Coatings in hydrogen transfer – material technology solutions to energy challenges

Hydrogen is a key component of the green energy system of the future. Hydrogen provides a clean and versatile energy source. Its use does not produce carbon dioxide emissions, and it can be produced using renewable energy sources such as solar and wind power. In addition, hydrogen can be used for energy storage, heavy transport, and industry, where electricity is not always a practical option. However, its production, storage, and transport require new technological solutions, particularly from the perspective of materials technology. For example, the use of green hydrogen produced by wind power in the chemical industry and energy production requires an extensive transport infrastructure. According to the European Hydrogen Backbone initiative, approximately 50,000 km of hydrogen pipelines are planned for Europe by 2040, with an investment need of €54–69 billion in pipelines, storage, and transport infrastructure (Hydrogen Europe, 2024).

Properties of hydrogen and transmission challenges

The transmission of hydrogen poses significant challenges. Hydrogen is a small-molecule, rare gas, and its transmission causes greater losses than, for example, the transmission of methane – approximately 15% more (Hora et al., 2024). In addition, the production and conversion of hydrogen back into energy is only about 46% efficient (Hora et al., 2024). Hydrogen embrittlement, leakage risks, and explosion sensitivity are particularly pronounced in enclosed spaces (Giannini et al., 2024). These safety considerations must be taken into account when designing hydrogen pipelines. As a small molecule, hydrogen has a higher flow velocity than methane, which increases friction losses. The roughness of the inner surface of the pipe, temperature, and pressure have a significant impact on transmission losses (Hora et al., 2024), and to reduce transmission losses, the inner surface of a hydrogen pipe must be smoother than that of a conventional natural gas pipe. The use of higher transfer pressures reduces pipeline losses. On the other hand, the use of higher pressures heats the gas and increases its density, which in turn increases pipeline losses. Finding the optimal operating conditions is therefore essential if and when pipeline losses are to be minimized. Naturally, it is clearly easier to design and manufacture hydrogen pipelines separately than to utilize old natural gas pipelines.

As a small and fast-moving molecule, hydrogen easily penetrates materials. Hydrogen is also chemically very reactive and causes a loss of strength in materials, making high-strength structural steels particularly brittle. The mechanisms of hydrogen embrittlement can be studied in more detail, for example, in the review article by Giannini et al. (2024). The choice of materials therefore plays an essential role in preventing hydrogen embrittlement. For example, L485 steel used in natural gas pipelines and AISI 316L stainless and acid-resistant steel used in laboratory hydrogen piping differ significantly in their material properties. L485 is a low-alloy, strong, and easily machinable steel that is susceptible to hydrogen embrittlement (Ez-Zaki et al., 2020). AISI 316L, on the other hand, contains more chromium, nickel, and molybdenum, which improves its corrosion resistance (Smits Metal Centres, 2023; Sandia National Laboratories, 2005). Both workability and corrosion resistance are extremely important properties required of hydrogen pipelines. The susceptibility of steel to hydrogen embrittlement can be prevented by coating the material in such a way that hydrogen cannot penetrate it (Wetergrove et al., 2023).

Coatings that prevent hydrogen migration

Various coating techniques, such as physical vapor deposition (PVD) (Physical Vapor Deposition, PVD), chemical vapor deposition (CVD), and atomic layer deposition (ALD), as well as liquid phase methods such as Sol-Gel and electrolytic methods, offer solutions for preventing hydrogen embrittlement.

However, small holes (e.g., in the Sol-Gel method) and coating irregularities (a problem in many PVD methods) can weaken the protective effect of coatings produced by different methods. In addition, the high coating temperature of over 500 degrees Celsius used in many CVD processes, for example, causes phase changes in steel that affect its material and strength properties. Promising coating materials include oxides and nitrides and their various layer structures (Wetergrove et al., 2023).

Of the coating methods, ALD is particularly well suited for the controlled production of oxide coatings at low temperatures (Bull, 2021). ALD coatings are dense, uniformly thick, and free of pores even at thicknesses of a few tens of nanometers. The challenge with ALD is the slowness of the process. However, the method is highly scalable for large pieces and is particularly well suited for coating the inner surface of pipes. Coating is usually carried out in vacuum chambers and separate facilities. Coating old natural gas pipelines would therefore require the development of a new coating technique and the installation of coating equipment inside the pipelines. ALD as a coating method and its advantages and disadvantages compared to other coating methods are described in more detail in my Tech to the Future blog from 2019 (Alakoski, 2019).

gH2ADDVA project experiments

The gH2ADDVA research project, jointly funded by the EU and the Central Finland Regional Council and carried out by Jyväskylä University of Applied Sciences and the University of Jyväskylä, is developing solutions for hydrogen transport and material durability. The project has tested, among other things, ceramic Al₂O₃ and TiO₂ coatings grown on steel tensile test bars using the ALD method. The Al₂O₃ and TiO₂ oxide coatings were grown at a temperature below 200°C using a Beneq TFS 500 device. These oxides were selected because they are highly effective ALD processes and, based on the literature (Wetergrove et al, 2023), promising materials for hydrogen corrosion. These oxides were chosen because they are highly effective in ALD processes and, based on the literature (Wetergrove et al, 2023), are promising materials for preventing hydrogen embrittlement. The coating was designed to combat hydrogen embrittlement by preventing hydrogen from migrating from the acid into the steel. Al₂O₃ and TiO₂ are also highly resistant to dilute acids.
ALD-coated TiO2 (titanium dioxide) steel tensile test bars before acid exposure.

In the tests, coated and uncoated bars were exposed to dilute sulfuric acid (H₂SO₄) and their strength properties, particularly tensile strength, were tested using Jamk's Zwick 330 Red material testing laboratory equipment. Tensile strength indicates how much a material can be stretched before it breaks. When hydrogen penetrates the material, it embrittles it. A rod embrittled by hydrogen breaks with significantly less force than a rod that has not been exposed to hydrogen. When the material is subjected to stress, the embrittling effect of hydrogen typically worsens. To investigate this, some of the coated rods were pre-stressed to a certain fraction of the material's yield strength. Yield strength refers to the stress at which the material begins to yield and no longer recovers after the stress is removed. Based on the measurements, the coating appears to protect the rod from the effects of acid and hydrogen in unstressed rods. This protective effect was not observed in stressed rods. The obvious reason for this is the difference in the strength properties of steel and the coating. Oxide coatings are ceramics, which are hard but brittle and can only withstand a small amount of strain without breaking. Steels can withstand more strain. When steel stretches, the ceramic coating gives way and breaks down.

Testing in dilute acid is a simple method used in many laboratories to test the material-technical effects of hydrogen exposure. A test method that better models the real situation would be hydrogen exposure at high pressure. Such testing equipment has been designed during the project and is currently under construction. The equipment is expected to be ready for laboratory testing in the final phase of the project.

The University of Jyväskylä is focusing on the development of hydrogen measurement methods in the project. Hydrogen is the lightest and smallest element, so it can easily move within a material and even escape from it. Measuring the concentration (amount) of hydrogen in a material is therefore challenging, and the development of measurement methods is also valuable from a scientific research perspective. The Department of Physics at the University of Jyväskylä uses a particle accelerator for its measurements, and the TOF-ERDA method is particularly well suited for measuring hydrogen. In this method, the surface of the sample being studied is bombarded at a shallow angle with high-mass ions, i.e., electrically charged atoms. The ions are produced in an ion source using voltage and accelerated towards the target with a voltage of millions of volts. The largest "projectiles" kick out smaller atoms, such as hydrogen, from the sample in collisions comparable to the ricocheting of billiard balls. The high-mass "projectiles" knock smaller atoms, such as hydrogen, out of the sample in collisions comparable to the ricochet of billiard balls. In the TOF-ERDA method, both the mass and energy of the atoms ejected from the sample into the detector can be measured, and even the amounts of different hydrogen isotopes can be distinguished (Kinnunen et al. 2021). Hydrogen isotopes include normal hydrogen, which has one proton in its nucleus, deuterium, which has one neutron in addition to a proton in its nucleus, and radioactive tritium, which has two neutrons in addition to a proton in its nucleus. The TOF-ERDA measurements in the project have shown that hydrogen has migrated from oxygen made from heavy water into L485 steel. Normal hydrogen can also migrate into the sample from elsewhere in the environment. In heavy water, hydrogen has been replaced by deuterium. When a deuterium signal (concentration) is measured in the sample, it can be confirmed that the hydrogen originates from the acid. Next, the possibility of limiting hydrogen migration and preventing hydrogen embrittlement with ALD coatings will be investigated.

The University of Jyväskylä is also investigating the possibility of using X-ray tomography to image material damage caused by hydrogen embrittlement. In this method, two-dimensional X-ray images are taken of the objects and the images are combined into a 3D image and model using a computer. Tomography imaging is typically used in medicine to image organic matter and tissues. The density of ordinary tomography samples is low compared to the density of steel. The high density of steel is a challenge when it comes to imaging the effects of hydrogen embrittlement. If you want to image precise details inside a steel sample, you need a high-power X-ray source. With the university's equipment, the power requirement limits the sample size to a fraction of the thickness of a hair. For imaging purposes, steel wire with a diameter of a few tens of micrometers has been purchased. Such wire is barely visible to the naked eye and is extremely challenging to handle. Nevertheless, the first tomography images of the wire have been obtained. In the final phase of the project, the aim is to further develop the method and image steel wire exposed to hydrogen.

Summary and conclusions

Hydrogen will play a significant role as an energy carrier in the fossil-free energy system of the future. However, hydrogen must be able to be transported over long distances. The development of the pipelines and other infrastructure needed to transport hydrogen is challenged by material engineering problems caused by hydrogen, such as hydrogen embrittlement. The joint gH2ADDVA project between the University of Jyväskylä and Jyväskylä University of Applied Sciences is developing hydrogen measurement techniques for researching hydrogen and its material engineering effects, as well as coating solutions for the challenges of hydrogen transport. Various coating methods can be used to prevent hydrogen embrittlement by blocking the passage of hydrogen into the pipe steel. Oxide coatings produced using the ALD method are particularly promising. ALD coatings are dense, uniformly thick, and impervious even at a thickness of just a few tens of nanometers. This method makes it possible to coat even large pipes with a uniformly thick, dense coating. Coating is a particularly promising solution for new transfer pipelines, which can be coated before installation. Coating existing natural gas pipelines requires coating equipment to be inserted into the pipeline and a new type of coating technology.

The article was originally published on 4 December 2025 in the online magazine Jamk Arena Pro under a CC BY licence and is available at https://urn.fi/urn:nbn:fi:jamk-issn-2984-0783-267.