximations assuming the felt as an array of either planar, spherical or cylindrical microelectrodes in a randomly distributed and finite diffusion domain. With this study, we present a novel three-step strategy for real-space CV simulation of felt electrodes. By using micro x-ray tomography (CT) data of the felts, we obtain a locally resolved 3D template of the diffusion space making any diffusion domain approximations obsolete. CV simulation involving this real diffusion domain template is performed by combining the implicit Crank-Nicolson technique in 3D with convolutive modelling. At first, by utilizing the Crank-Nicolson method, we obtain the chronoamperometric current of the 3D porous network for Cottrell-like Dirichlet boundary conditions. Subsequently, the mass transfer functions, usually generated with the aid of Laplace integral transformation techniques, are calculated from these chronoamperometric currents. Then, CV simulation is performed on the basis of these mass transfer functions involving classical convolution integrals. This strategy offers three significant advantages. First, we avoid the difficulty of implementing non-Dirichlet boundaries in the matrices of the Crank-Nicolson scheme. Second, the difficulty of performing an inverse Laplace transformation is avoided since no direct Laplace transformation step is involved. Third, once the mass transfer functions are obtained the simulation can be done with significant savings in time since the 3D network is converted into a one-dimensional problem that can be solved via classical convolution integrals. Our simulation is supported by experimental data acquired for the VO2+-oxidation reaction underlining the validity of our approach. Figure 1

Understanding degradation phenomena occurring during the operation of vanadium redox-flow batteries (VRFB) requires a measurement technique which allows for differentiating the overall performance losses into individual performance losses of the cell components. For this purpose, electrochemical impedance spectroscopy (EIS) is a valuable and well established tool. However, the discrimination of processes taking place at similar time scales is challenging since they overlap in the commonly used Nyquist or Bode representation. Distribution of relaxation times (DRT) analysis tackles this issue by deconvoluting EIS data with respect to the time constants of the individual processes. It hence circumvents the necessity of finding a suitable equivalent circuit model and thus allows for data evaluation without any a-priori knowledge of the system under study. For the first time, we herein present the application of DRT transform to EIS data of a VRFB. By varying experimental conditions and employing full cell as well as double half cell operational modes, we are able to identify the faradaic process of the negative half cell. This enables us to visualize the negative half cell’s contribution to the overall impedance of a VRFB even in a full cell EIS measurement. By an accelerated degradation experiment we finally demonstrate the great potential of DRT analysis for future application in the monitoring of electrode degradation in VRFB.

Thin film rotating-ring disc electrode (RRDE) technique is exploited to quantify the parasitic hydrogen evolution reaction (HER) competing with the desired V3+-reduction at surface modified carbon nanoparticles for application as electrocatalysts in the negative half-cell of vanadium redox-flow batteries (VRFB). Carbon based electrode materials are derived from standard Vulcan XC-72 carbon, treated by chemical surface etching techniques proposed for carbon felt-electrodes in the literature. Additional electrochemical characterization is performed using stationary cyclic voltammetry (CV) followed by fitting of CV data, Fourier-transform alternating-current cyclic voltammetry (FT-ACCV) and electrochemical impedance spectroscopy (EIS) followed by distribution of relaxation times (DRT) analysis. To our knowledge the present paper is the first study using the RRDE technique for separating HER and V3+-reduction reactions. It is demonstrated that the ratio of HER to V3+-reduction significantly depends on the chemical pretreatment of the carbon electrodes and that the V3+-reduction proceeds at an optimum rate at E − ERHE = −0.45 V. Separating the HER from the V3+-reduction also allows us to provide highly accurate values for the diffusion coefficient of the V3+-ion in sulfuric acid solutions.