This study introduces analyzes a slow-growing degradation effect that can occur when using thin catalyst-coated membranes for PEM water electrolysis. The electric current through a test cell increased during experiments in potentiostatic operation, but the oxygen evolution rate contradicted Faraday's law. Impedance measurements below the decomposition voltage of water at the beginning and end of the experiment revealed that a new electrical phase boundary (semicircle in the Gaussian plane) arose. This allows electrons to flow across this phase boundary without triggering electrochemical reactions. SEM/EDX cross-sectional analyses show the formation of globular iridium clusters within the membrane, which grow from the anode through the membrane to the cathode. These clusters, whose formation is not yet understood, are most likely responsible for the formation of slowly-increasing short circuits between the electrodes.

Green hydrogen is a key solution for reducing CO2 emissions in various industrial applications, but high production costs continue to hinder its market penetration today. Better competitiveness is linked to lower investment costs and higher efficiency of the conversion technologies, among which polymer electrolyte membrane electrolysis seems to be attractive. Although new manufacturing techniques and materials can help achieve these goals, a less frequently investigated approach is the optimization of the design point and operating strategy of electrolyzers. This means in particular that the questions of how often a system should be operated and which cell voltage should be applied must be answered. As existing techno-economic models feature gaps, which means that these questions cannot be adequately answered, a modified model is introduced here. In this model, different technical parameters are implemented and correlated to each other in order to simulate the lowest possible levelized cost of hydrogen and extract the required designs and strategies from this. In each case investigated, the recommended cost-based cell voltage that should be applied to the system is surprisingly low compared to the assumptions made in previous publications. Depending on the case, the cell voltage is in a range between 1.6 V and 1.8 V, with an annual operation of 2000-8000 h. The wide range of results clearly indicate how individual the design and operation must be, but with efficiency gains of several percent, the effect of optimization will be indispensable in the future. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

The design and operation of electrolyzers are always a trade-off between parameters that contrarily affect performance and operational goals. This talk will discuss some of those. Compression of the product gases within an electrochemical process is often discussed as an alternative to subsequent mechanical compression. On the one hand, the electrochemical compression is advantageous in terms of energy efficiency; on the other hand, elevated gas pressure is responsible for increased gas loss due to permeation across the membrane. This can be prevented by using thicker membranes; in return, it impairs the proton transport in the electrolyzer and ultimately reduces its performance. It is therefore advisable to discuss an energetically sensible gas pressure level. As gas permeation is a crucial impact on this trade-off, it needs to be discussed how it is affected through operating conditions. Aside from the gas pressure difference between anode and cathode, the diffusion rate increases exponentially with temperature. However, lowering the stack temperature diminishes the electrochemical reaction kinetics as well as the ion conductivity of the ionomer. Hence, the influence of gas pressure, stack temperature and polarization curves on the plant efficiency are inextricably linked. Simulation results indicate that the energetically optimal design and operating conditions are functions of the applied cell voltage. As the design of the electrolysis plant is determined by its installation, only the operating conditions can be chosen flexibly. Economically, investment costs are best allocated to the cost of hydrogen when using high current density in order to have a high production capacity. On the contrary, a high current density also means a high cell voltage, which in turn results in a low plant efficiency and is responsible for high operating costs. Considering all these effects, the complexity of dependencies between parameters will be illustrated in this talk and how modeling can be used to access them. The results will outline challenges as well as directions how the technology can be further developed in future. Figure 1

In the future, hydrogen (H2) will play a significant role in the sustainable supply of energy and raw materials to various sectors. Therefore, the electrolysis of water required for industrial-scale H2 production represents a key component in the generation of renewable electricity. Within the scope of fundamental research work on cell components for polymer electrolyte membrane (PEM) electrolyzers and application-oriented living labs, an MW electrolysis system was used to further improve industrial-scale electrolysis technology in terms of its basic structure and systems-related integration. The planning of this work, as well as the analytical and technical approaches taken, along with the essential results of research and development are presented herein. The focus of this study is the test facility for a megawatt PEM electrolysis stack with the presentation of the design, processing, and assembly of the main components of the facility and stack.

Gas permeation through a membrane electrode assembly (MEA) is an important issue in the development of polymer electrolyte membrane (PEM) water electrolyzers, because it can cause explosions and efficiency losses. The influence of operating pressure, temperature and MEA modifications on the permeation was already investigated. However, most of the studies pay no attention to the compression of the porous transport layer (PTL) of the MEA when assembling it in a test cell to carry out the experiments. This paper deals with the impact of the PTL compression on hydrogen permeation and cell voltage. Polarization, impedance and permeation measurements are used to demonstrate that the compression significantly affects the MEA's properties. Measurements show either a linear or nonlinear correlation between current density and hydrogen permeation, depending on the compression. The results indicate that the compression of the PTL must be taken into account for developing MEAs and comparing different permeation measurements. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

This work shows how to manufacture completely coated membrane electrode assemblies (CC-MEAs) for PEM water electrolysis by only using a slot die. Platinum, Nafion (R), and IrO2 dispersions are successively coated to the respective dried layer. For comparison reasons, MEAs with the same Iridium loading of 2.1 mg cm(-2) and Platinum loading of 0.4 mg cm(-2), assembled with a commercial membrane of the same 20 mu m thickness, were produced via decal method. Differences in polarization curves are attributed to the lower high frequency resistance of CC-MEAs determined by impedance spectroscopy. The easy-to-scale CC-MEA method presented here offers the advantages of direct membrane deposition (DMD) without the challenge of homogenously coating a porous transport layer (PTL). Therefore, it allows a free choice of different PTLs - regardless if in sintered form or as expanded metal. The comparability between the produced CC-MEAs and published DMD results is shown by means of cross-sectional and electrochemical measurements. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Polar and dispersion surface free energy (SFE) can be determined with the Owens-Wendt method. Thereby, contact angles (CAs) of at least two liquids with known surface tension (ST) components are measured. The ST components can either be determined through experiment or drawn from literature. However, it is important to know how big the difference is between SFE component values that have been calculated with experimentally-determined ST values or values derived from literature. In this study, STs of different test liquids were analyzed by Pendant Drop method and the components by CA measurement on a non-polar surface. CAs on different polymer surfaces were measured to calculate SFE components with the Owens-Wendt method. The calculations conducted were either based on experimentally-determined ST parts or different sets of values found in the literature. The findings of the survey show that, depending on the set of literature values used, the SFE results deviate significantly from the values obtained from experiment. Expressing this deviation in figures, in extreme cases the polar part differs for some polymers by -100% to +100%, with the dispersion component spanning -50% to +43%. In comparison, the expected relative uncertainties exhibited by the experimentally-determined ST values are about 15% for the polar and approximately 5% for the dispersion SFE part. Hence, the results show that the SFE uncertainty can be reduced significantly by means of analyzing the ST parts experimentally.

It has been well-established that effects such as cracking are observable when wet layers are dried. In particular, the layer thickness, as well as the surface tension of the liquid, is responsible for this behavior. The layer formation of polymer electrolyte fuel cells and electrolyzer electrodes, however, has not yet been analyzed in relation to these issues, even though the effect of cracks on cell performance and durability has been frequently discussed. In this paper, water propanol polymer-containing carbon-black dispersions are analyzed in situ with regard to their composition during drying. We demonstrate that crack behavior can be steered by slight variations in the initial dispersion when the solvent mixture is near the dynamic azeotropic point. This minor adjustment may strongly affect the drying behavior, leading to either propanol or water-enriched liquid phases at the end of the drying process. If the evaporation of the solvent results in propanol enrichment, the critical layer thickness at which cracks occur will be increased by about 30% due to a decrease in the capillary pressure. Microscopic images indicate that the crack area ratio and width depend on the wet layer thickness and initial liquid phase composition. These results are of much value for future electrode fabrication, as cracks affect electrode properties.