Koster, Dominique
Lade...
3 Ergebnisse
Gerade angezeigt 1 - 3 von 3
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Dynamic Impedance Spectroscopy of Nickel Hexacyanoferrate Thin Films(2019-10-31); ; ; Dynamic multi-frequency analysis (DMFA) is capable of acquiring high-quality frequency response of electrochemical systems under non-stationary conditions in a broad range of frequencies. In this work, we used DMFA to study the kinetics of (de-)intercalation of univalent cations (Na+ and K+) in thin films of nickel hexacyanoferrate (NiHCF) during cyclic voltammetry. For this system, the classic stationary electrochemical impedance spectroscopy fails due to the instability of the oxidized form of NiHCF. We are showing that such spectra can be fitted with a physical model described by a simple two-step intercalation mechanism: an adsorption step followed by an insertion step. The extracted kinetic parameters are depending on the state of charge as well on the nature of the inserted cation.Wissenschaftlicher ArtikelBand:6Heft:21268 325 - 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, Nonstationary Impedance Measurements in Forced and Natural Dynamic Conditions using Dynamic Multi-Frequency Analysis(2019-10-22); ; ; This thesis is concerned with the characterization of electrochemical systems by means of dynamic impedance spectroscopy. Electron transfer reactions across electrified interfaces involve a variety of processes, occurring at different time scales. A detailed understanding of the reaction kinetics requires the investigation of the system over a wide range of frequencies in order to capture all time constants related to the different underlying processes. In electrochemical impedance spectroscopy (EIS) a small-amplitude sinusoidal potential perturbation is imposed on the system by successively changing the frequency of the sinusoidal wave. The system's response to the perturbation signal provides an insight into the mechanism governing the reaction. EIS is a powerful tool that allows for the investigation of a variety of electrode processes in a single measurement. This method requires the stationarity of the system throughout the acquisition time of one full impedance spectrum. However, in many electrochemical systems a stable steady-state cannot be established, since the system undergoes irreversible changes during the measurement. Dynamic multi-frequency analysis (DMFA) uses a multi-sine waveform to apply all frequencies to the system simultaneously, thus allowing for the acquisition of impedance spectra in dynamic conditions. Here, DMFA is employed for the investigation of the nonstationary impedance behavior of different electrochemical systems, exhibiting either forced or natural reaction dynamics. Fundamental principles of data recording and analysis are examined by application of DMFA to a simple redox process. It is demonstrated that the temporal evolution of physical variables can be extracted from data analysis using suitable electrical equivalent circuits (EECs). Based on these results, different stages of the hydrogen evolution reaction (HER) are examined by means of DMFA. To do so, the system is subjected to forced dynamic conditions by combining quasi-$dc$ voltammetry and multi-sine impedance spectroscopy, thus providing a concatenated picture of the overall process. The investigation of the temporal evolution of the kinetic variables gives new insight into the mechanism of the HER. Finally, DMFA is employed for the examination of self-sustained current oscillations during the anodic electrodissolution of p-type silicon in fluoride containing electrolytes. The analysis of the system in dynamic equilibrium conditions provides the foundation for the investigation of the electrodissolution process in the oscillatory regime. DMFA allows for the characterization of different types of current oscillations in terms of their oscillatory reaction dynamics.Dissertation511 270