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Designing compatible electrode–electrolyte interfaces is critical to achieve high and consistent performance and life span in next-generation rechargeable lithium batteries. In the study of nanoscopic interfaces, ab initio molecular dynamics (AIMD) simulations allow for a highly accurate description of interface dynamics and reactions. However, due to the high computational cost, simulations are limited in the size and time domains and therefore merit the need for a new interpretational approach that can deduce the long-term reactivity from such short yet highly accurate simulations. In this study, this is established by means of bond length distribution analysis through which the reactivity of key solid polymer electrolyte (SPE) polymer functional groups in contact with key electrode materials (graphite, silicon, lithium) and the influence of the electric field and temperature was successfully determined. Bond length distributions were found to respond to environmental changes and relate to the long-term reactivity in which the strength of electrode surface interactions and the accessibility of functional groups were found to be critical factors. Furthermore, the balancing of the SPE polymer mobility and functional group–electrode surface attraction, respectively, kinetic and thermodynamic properties, further suggests a selective spatial orientation of functional groups when exposed to an electric field, which could have great implications for low-temperature and high-current-density environments. The obtained knowledge on how reactive key SPE polymer functional groups are and also how their reactivity changes in terms of the electric field orientation effect could provide new insights for designing new stable SPE polymers.

Electrorefining is the process of choice to purify several metals, among which is copper. A crucial process parameter in electrorefining, and electroplating in general, is the additive activity. Several additives are introduced to the electrolyte to ensure a morphological smooth copper deposit. Thiourea is a crucial but complex additive used in copper electrorefining, it is known to degenerate and both the reaction product as thiourea itself can complex with the copper ions. Unfortunately, time dependent additive studies and mechanistic knowledge of the effect of aged electrolyte on the cathodic part of the electrorefining process are scarce. In this work, operando Odd Random Phase Electrochemical Impedance Spectroscopy (ORP-EIS) is used to study the electrochemistry of a copper plating system containing industrial copper concentrations. The approach applied enables the investigation of the time-varying effect of additives, in this case thiourea and chlorides, assisting the electroplating of copper.

Accurate surface temperature and recession measurements are crucial experimental data for plasma wind tunnel testing of ablative thermal protection materials. In this work we propose a novel methodology to reconstruct infrared temperature maps on 3D geometries undergoing surface recession. An optical calibration technique is used to extract 3D metric information from the 2D thermal images, thanks to a specific calibration target with control points. The evolution of the sample shape during the experiment is tracked from a side view, using a visual-range camera with dedicated image processing, and reconstructed in 3D under the assumption of axisymmetry. The surface temperature is projected on the time-varying 3D geometry from the calibrated thermograms. The technique is demonstrated on a graphite ablation experiment in air plasma. The reconstructed maps provide detailed multidimensional information about the transient temperature evolution, overcoming traditional approaches that are limited around the stagnation point. The technique allows to study ablation mechanisms with further detail, improving experimental data for material qualification and validation of simulation codes.

In this work, the separate diffusion of water and ions through a polyethylene glycol diacrylate (PEGDA) coating was characterized using an integrated spectro-electrochemical technique. The ions ingress front position profile along the thickness of the coating was derived from fitting odd random phase electrochemical impedance spectroscopy (ORP-EIS) data using a physically relevant electrochemical equivalent circuit (EEC). The arrival time of the ions at the coating/metal oxide buried interface obtained from EEC and rapid uptake of water was verified using in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) measurements in Kretschmann geometry integrated in the ORP-EIS set-up.

Electrochemical machining (ECM) and electropolishing are examples of anodic dissolution used in a wide variety of applications. Proper simulations of ECM require the establishment of a so‐called gel layer of liquid metal salt, responsible for the depletion of water close to the surface such that the oxygen evolution is reduced. However, this effect is neglected in many simulation efforts, although it is significant to improve the accuracy of the machining process. Some authors consider this effect by an engineered “water‐repelling” function that depends on the local metal ion concentration. As an alternative, we discuss the theoretical description and the implementation of modified Poisson–Nernst–Planck equations taking into account expressions in which each ion has its own maximum concentration and corresponding steric limit. We investigate a basic system of water, sodium chloride, and iron ions. Simulations pending on the local metal ion concentration for current densities show that the modified model works; steric effects become important for large current densities and the formation of a resistive gel layer is responsible for the reduction of water at the electrode. We observe that the electrostatic potential resulting from space charge effects is not affected by implementing the different species sizes. Further research is needed to explore the applicability of industrial simulation tools.

High voltage cathodes suffer from degradation phenomena that are challenging to be observed and identified during cell operation. Dense and smooth sputtered thin films electrodes with absence of binders and conductive additives allow a direct study of the active material upon Li insertion and extraction at surface and bulk. Using an operando spectroscopic ellipsometry set-up combined with a customized electrochemical-optical cell (EC-SE), the evolution of the optical absorption and thickness of LiMn2O4 and LiNi0.5Mn1.5O4 thin-film electrodes was monitored upon cycling. Mixed Mn3+/4+ valence in the electrodes and evident layer dissolution associated to Transition Metal (TM) dissolution in the non-aqueous electrolyte at the applied polarization potentials was observed. Our results reaffirm EC-SE as a convenient method to study degradation phenomena in cobalt-free transition metal oxide electrodes.

Equilibria evolving over time, also called trends, are often present in ongoing measurements of real-life systems. These trends are considered as disturbances when computing the Best Linear Time-varying Approximation (BLTVA) of the system. Current techniques for dealing with trends in BLTVA measurements consist of modelling the trend with a finite number of basis functions. However, in measurements with dominant trends, the trend cannot always be captured well enough by this set of basis functions, and, hence, the uncertainty on the BLTVA increases. As a consequence, one looses low frequency information. In this paper, the state-of-the-art method for estimating the BLTVA is extended by removing the trend with a differencing operator. It is shown that with this novel technique, low frequency information becomes more visible. Moreover, the novel method decreases the variance on the BLTVA, and allows to measure fewer periods. Hence, the novel technique improves the route for treating arbitrary out-of-equilibrium, or also called operando, measurements. As an illustration, it is applied to operando time-varying impedance measurements of three electrochemical processes: the charging of a Li-ion battery cell, the electrorefining of copper and the anodising of aluminium.

Electron paramagnetic resonance (EPR) spectroscopy is not considered a standard technique within the electrochemist's toolkit. It was used more frequently in electrocatalysis research from the 1960′s until the 1990′s to identify paramagnetic reaction intermediates and elucidate reaction mechanisms, but is less used nowadays. Since the 1990′s however, technological progress has made advanced EPR methods more readily available, which has allowed for more sensitive measurements and better identification of intermediate species. Furthermore, developments in additive manufacturing have made it easier and cheaper to construct specialized electrochemical cells for EPR research. This review aims to provide a critical overview of contemporary research combining electrocatalysis and EPR, and at the same time spark renewed interest in the combination of these two techniques. It is divided into three sections. Firstly, it covers the challenges involved with in situ cell design and gives an overview of recent cell designs. Next, a number of contemporary mechanistic and quantitative studies are reviewed to explore the possibilities of EPR spectroscopy. Finally, it covers advanced pulse EPR techniques and their (so far) limited use in electrocatalytic research.

Point defects play important and crucial roles in the design of high performance photocatalysts. We report on the electrochemical fabrication of black Ti−Mo-Ni−O nanotubes as a promising electrode material for solar-assisted water splitting. The ternary Ti−Mo-Ni−O catalyst was annealed in hydrogen atmosphere to induce point defects in the material to enhance its conductivity, charge carriers density, and performance. The effect of annealing duration on the performance of ternary Ti−Mo-Ni−O nanotube films was investigated. The hydrogen-annealed nanotubes showed enhanced optical characteristics in the visible spectrum, which can be related to the formation of defect states upon hydrogen annealing. The 10 h-annealed sample showed an exceptionally enhanced photocurrent density of ∼10 mA/cm2 with a remarkable open-circuit voltage of ∼−1.0 VAg/AgCl under AM 1.5G illumination. This improved photocurrent is in agreement with the obtained 75 % incident-photon-to-current-conversion-efficiency (IPCE), confirming the improved photoactivity of the hydrogen-treated mixed oxide nanotubes.

Empirical electrocatalyst research generally consists of the synthesis and experimental characterization of catalysts and the analysis of electrolysis products by conventional analytical techniques.In-situelectron paramagnetic resonance spectro-electrochemistry provides an evidence-based in-depth understanding of the formed intermediates and the reaction mechanism enabling the desired tuning of electrocatalysts. The use of this technique has been underexploited because of the opposite requirements they impose on the conventional setup. In this work, a versatile electrode with commercially available indium tin oxide on polyethylene terephthalate (PET) was constructed for the first time which can fit inside commonly used flat cells. It allows reproducible electrodeposition of catalytic material combined with sensitive radical detection, owing to its large surface area and minimal disruption to the resonator's Q-factor. Moreover, with a resistivity of 8-10 omega sq(-1), the surface potential of the thin semiconductor electrode within the resonator was well-controlled, allowing targeted radical production.

The ionic conductivity of acceptor doped ceria is strongly influenced by grain boundaries and interfaces, with most experiments showing a conductivity decrease in these regions. Classical models explain this observation by the formation of space charge layers, that are depleted of mobile ionic charge carriers. However, some experiments demonstrate an increase in ionic conductivity and recent models show that the space charge layers can also be enriched in mobile ionic species. Because of these discrepancies, it is still not certain whether nanocrystalline or thin film ceria can offer superior ionic conductivity or not. Recently, we have demonstrated by means of Monte Carlo simulations that the ionic conductivity in space charge layers can indeed exceed the bulk value. In this work, we combine these Monte Carlo simulations with a continuum model to predict charge carrier concentration profiles. This multiscale approach allows for a realistic prediction of the grain boundary ionic conductivity.

In this work, hot-dip galvanised steel wires were exposed in Belgium and Indonesia for 4.5 years and correlation of corrosion products formed on the exposed wires with their corrosion properties was studied. Corrosion products were identified with local Raman analysis and correlated with corrosion activity based on odd random phase electrochemical impedance spectroscopy and Tafel behaviour. Raman spectroscopy results confirmed that corrosion products formed in both atmospheric conditions differed either in quantity and/or in chemical nature, which indicated that ‘aged in Belgium’ and ‘aged in Indonesia’ wires did not have similar surface compositions. The comparison of the instantaneous corrosion behaviour of pristine and aged wires based on corrosion currents (polarisation curve) and impedance values in 0.1 M NaCl and 0.1 M Na2SO4 declared that aged in Belgium (AIB) and aged in Indonesia (AII) wires exhibited different corrosion behaviour, which confirmed that corrosion products formed in the environments of the exposed wires were dominating their corrosion behaviour.

Electrochemical impedance spectroscopy (EIS) is a powerful technique for characterization of lithium-ion batteries (LIBs). It has extensively been used in laboratory research, but seldom in industrial applications, e.g., electrical vehicles (EVs). This is because the latter needs EIS measurements during operation, but achieving valid EIS measurements in dynamic conditions has been a long-lasting challenge. In this work, LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite batteries are characterized by operando odd random phase EIS (ORP-EIS) under practical usage conditions. The validity of the EIS data is quantitatively assessed based on the robust theoretical framework of ORP-EIS. The measured impedance data reveals a continuous evolution of charge-transfer phenomena along changes of state-of-charge (SoC). The results are consistent with conventional stationary EIS data. Moreover, charge-transfer related parameters can be extracted through equivalent electric circuit models or graphical analysis methods from operando ORP-EIS. The parameters exhibit consistent behavior under various charging conditions including different temperatures, C-rates, and state-of-health (SoH). As a proof of concept, operando ORP-EIS provides unique physical insights on top of conventional current/voltage-based monitoring methods, and could be powerful technique to monitor the SoC of the batteries during fast charging.

Lithium–ion solvation governs the performance of lithium metal anode (LMA) by tuning its interfacial stability. Solvation degree is modulated by adopting fluorinated non-solvating cosolvents (FNSC) to induce anion-rich solvation structure which is beneficial in constructing mechanically stable interface to suppress lithium dendrite. However, FNSC exhibits low cathodic stability owing to their low lowest unoccupied molecular orbital (LUMO) level, aggravating long-term cycling of LMA. We establish that spectroscopically measured Lewis basicity and polarity are critical parameters for designing optimal non-solvating cosolvents. Non-fluorinated non-solvating cosolvents (NFNSC) proposed by our design rule (i.e. anisole, ethoxybenzene and furan) delivered 99.0 % coulombic efficiency over 1400 cycles. In these molecules, the aromatic ring delocalizes oxygen electron pairs and lowers solvation capability, confirmed by electrochemical cycling, Raman spectroscopy, and DFT binding energy calculation. Finally, the quantification of remaining NFNSC in the electrolytes using nuclear magnetic resonance spectroscopy proves their reductive stability for extended cycles.

The solid–electrolyte interphase (SEI), the passivation layer formed on anode particles during the initial cycles, affects the performance of lithium-ion batteries (LIBs) in terms of capacity, power output, and cycle life. SEI features are dependent on the electrolyte content, as this complex layer originates from electrolyte decomposition products. Despite a variety of studies devoted to understanding SEI formation, the complexity of this process has caused uncertainty in its chemistry. In order to clarify the role of the substituted functional groups of the SEI-forming compounds in their efficiency and the features of the resulting interphase, the performance of six different carbonyl-based molecules has been investigated by computational modeling and electrochemical experiments with a comparative approach. The performance of the electrolytes and stability of the generated SEI are evaluated in both half-cell and full-cell configurations. Added to the room-temperature studies, the cyclability of the NMC/graphite cells is assessed at elevated temperatures as an intensified aging condition. The results show that structural adjustments within the SEI-forming molecule can ameliorate the cyclability of the electrolyte, leading to a higher capacity retention of the LIB cell, where cinnamoyl chloride is introduced as a novel and more sustainable SEI forming agent with the potential of improving the LIB capacity retention.

Coating conducting polymers onto active cathode materials has been proven to mitigate issues at high current densities stemming from the limited conducting abilities of the metal-oxides. In the present study, a carbon coating was applied onto nickel-rich NMC622 via polymerisation of furfuryl alcohol, followed by calcination, for the first time. The formation of a uniform amorphous carbon layer was observed with scanning- and transmission-electron microscopy (SEM and TEM) and X-ray photoelectron spectroscopy (XPS). The stability of the coated active material was confirmed and the electrochemical behaviour as well as the cycling stability was evaluated. The impact of the heat treatment on the electrochemical performance was studied systematically and was shown to improve cycling and high current performance alike. In-depth investigations of polymer coated samples show that the improved performance can be correlated with the calcination temperatures. In particular, a heat treatment at 400 °C leads to enhanced reversibility and capacity retention even after 400 cycles. At 10C, the discharge capacity for carbon coated NMC increases by nearly 50% compared to uncoated samples. This study clearly shows for the first time the synergetic effects of a furfuryl polymer coating and subsequent calcination leading to improved electrochemical performance of nickel-rich NMC622.

In this work, a new methodology is developed to study the initial behaviour of model organic coatings shortly after coming into contact with an aqueous solution, using odd random phase electrochemical impedance spectroscopy (ORP-EIS). The impedance results are resolved over time via the calculation of the instantaneous impedance and fitted with a physically meaningful equivalent circuit. Many physical parameters could be obtained, such as the rapid water uptake, the resistivity of the coatings and the penetration depth of ions in the coatings. The fitting results were verified using differential scanning calorimetry (DSC) and gravimetry.

This article presents a method for estimating a linear time-varying approximation of a general class of nonlinear time-varying (NLTV) systems. It starts from noisy measurements of the response of the NLTV system to a special class of periodic excitation signals. These measurements are subject to measurement noise, process noise, and a trend. The proposed method is a two-step procedure. First, the disturbing noise variance is quantified. Next, using this knowledge, the linear time-varying dynamics are estimated together with the NLTV distortions. The latter are split into even and odd contributions. As a result, the signal-to-nonlinear-distortion ratio is quantified. It allows one to decide whether or not a linear approximation is justifiable for the application at hand. The two-step algorithm is fully automatic in the sense that the user only has to choose upper bounds on the number of basis functions used for modeling the response signal. The obtained linear time-varying approximation is the best in the sense that the difference between the actual nonlinear response and the response predicted by the linear approximation is uncorrelated with the input. Therefore, it is called the best linear time-varying approximation (BLTVA). Finally, the theory is validated on a simulation example and illustrated on two measurement examples: the crystallographic pitting corrosion of aluminum and copper electrorefining.

Aluminum is an appropriate candidate for bipolar plates in proton exchange membrane (PEM) fuel cells because it reduces the final cost and weight of the fuel cell stack in comparison to stainless steel, titanium and graphite. However, a conductive coating layer is essential to protect it against corrosion. In this study, the electrochemical behavior of aluminum coated with titanium and amorphous carbon layers by physical vapor deposition is evaluated. The main goal is to investigate the corrosion protection performance and the possible failure reasons of the coating in sulfuric acid solutions (with different pH values) in the presence of 3 ppm sodium fluoride and elevated temperature (80 C) to mimic the working conditions of PEM fuel cells. To reach our aim, electrochemical tests are combined with surface analysis techniques. It is revealed that at low pH values (pH = 2 and 3), the coating fails due to the acidity of the electrolyte solutions. However, in the electrolyte with pH = 4, present fluoride ions interfere and consequently lead to localized failures. It is noticed that the presence of defects in the coating is a key parameter in the application of coated aluminum as bipolar plates in PEM fuel cells.

The reliability of printed circuit boards (PCB) is at risk due to continuous miniaturization. As a result, PCBs are more susceptible to external factors such as humidity, temperature, contamination, etc., which affect their general performance, leading to failure of electronic devices. Therefore, protection of the devices against these factors is gaining greatly in importance. Plasma polymerization is used as a method to form a protective barrier by applying plasma polymer films on PCBs. However, the humidity robustness of such plasma coatings on the PCB surface is unknown. In this work, several methods were used to characterize two types of plasma-coated PCBs based on 1H,1H,2H-perfluorodecyl acrylate precursor (single-layer and stacked coatings) upon exposure to humidity, temperature, and bias voltage. Modulated-temperature differential scanning calorimetry enabled thermal analysis of the plasma coatings. Electrochemical impedance spectroscopy in combination with the gravimetric moisture vapor sorption technique were used to study the interaction of these coatings with moisture and quantify the water uptake. The results revealed an only 2% increase of the capacitance of the coatings due to water uptake. Direct-current (DC) leakage current measurements were used to study the influence of a bias voltage applied between the electrodes on the coated PCBs upon exposure to cyclic climatic conditions. Electrical DC testing revealed the protective character of the stacked coating, which did not fail under the given stress conditions, in contrast to the single-layer plasma coatings.

Although deep eutectic solvents (DES) and ethylene glycol (EG) electrolytes are gaining ground as media for the electrodeposition of metals, the influence of these electrolytes on the electrode and electrodeposits has not been elaborated before. In this work, we investigate how choline chloride: ethylene glycol based (ChCl:EG) electrolytes interact with the glassy carbon (GC) working surface at different potentials and, how these interactions change during the electrodeposition of iron from 1:2 and 1:4 ChCl:EG electrolytes. GC substrates are exposed to both electrolytes in absence of iron in order to study the pure electrolyte-substrate interactions. Linear sweep voltammetry was used to determine the potential range in which the different reactions occur, while time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to detect and identify the molecules adsorbed on the surface. In all systems, there is an accumulation of either choline or its derivatives on the electrode surface, with 1:4 ChCl:EG electrolytes showing different decomposition products from 1:2 ChCl:EG electrolytes. Choline accumulation and decomposition was also found on iron electrodeposits. The electrolyte composition has a major impact on the chemical speciation of iron, and on the deposit's adherence to the substrate. These are two crucial characteristics that define the efficiency of iron deposition from DES.

Localized high-concentration electrolyte (LHCE) has been adopted to derive resilient inorganic-rich solid-electrolyte interphase (SEI) layer for lithium-metal anodes (LMA) and increase the ionic conductivity of high-concentration electrolyte (HCE). While the ideal diluent molecules used in LHCE should be miscible in electrolyte system, it should not solvate lithium-ion effectively. To date, systematic investigation to reveal the design rule of diluent molecules remain poorly investigated. In addition, the choice of diluents is largely limited to fluorinated organic molecules which are expensive and environmentally hazardous and unstable at the reductive potential. Because of poor cathodic stability, fluorinated diluents (FDs) have failed to achieve cycle lives longer than 500 cycles in lithium metal half-cell. Herein, we establish the design rule of diluents for the ideal LHCE, which allows to derive three non-fluorinated diluents (NFDs) systematically. We present that two solvatochromic parameters, HBA basicity (β) and normalized electronic transition energy (ET N), unravel the generalization rule for the lithium-ion solvation capability and miscibility of diluents. Our design rule discovers three NFDs: anisole, ethoxybenzene, and furan. These NFDs have the unique resonance structures which effectively delocalize the oxygen lone pair electrons and thus enhance non-solvating characteristics, confirmed by the β value and the density functional theory (DFT) calculation. In addition, nuclear magnetic resonance (NMR) spectroscopy studies confirm that our NFDs remains stable and unreacted after long-term cycling. Finally, NFD-containing electrolytes achieve superior cyclability up to 1400 cycles, the record for LHCE to date. The results obtained in this study may pave the way for designing advanced electrolyte for next generation LMA.

Kelvin probe force microscope (KPFM) is an AFM-based technique, which can be used for studying lithium ion batteries (LIBs). The capabilities of this technique for practical applications have been explored further in this work. A direct correlation between the local surface potential measured by KPFM and the electrochemical potential of LiNi 0.80Co 0.15Al 0.05O 2 cathode material is revealed. On the basis of this correlation, a quantitative approach to investigate the local behavior of the cathode material has been developed. We then demonstrate the potentials of this correlation by applying this methodology in three different situations. The surface inhomogeneity of the electrode is visualized and estimated from the microscale down to the nanoscale. In addition, the surface overdelithiation state induced by insufficient Li + solid-state diffusivity is also observed on the electrodes charged at elevated C-rates. Accordingly, it indicates the presence of an uneven delithiation from the surface toward the bulk of the active particle. This work demonstrates that KPFM is a robust technique to investigate LIB systems due to its prominent experimental compatibility, surface sensitivity, and high spatial resolution (

In this work, an improved in-situ EPR hydrodynamic electrochemical cell design is constructed and validated. The created platform enables the fast and accurate screening of new electrocatalytic materials, providing insights into their effects on radical products of a reaction. Furthermore, it is essential that the reaction kinetics are not influenced by the set-up and that mass transfer can be controlled. Our modular design allows for fast and easy replacement of parts and adjustments to electrodes in order to unravel the catalysts' influence on radical formation. The proximity of the pseudo-reference electrode to the working electrode in combination with the flow and electrode positioning allows for good potential control. The POM housing allows easy manipulation of the channel and excludes the use of sealing agents. Keywords: In-situ EPR spectroscopy, Electrochemical flow cell design, Channel electrode, Electrochemical reduction, Radical detection

SCOPUS: ed.j, info:eu-repo/semantics/published

Nickel-containing N-doped carbons were synthesized for the electrochemical reduction of CO2 to CO, which is a promising approach to reduce the atmospheric CO2 levels and its negative impact on the environment. Unfortunately, poor performance (activity, selectivity and/or stability) is still a major hurdle for the economical implementation of this type of materials. The electrocatalysts were prepared through an easily up-scalable and easily tunable method based on the pyrolysis of Ni-containing N-doped carbons. Ni–N–AC–B1 synthesized with a high relative amount of nitrogen and nickel with respect to carbon, was identified as the most promising candidate for this reaction based on its partial CO current density (4.2 mA cm−2), its overpotential (0.57 V) and its faradaic efficiency to CO (>99%). This results in unprecedented values for the current density per g active sites (690 A g−1 active sites). Combined with its decent stability and its high performance in an actual electrolyzer setup, this makes it a promising candidate for the electrochemical reduction of CO2 to CO on a larger scale. Finally, the evaluation of this kind of material in a flow-cell setup has been limited and to the best of our knowledge never included an evaluation of several crucial parameters (e.g. electrolyte type, anode composition and membrane type) and is an essential investigation in the move towards up-scaling and ultimately industrial application of this technique. This study resulted in an optimal cell configuration, consisting of Pt as an anode, Fumatech® as the membrane and 1 M KHCO3 and 2 M KOH as catholyte and anolyte, respectively. In conclusion, this research offers a unique combination of electrocatalyst development and reactor optimization.

The VKI Plasmatron is the world’s largest inductively coupled plasma facility, which allows to reproduce on ground the high-enthalpy, chemically reacting boundary layer over a re-entry body. Test conditions are suitable for qualification of thermal protection systems and for material response studies. This paper presents the experimental investigation of the free-stream air plasma flow under relevant test conditions and the comparison to numerical simulations of the plasma discharge in the test chamber. Previous works have already focused on a similar subject; however, high-resolution spectra over a broad wavelength range, spectral fitting to absolute emission intensities and comparison of experimental temperatures with CFD simulations of the plasma jet were never performed on this facility. Here, the gas-phase radiative signature of dominant atomic and molecular species is observed using a high-resolution spectrograph, combined with a two-dimensional ICCD array. From the rebuilding of local emission intensities, obtained through Abel inversion, radial temperature profiles are determined under the assumption of Local Thermodynamic Equilibrium (LTE). The procedure is based either on fitting the experimental spectra with a line-by-line code (Specair) or by analytical results assuming a Boltzmann’s distribution. The simulated spectra, computed with equilibrium chemical composition and a one-temperature model, agree very well with the experimental data. Magnetohydrodynamics simulations of the plasma jet are then performed using an in-house code and temperature profiles are compared with the experimental gas temperatures at the corresponding locations. Once the power efficiency parameter of the simulation is adequately adjusted, a noticeable agreement is found in the radial distributions at each axial position.

Due to their small size and tremendous speeds, meteoroids often burn up at high altitudes above 80 km, where the atmosphere is rarefied. Ground radio stations allow us to detect the concentration of electrons in the meteoroid trail, which are produced by hyperthermal collisions of ablated species with the freestream. The interpretation of these data currently relies on phenomenological methods, derived under the assumption of free molecular flow, that poorly accounts for the detailed chemistry, diffusion in the vapour phase, and rarefied gas effects. In this work, we employ the direct simulation Monte Carlo (DSMC) method to analyse the detailed flowfield structure in the surroundings of a 1 mm meteoroid at different conditions, spanning a broad spectrum of Knudsen and Mach numbers, and we extract resulting ionization efficiencies. For this purpose, we couple the DSMC method with a kinetic boundary condition which models evaporation and condensation processes in a silicate material. Transport properties of the ablated vapour are computed following the Chapman–Enskog theory starting from Lennard–Jones potentials. Semi-empirical inelastic cross-sections for heavy- and electron-impact ionization of metals are computed analytically to obtain steric factors. The ionization of sodium is dominant in the production of free electrons, and hyperthermal air–vapour collisions play the most important role in this process. The ionization of air, classically disregarded, contributes to the electron production as significantly as ionization of magnesium and iron. Finally, we propose that DSMC could be employed as a numerical experiment providing ionization coefficients to be used in synthetic models.

A comprehensive electrochemical impedance study is conducted on LiNi0.80Co0.15Al0.05O2 electrode material as a function of state-of-charge and aging. Electrodes are harvested from four commercial batteries with different state-of-health conditions. Odd random phase electrochemical impedance spectroscopy and the symmetric cell approach are applied in this work in order to obtain reliable impedance results. An equivalent electrical circuit model is constructed. The parameters related to the generalized finite-space Warburg element, the CPE element and the charge transfer resistance are further interpreted. Valuable information is obtained and closely linked to the physical phenomena. The charge transfer resistance has been proved to be the most reliable parameter for the estimation of state-of-health.

A comprehensive post-mortem study is conducted on the power-optimized LiNi 0.80Co 0.15Al 0.05O 2 (NCA) cathode material harvested from large-format commercial pouch cells with different aging conditions. Uneven degradation phenomena are observed in the harvested NCA electrode during the post-mortem analysis. A schematic model, which is associated with the surface inhomogeneity, is proposed to interpret the formation of uneven degradation phenomena. On the basis of the model, the detrimental impact caused by an elevated cycling temperature is related to the fact that the high cycling temperature facilitates the local overcharge reaction and further accelerates the uneven degradation of the NCA electrodes. This work provides experimental evidence and an in-depth discussion concerning the cycling aging induced from the surface heterogeneity of the electrode material. Additionally, we emphasize the necessity of carrying out a reliable aging study on thin-coated battery electrodes.

For many electrochemical treatments, surface modifications and processes occurring during the relatively short post-treatment time are difficult to monitor using traditional surface analysis techniques. Instantaneous impedance, i.e. time-resolved impedance calculated from an in situ odd random phase multisine electrochemical impedance spectroscopy measurement, may allow for monitoring of these surface modifications. In this work, the AC electrograining process is used as a case study to investigate the possibility of post-electrochemical treatment analysis. It is found that the expected surface changes are indeed found in the instantaneous impedance data. The technique described in this paper can be used to monitor a variety of post-electrochemical treatment surface modifications in situ. Keywords: ORP-EIS, Instantaneous impedance, AC electrograining, Aluminium, Smut layer

Carbon-supported iron complexes were investigated as electrocatalysts for the reduction of nitric oxide (NO) in a H-2-NO fuel cell conceived for the production of hydroxylamine (NH2OH) with concomitant generation of electricity. Two types of iron complexes with tetradentate ligands, namely bis(salicylidene)ethylenediimine (Salen) and phthalocyanine (Pc), supported on activated carbon or graphite were prepared and evaluated as electrocatalysts, either without further treatment or after pyrolysis at 700 degrees C. The performance in the reduction of NO of gas diffusion cathodes based on these electrocatalysts was investigated in an electrochemical half cell (3-electrode configuration) using linear sweep voltammetry (LSV). The most promising electrocatalysts were studied further by chronoamperometric experiments in a H-2-NO fuel cell, which allowed comparison in terms of power output and hydroxylamine production. Depending on the concentration of the NO feed (6 or 18%), the best electrocatalytic performance was delivered either by FePc or FeSalen. The gas diffusion electrode based on FeSalen supported on activated carbon with 0.3 wt% Fe-loading provided the highest current density (86 A/m(2)) and the best current efficiency (43%) towards the desired NH2OH when operating at the higher NO concentration (18%). Moreover, FeSalen offers the advantage of being cheaper than FePc. The experimental work was complemented by density functional theory (DFT) calculations, which allowed to shed more light on the reaction mechanism for the reduction of nitric oxide at the atomistic level.