Trend-Workshop Hydrogen Technologies

As part of PSE 2024 in Erfurt last September, the "Hydrogen Technologies" trend workshop also took place and provided information on what coatings and surface technologies can contribute to the production and optimization of hydrogen technology components.

The main topics covered included

• Influence of economic and environmental aspects,
• Impact of different coating technologies,
• Regulations in the field of hydrogen applications,
• Classification in different application areas

Durable components are required to build a hydrogen infrastructure, and the climate-neutral element must also be obtained efficiently. What (Photo: stock.adobe.com/Planetz) thin-film and plasma technology can achieve was discussed in ErfurtLukasGröner, Fraunhofer IWM, presented barrier coatings in his paper "Development of hydrogen barrier coatings and characterization methods thereof", which can be used to prevent hydrogen from diffusing into hydrogen technology materials, as this can have mechanical (embrittlement), electrical or chemical effects. In some cases, gold coatings are applied for protection, but this is expensive. As a cheaper alternative, the lecturer presented nitride or oxide layers that were applied to ferritic steel membranes by reactive RF sputtering and high-power impulse magnetron sputtering (HiPIMS). Using the example of aluminum oxide layers _AlOx, he was able to show that droplets caused by arc processes can be largely avoided by controlling the pulse length and the pulse current. Scanning electron microscopy (SEM) was used to determine the type of defects and their frequency as well as the temperature-dependent influence on the barrier effect. The effectiveness of the coatings was determined by comparison with an uncoated membrane. The work showed that the barrier effect is only slightly impaired by droplets. Further work should predict the influence of defects on the barrier effect more precisely.

"Enhancing hydrogen permeating barriers on low alloy C-steel through optimized DLC coatings by PECVD" was the topic of the presentation by Oihane Hernández-Rodríguez, Tekniker, Eibar, Spain. Problems arise during the storage and transportation of hydrogen, e.g. hydrogen diffusing into steel materials can lead to embrittlement. Barrier layers (e.g. diamond-like carbon; DLC) can prevent this. The lecturer provided information on the deposition and characterization of these coatings as well as electrochemical permeation tests to prove the barrier effect. A PECVD process was used to deposit a-C:H coatings with a hydrogen content of 30 to 40 percent. With layer thicknesses of 1 to 2 µm, dense layers could be achieved, even inside hydrogen gas-conducting pipes. Measurements were carried out in a Devanathan-Stachurski cell to determine the permeation rate of the various DLC layers. This can be used to investigate the permeation of hydrogen through metal sheets or membranes. The lecturer was able to show that the barrier effect increases with the layer thickness, but decreases as the hydrogen content of the layers increases. The optimum is to be determined in further work.

"Plasma-based industrial processes for production of green hydrogen" - Adam Obrusník, PlasmaSolve s.r.o., Brno, Czech Republic, gave an overview of plasma-assisted gas conversion, by means of which methane, which is even more harmful to the climate than_CO2, can be converted into "green" hydrogen, which has a wide range of applications. Plasma offers advantages compared to conventional thermal chemistry, energy costs could be reduced and conversion efficiency increased. Upscaling to industrial scale would also be easier. Supported by simulation, CVD, PVD and also atmospheric pressure processes can be optimized. It is not yet possible to say whether the process yield specified by thermodynamics can be achieved or exceeded by the catalyst effect.

The hydrogen workshop was well attended (Photo: EFDS)

"_Cu2O/MoS2 electrodes produced by magnetron sputtering for water electrolysis" was the topic of Diogo Cavaleiro, University of Coimbra, Portugal. Electrodes produced by sputtering for water electrolysis do not require solvents, can be produced quickly and can be deposited on practically any substrate. MoS2 provides a high hydrogen yield in acidic solutions, which is not the case in alkaline solutions. In contrast, _Cu2Ois well suited to alkaline solutions. Two-phase electrodes as thin _Cu2O/MoS2layers can therefore greatly improve electrocatalytic performance. They were deposited by magnetron sputtering in oxygen/argon atmosphere with a _MoS2 and a copper target on different substrates (copper, silicone or gas diffusion electrodes). To optimize the interface between the two phases and increase the hydrogen yield, zigzag morphologies were generated by varying the angle of incidence. The electrodes exhibited high electrochemical activity, which is to be further increased by using new nanomanufacturing processes.

"Challenge accepted - High volume coating of metallic plates for hydrogen applications by PVD technology" - Philipp Immich, IHI Hauzer Techno Coating B.V., Venlo, Netherlands, presented the activities of his company. IHI Hauzer has been developing PVD coatings for many years and offers both system technology and coating services in cooperation with Ionbond. Key components of electrolyzers and fuel cells such as bipolar plates, porous transport layers (PTL sheets) or catalyst coated membranes (CCMs) require high-quality coatings with a good catalytic effect, high electrical conductivity and good corrosion resistance. Hauzer has developed PVD-based coatings for bipolar plates and PTL sheets and also provides the system technology required for their deposition. This should enable cycle times of one minute and annual throughputs of eight to ten million units. Corresponding precious metal-free coating systems have already been developed and are available for fuel cells. The focus here is on corrosion resistance and low electrical resistance with a lower overall layer thickness. Bipolar plates made of stainless steel can also be coated with titanium and then a carbon-based (DLC) layer. The current development focus in the field of electrolysis applications is on precious metal-reduced or even precious metal-free coatings (replacement of gold/platinum).

"In-situ testing of hollow specimens under _H2 atmosphere" - Dr. Bernd Schrittesser, SCIOFLEX Hydrogen GmbH, 7210 Mattersburg, Austria, provided information on this topic. Hydrogen can contribute to achieving the climate targets set by the EU. This makes it necessary to provide and improve the necessary processes and materials. For example, hydrogen embrittlement of steels can occur under the temperature and pressure conditions during the transportation of hydrogen. Tests are required to select materials compatible with hydrogen. The SSRT (slow strain rate tensile test) has so far been used to determine the influence of hydrogen on tensile strength. However, it is complex and cannot always be used. The lecturer presented a new test method that works with a special metallic hollow test specimen that is tested in an autoclave. This eliminates the need for conventional test methods. The advantages are faster and reproducible results, low hydrogen consumption and safe and cost-effective measurements.

Philippe Roquiny, AGC Plasma Technology Solutions - Gosselies, Belgium & Lauenförde, Germany -, presented in his lecture "_CH4 direct conversion in double vortex gliding arc reactor evaluation for green chemistry upscaling" a test facility developed at AGC for the conversion of_CO2 or _CH4 by means of plasmalysis. The experimental plant can process 50 liters of gas per minute, and the resulting end products are analyzed using sensors or gas chromatography. In contrast to_CO2 conversion, the process of converting CH4 is still unstable. The reason for this lies in the different heat capacity of_CO2 and _CH4, which could be explained with a digital twin. Further investigations are planned.