Most of the hydrogen produced today is made using fossil fuels, making a significant contribution to global CO2 emissions. Although polymer electrolyte membrane water-electrolyzers can produce green hydrogen by means of excess electricity generated from renewable energy sources, their operation is still not economical. According to industry experts, the necessary cost reductions can be achieved by 2030 if system efficiency can be improved. The commonly stated idea is to improve efficiency by increasing the stack temperature, which requires the development of more resistant materials. This study investigates not only the efficiency of an electrolysis cell, but of the entire electrolysis process, including gas compression of hydrogen. The results indicate that an optimal stack temperature exists for every operating point. It is shown that the optimal temperature depends solely on the electrode pressure and cell voltage and can be analytically calculated. In addition, the temperature optimization leads to significantly reduced hydrogen permeation at low current densities. In combination with the pressure optimization, the challenging safety issues of pressurized electrolysis can be eliminated for the entire load range and, at the same time, the efficiency of the overall system be maximized.

As a future fuel hydrogen should be stored at elevated pressure because of its low volumetric energy density. For transport in pipelines, a suitable pressure is about 200 bar. There are different paths conceivable to achieve this storage pressure. As an alternative to the conventional way of compressing the gas in external compressors subsequently, it is frequently discussed to operate electrolyzers at elevated pressure, which can save costly compressor stages. High Faraday efficiencies will be achieved by using improved materials with low permeation rates or thick membranes. However, thick membranes worsen the system performance since the decreased protonic conductivity of the cells ultimately reduces the amount of hydrogen produced. Therefore, it is recommendable to take a closer look at this context and to evaluate an optimized pressure operation depending on the application and cell parameters. In a comprehensive analytical model approach we discuss how voltage efficiency, Faraday efficiency and energy required for external gas compression are affected by a various number of system parameters. We demonstrate that the optimum gas pressure in electrolyzers is not only a function of the membrane thickness but strongly depends on the entire system configuration. To answer the question of whether high-pressure polymer electrolyte membrane electrolyzers are worthwhile both energetically and economically, our model was fed with a typical parameter set for systems based on Nafion 212 and Nafion 117. Our results demonstrate impressively why the use of thin membranes and their future development are a must for the meaningful use of PEM water electrolysis in a future energy grid.

In order to reach the system efficiency targets for PEM water electrolysis of more than 70%LHV at current densities of up to 3 A/cm², thin membranes are indispensable. It is known that the use of thin membranes leads to the disadvantage that they additionally have to be stabilized mechanically and chemically for cell operation. Furthermore, it is known that during pressure operation, a large amount of gas permeates through the thin membrane. This can result in forming explosive gas mixtures of oxygen and hydrogen at the anode, especially at low current densities, which prevents a safe electrolysis operation. However, little research has been done so far that, when using thin membranes, additional effects can arise which significantly increase the gas permeation. These effects lead to safety-relevant hydrogen concentrations at the anode, not only for small but also for larger current densities of a few amperes per square centimeter. It is demonstrated that, without an intensive comparison of material and cell operating parameters, a comparison of different investigations with respect to the measured permeation values in PEM water electrolysis can hardly be made. Important parameters are discussed which have to be taken into account in cell assemblies when thin membranes are used. The presented experimental results show a correlation in the PEM water electrolysis MEA which can significantly increase the hydrogen permeation through a 50 μm thin N212 membrane under ambient pressure. At the same time, it is demonstrated how the hydrogen content in the anode gas can be reduced to very low levels using the identified correlation.

During film fabrication, the phenomena of crack formation and delamination are often observed, dramatically hindering the discovery and characterization of new materials for energy applications. In this work, we report on a novel approach to fully steer the drying parameters or “knobs” that are commonly used during electrode manufacture. It allows us to precisely in situ control and monitor the solvent-specific evaporation rates that affect the development of suspension composition during drying. We managed to control the capillary stress inside the layer by precisely controlling the selectivity of solvent evaporation. Large cracks result when the surface tension increases over time and layer delamination occurs. When using an n -propanol/water system, critical crack formation is achieved when water is enriched by decreasing the gas exchange during drying or preloading the gas phase with water vapor. High gas exchange rates inhibit the water’s enrichment, and therefore, only small surface cracks develop. The experiments also surprisingly indicate that the drying temperature has no significant effect on crack formation. These results are of fundamental meaning for the future development of electrodes as the drying step has a high impact on the products specification and now can be ultimately controlled. The future development of electrodes will surely benefit from this achievement in the controlled fabrication of films for a variety of applications.

The future of energy conversion and storage is expected to rely on the production and storage of hydrogen using water electrolyzers. In this scenario, water electrolyzers will play a key role in the establishment of an energy matrix based on renewable but intermittent power sources (e.g. wind turbines and photovoltaics). Hydrogen has the potential to drive multiple revenue streams like transportation, chemicals, green production of fertilizers, regeneration of electricity through fuel cells, and also initially supplement the energy gap through methanation. Moreover, the production, storage, or distribution can be chosen to be centralized or decentralized, and is recognized as the only option to store multi-GWh electricity. 1 In order to meet the future demand for water electrolyzers, investment and operational costs still have to be reduced. It is also crucial to develop electrolyzers that are able to operate at high current densities, variable partial load, overload, and on/off conditions. These requirements usually place PEM water electrolysis as an optimal alternative to couple with intermittent power sources. In any case the high costs of PEM water electrolysis components (based on Pt, Ir, and Ti components) are still hampering its large-scale commercial application. 2 Though consistent R&D we aim to drastically reduce the costs and increase the efficiency of PEM water electrolyzers. By using advanced methods to design and characterize nanostructures and catalyst coated membranes, and by properly accessing the performance and durability of cell and stack components, we hope to be able to demonstrate in the next years the next generation of PEM water electrolyzers, and its future incorporation into our energy matrix for energy storage and conversion.

Electrodes for polymer electrolyte membrane electrolyzers and fuel cells are manufactured by coating a catalyst dispersion, consisting of precious metal, ionomer and solvents, onto a substrate that is subsequently dried. One target of current research is to produce square meter-sized electrodes, but so far the homogeneity that can be achieved in this scaling is unclear. To quantify the achievable homogeneity of an electrode, manufactured by means of slot die coating in a roll-to-roll pilot plant, this study focuses first on the selection of an appropriate substrate by investigating thickness, basis weight and surface free energy distribution at the square meter scale. Afterward, a dispersion is coated on the selected substrate, dried and investigated with respect to thickness and basis weight distribution. Among the investigated substrates, Kapton has the smallest scatter in terms of thickness and basis weight. The subsequent coating results in a precious metal loading of 1.10 mg cm\(^{-2}\), with a scattering of 5.5% that can be further reduced to 4.5% when edge effects can be prevented. These results are now available for further research in which it is necessary to investigate whether or not these fluctuations affect the achievable electrochemical efficiencies of electrodes.

The establishment of a fully renewable energy system is predicated on the use of hydrogen as a fuel. Polymer electrolyte membrane (PEM-) water electrolyzers for its generation and (PEM-) fuel cells for its reconversion will be essential components of such a system. In order for this to be economically feasible, however, their costs have to be reduced. The quantity of expensive materials utilized for the construction of cells, including platinum, iridium or titanium must be reduced and overall efficiency increased. The efficiency of these devices is a function of the electrochemical processes that take place in the electrodes and is inseparably tied to their structure. The structure can be affected by controlling various steps in the manufacturing progress. Aside from the chemical composition of the wet coat (consisting of the supported catalyst, Nafion®, solvents and additives) the drying plays a significant role during the self-organization progress in the catalyst layer. Therefore, the drying aspect is one of the main focuses of interest. Nowadays the most commonly used catalyst-containing dispersions in the manufacturing of membrane electrode assemblies (MEAs) are based on a mixture of organic solvents. In order to clarify the drying process a test rig was constructed. By using a gas phase infrared spectrometer the drying can be monitored by analyzing the waste gas. The set up enables a wide range of conditions in terms of the temperature and the type of drying gas and its preloading. Furthermore, the contact time between the drying gases with the coated layer is adjustable. As various substances differ in their boiling points a different drying rate is observed for each organic component inside the electrode layer. Consequently, the physical and chemical parameters of the solvent mixture which evaporates during the drying step change dramatically over time. The test rig gives time-resolved information about the selectivity of drying, and the drying rates of the single mixture components in general. The measurement system provides accurate and consistent results. The low measurement uncertainty (< 2% rel.) offers an ideal tool for observing slight modifications during the drying progress.

In the construction of polymer electrolyte membrane fuel cells (PEMFCs) and polymer electrolyte membrane electrolyzers (PEMELs), Nafion® (sulfonated tetrafluorethylene) is used as a membrane material and as proton conductor in the porous catalysts layers of membrane electrode assemblies (MEAs). Efficiency can be increased and costs reduced by optimizing and controlling the porous catalyst layer in MEAs. It is important to understand the polymer properties, which can be achieved by using different solutions and varying concentrations of one mixture for manufacturing the dispersion. Furthermore, the findings are of particular importance for the coating process. The efficiency of the PEMFCs and PEMELs depends on the number of active centers in the porous catalyst layer. The formation of the triple phase boundary is of great importance. This can be ensured by controlling the structural properties of the dispersion. Thereby, the static and dynamic surface tensions are analyzed. Surface tension and interfacial tension are necessary for understanding the coating process and adhesion to a transfer layer. The complex system was simplified and research on the surface properties performed with an aqueous Nafion® solution in an alcohol concentration series. Hence, the only aspect that changed was the alcohol, while the dynamic surface tension was measured with a bubble pressuretensiometer (BP100, KRÜSS GmbH). The static surface tension and interfacial surface tension were carried out with a force tensiometer (K100, KRÜSS GmbH) after Wilhelmy plate respectively the duNouy Ring method. In addition the solution was analyzed by means of IR- and 19F-NMR- spectroscopy. It will be demonstrated in this contribution that the static and dynamic surface tensions differ significantly at lower alcohol concentrations in solution series with and without Nafion®. While at higher alcohol concentrations the static surface tension between both series is similar, the dynamic surface tension shows a different trend with varied bubble age. This can be explained by the interaction between alcohol and Nafion®. In accordance with the previous interface outcomes, the 19F-NMR- and IR- spectra are analyzed. According to the first results, it is also apparent that there are interactions between Nafion® and alcohol. The application of these methods provides an understanding of the interaction between the molecules in the catalyst dispersions. This information is essential for understanding the interactions between the components of catalyst dispersion during electrode manufacturing.