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Journal Title
Electrochimica Acta
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0013-4686
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Item-typ:Veröffentlichung, Evaluation of kinetic parameters of non-faradic processes in carbon-based electrodes using multisine dynamic electrochemical impedance spectroscopy(Elsevier Science, 2023-01-01); ; ; ; Dynamic Electrochemical Impedance Spectroscopy is a valuable tool to investigate kinetic parameters of non-Faradic processes in symmetric Electrochemical Double Layer Capacitors. Compared to classic Electrochemical Impedance Spectroscopy, the dynamic technique measures the impedance under non-equilibrium condition removing the stationarity requirement and, at the same time, giving the frequency-dependent information of a dynamic process in presence of overpotential. Despite not being a new technique, there is an inherent complexity in the signal sampling and data manipulation to obtain the impedance spectra down to low frequencies (the interesting band for energy storage devices impedance). Few methods to compute the impedance from sampled signals are reported in the literature and under development. For this work the Dynamic Multi-Frequency Analysis algorithm was used to compute the impedance and reconstruct the cyclic voltammetry profile as well. The time-dependency of the kinetic parameters, namely capacitances of double layer and adsorption phenomenon, were extracted from equivalent circuit model regression and the adsorption time constants with a graphical analysis of the impedance spectra dataset during a full charge/discharge cycle. The values of the adsorption capacitance from the model regression are, on average, compatible with the values computed with a common formula showing the reliability of the model regression. The use of a three-electrode compact cell allowed the characterization of both active electrodes independently during operation showing a strong potential dependence on the active material properties. Furthermore, the impedance showed the presence of a side reaction (likely oxygen evolution) connected to the increase of adsorption and double layer capacitances localized on the positive electrode in a clearer way than what was possible to observe from the voltametric profile.Wissenschaftlicher ArtikelBand:43745 71 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Self-discharge in Li-ion aqueous batteries: A case study on LiMn2O4(Elsevier Science, 2021-03-20); ; ; ; Aqueous rechargeable lithium-ion batteries have attracted great attention as an alternative to traditional battery technologies, being able to overcome the issues caused by flammable and expensive organic electrolytes. In particular, LiMn2O4 has reached very fast second-level charge capability by the synthesis of unconventional morphology and particle sizes, allowing charging rates up to 600 C and 93% retention of the capacity after 10,000 cycles. However, the self-discharge process and aging mechanisms for aqueous batteries have been rarely studied, which contrasts with the extensive bibliography of the same phenomena in LMO cells based on organic electrolytes. In this article, the mechanisms involved in the loss of reversible specific charges were studied by diverse techniques like OCV, EIS, and In-situ Raman. The results revealed a more favorable self-discharge process compared with using organic electrolytes owing to the lower stability of water. The self-discharge process can be divided into three different regions with a sequential lower decay rate of voltage and capacity as well as two different evolutions of the electric parameters. This study opens new questions about the nature, composition, and mechanisms of the self-discharge in aqueous media which will play a critical role in the electrochemical performance of novel aqueous Li-ion batteries.Wissenschaftlicher ArtikelBand:373102 46 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Extracting the kinetic parameters of the hydrogen evolution reaction at Pt in acidic media by means of dynamic multi-frequency analysis(2019-06-10); ; ; Herein, we use dynamic multi-frequency analysis (DMFA) to investigate the reaction kinetics of a paradigm electro-catalytic reaction, i.e. the hydrogen evolution reaction (HER) at polycrystalline Pt electrodes in acidic media. DMFA allows measuring dynamic impedance spectra under non-steady state conditions, as it is the case to avoid the formation of hydrogen bubbles. The extracted impedance spectra were fitted using electrical equivalent circuits (EECs) based on an analytical model, which took into account a Volmer-Tafel mechanism for hydrogen evolution. We found that the EECs based on this model can serve as suitable electrical analog in order to describe the physico-electrochemical processes that govern the different stages of the HER.Wissenschaftlicher Artikel225 361 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Modeling of electrochemical oxide film growth – impact of band-to-band tunnelingThe Point Defect Model (PDM) describes the corrosion resistance properties of oxide films based on interfacial reactions and defect transport, which are affected by the electric field inside the oxide film. The PDM assumes a constant electric field strength due to band-to-band tunneling (BTBT) of electrons and the separation of electrons and holes by high electric fields. In this manuscript we present a more complex expansion of the common models to simulate steady state oxide films to test this assumption. The R-PDM was extended by including the transport of electrons and holes and BTBT. It could be shown that BTBT only occurs in very rare cases of narrow band gaps and high electric fields and the impact of electrons and holes does indeed lead to a buffering effect on the electric field, but does not lead to a constant electric field strength. Modeling the transport of electrons and holes on the oxide film allows to specifically estimate their potential impact on the film growth. Especially during modeling of oxide films with narrow band gap and/or electrochemical reactions at the film/solution interface the electrons and holes needs to be included to the model.Wissenschaftlicher Artikel160 112 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Dynamic impedance spectroscopy of LiMn2O4 thin films made by multi-layer pulsed laser deposition(2020-01-20); ; ; ; The kinetics of the reversible insertion of lithium ions assisted by aqueous environment into thin film fabricated by multi-layer pulsed laser deposition is studied using dynamic multi-frequency analysis (DMFA). This method allowed us to acquire time resolved impedance spectra in the range of 210 kHz to 11.5 Hz during cyclic voltammetry. The impedance spectra obtained comprises of two RC time constants (semi-circles) indicating that the reversible insertion process of lithium ions in thin films in aqueous media follows a two-stage intercalation process with the first stage as the (de)solvation step of the lithium ions and the second stage as a (de)insertion process with a concurrent change in the oxidation state of manganese. The temporal development of the kinetic parameters with the state of charge during the voltage sweep was investigated and reported in this work.Wissenschaftlicher ArtikelHeft:331313 454 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Modeling of electrochemical oxide film growth-a PDM refinementThe Point Defect Model (PDM) is known for over 40 years and has brought deeper insight to the understanding of passivity. During the last decades it has seen several changes and refinements, and it has been widely used to analyze growth kinetics of different alloys. Nevertheless, the model has been based on still unconfirmed assumptions, as constant and potential independent electric field strength. To overcome this limitation, we introduce a Refined PDM (R-PDM) in which we replace those assumptions by using additional equations for charge distribution including new physically valid boundary conditions based on considering finite dimensions for the defects by introduction of two defect layer at the film boundaries and by calculating the potential drop at the surface of the film towards the solution over the compact double layer. The calculations by the R-PDM show that the original PDM assumptions are only valid for very specific parameter combinations of oxide film growth and vacancies transport and cannot generally be taken for granted. We believe our findings of electric field and potential drop dependency on the external potential to pave the way for a more realistic description of passive layer formation.Wissenschaftlicher Artikel174 110 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, On the physical definition of dynamic impedance: How to design an optimal strategy for data extraction(2019-05-01); Dynamic electrochemical impedance spectroscopy (DEIS) has attracted the interest of researchers due to its capability of acquiring impedance spectra of non-stationary systems in a broad range of frequencies. Although developed in the 70's, a physical definition of dynamic impedance, and in general of dynamic transfer function, is not present in literature. In this manuscript the general concept of dynamic frequency response is given in correlation to the Volterra series expansion: this can be used to define the ideal dynamic impedance response of an electrochemical system. It is clarified that DEIS is the intermodulation of the ac signal with the dc signal. Starting from this, different strategies for the extraction of the dynamic impedance spectra are compared, which are based on different heuristic definitions of DEIS. There are two main methodologies, one based on the use of window functions and the other on quadrature filters. Limits and merits of the different methodologies are discussed in the frame of the data analysis and data handling and show that window functions suffers at recovering low-frequencies impedances while quadrature filters work best in experiments which have a periodic or quasi-periodic trend.Wissenschaftlicher ArtikelHeft:304305 371