New stainless steel boosts green hydrogen production

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.

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.

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.

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.

Stainless steel is critical material used in a wide variety of industries. Unfortunately, current development of stainless steel has reached a stagnant stage due to the fundamental limitation of the conventional Cr-based single-passivation mechanism. Here, we show that, by using a sequential dual-passivation mechanism, substantially enhanced anti-corrosion properties can be achieved in Mn-contained stainless steel, with a high breakdown potential of ∼1700 mV (saturated calomel electrode, SCE) in a 3.5 wt% NaCl solution. Specifically, the conventional Cr-based and counter-intuitive Mn-based passivation is sequentially activated during potentiodynamic polarization. The Cr-based passive layer prevents corrosion at low potentials below ∼720 mV(SCE), while the Mn-based passive layer resists corrosion at high potentials up to ∼1700 mV(SCE). The present “sequential dual-passivation” strategy enlarges the passive region of stainless steel to high potentials above water oxidation, enabling them as potential anodic materials for green hydrogen production via water electrolysis.