Stainless steel can be used in a number of hydrogen production techniques, especially those that involve steam methane reforming and electrolysis.

In terms of steam methane reforming, the material is used in the construction of reformers, heat exchangers, and other components of the process as it is particularly well-suited to withstand high temperatures and corrosive environments.

In terms of water electrolysis, the material is often used in the construction of electrolyzers due to its corrosion resistance and durability in the process’ harsh electrolytic environment.

Green hydrogen from our oceans

Now, a new initiative spearheaded by Professor Mingxin Huang at the Department of Mechanical Engineering of the University of Hong Kong (HKU) has created a novel kind of steel with strong resistance to corrosion that may be used in the manufacture of green hydrogen from saltwater easily acquired from our oceans.

While the cost of the new steel is far lower than its corresponding current counterparts, its performance in a saltwater electrolyzer is equivalent to the present industrial practice of employing titanium as a key structural part to create hydrogen from desalted seawater or acid.

The invention consists of adding a secondary manganese (Mn)-based layer engineered on the preceding chromium (Cr)-based layer at ~720 mV onto the single Cr2O3-based passive layer. Because the general consensus is that Mn reduces stainless steel's ability to withstand corrosion, the scientists did not first accept the material’s new role. This is because the discovery of Mn-based passivation is counterintuitive and defies conventional corrosion science understanding.

“However, when numerous atomic-level results were presented, we were convinced. Beyond being surprised, we cannot wait to exploit the mechanism,” said Dr Kaiping Yu, the first author of the article, whose PhD is supervised by Professor Huang.

Reducing the cost of production by 40 times

At present, the total cost of a 10-megawatt PEM electrolysis tank system is estimated to be HK$17.8 million (USD $ 2.8 million), of which up to 53 percent is attributed to the structural components. Thanks to the innovation of Huang's group, steel may now be used in place of traditional pricey structural elements such as gold (Au) and platinum (Pt). According to estimates, stainless steel for hydrogen (SS-H2) will reduce structural material costs by approximately 40 times.

“From experimental materials to real products, such as meshes and foams, for water electrolysers, there are still challenging tasks at hand. Currently, we have made a big step toward industrialisation. Tons of SS-H2-based wire has been produced in collaboration with a factory from the Mainland. We are moving forward in applying the more economical SS-H2 in hydrogen production from renewable sources,” explained Huang.

The researcher’s team is also behind the development of anti-COVID-19 stainless steel first introduced in 2021, and ultra-strong and ultra-tough Super Steel engineered in 2017 and 2020 respectively.

The study is published in the journal Materials Today.