Boris Bensmann

Nonlinear Frequency Response of Electrochemical Methanol Oxidation Kinetics: A Theoretical Analysis

In this theoretical contribution, nonlinear frequency response analysis was applied for the investigation of electrochemical methanol oxidation. This technique expresses the input-output behavior of any weakly nonlinear system with the help of the Volterra series expansion and generalized Fourier transform into so-called higher order frequency response functions. These functions contain the systems nonlinear fingerprint. They can be derived analytically from a nonlinear model. These functions can be obtained experimentally from the measurement of higher harmonics induced by a high amplitude sinusoidal perturbation of the system of interest. Frequency response functions up to the second order have been derived analytically for four different model varieties describing the kinetics of the electrochemical methanol oxidation. The first-order frequency response function corresponds to the reciprocal value of the well-known electrochemical impedance, which represents the linear part of the frequency response. This function does not contain sufficient information for discrimination between the different kinetic models. In contrast, the symmetrical second-order frequency response functions H 2 (ω,ω) show differences in shape, which substantiate the availability of the theoretical prerequisites for model discrimination. A detailed parametric study for all four model variants has been performed. The results show that the basic features of the shapes of the H 2 (ω,ω) amplitude spectra corresponding to the four models remain unique. The ubiquitousness of the qualitative differences between the competing models, for the whole set of parameters chosen for our analysis, suggests that the aforementioned amplitude spectra contain sufficient information for an unequivocal model discrimination.

Anodic microporous layer for polymer electrolyte membrane water electrolysers

A microporous layer represents an important element of the gas diffusion electrodes used in polymer electrolyte membrane (PEM) fuel cells and water electrolysers. It forms an interface between the nanostructured catalyst layer and the macrostructured electrode body. In the case of PEM water electrolysis such a layer has only been applied to the cathode to date. On the other hand, it is typically absent on the anode side of the cell. In the present study, such a layer was integrated into the anode of a PEM water electrolyser. It was based on antimony-doped tin oxide placed on titanium felt forming the electrode backing. Using an in-house synthesised IrO2, gas diffusion anodes were manufactured with and without the microporous layer and their performance compared in a laboratory PEM water electrolyser. Current–voltage curves and electrochemical impedance spectra were recorded. The results revealed that the microporous layer is only advantageous in a range of low current densities, while at higher current densities the ohmic resistance of the microporous layer significantly reduces the efficiency of electrolysis.Graphical Abstract

Model simulation and analysis of proton incorporation into the positive active mass of a lead/acid battery: influence of transient and steady-state behavior

In this theoretical work, a mathematical model of the positive active mass of a lead/acid battery considering the effect of proton incorporation into the solid material of the lead dioxide electrode is presented. It can be regarded as an extension of a classic isothermal description, well known from literature. The influence of the proton incorporation reaction on the transient behavior as well as on the steady-state profiles has been analyzed and compared to the classical model. A significant influence of the process of proton incorporation on the transients of the model quantities was found, which reflects a pseudocapacitive behavior of the positive active material. This effect stabilizes the positive electrode potential, especially at a short-time high rate current flow. It could be shown that the transport of protons through the active mass is also present in steady-state conditions. This allows the protons two alternative ways of transportation, liquid and solid phases, in both transient and steady-state situations. Proton transport in the solid phase has not been considered before and may explain the high pseudocapacity of lead dioxide positive active material.

Effect of the MEA design on the performance of PEMWE single cells with different sizes

In the field of polymer electrolyte membrane water electrolysis (PEMWE), a significant amount of excellent scientific results has been generated during the past decades. However, the comparability and reproducibility of these results between different cell types and different laboratories is not always straightforward. In this contribution, an exemplary ring experiment on the single-cell level compares the performances of three cell types: the differential cell (

Optimal configuration and pressure levels of electrolyzer plants in context of power-to-gas applications

{4}{\text { cm}^{2}}

Current density effect on hydrogen permeation in PEM water electrolyzers

4cm2) and two integral cells: an elongated cell (

Conceptual design of operation strategies for hybrid electric aircraft

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