A team led by Professor Minxin Huang from the Department of Mechanical Engineering at the University of Hong Kong has made significant advances in the field of stainless steel. This latest innovation focuses on the development of hydrogen grade stainless steel known as SS-H.₂.

This achievement is part of Professor Huang’s ongoing Supersteel project; This project has previously made significant progress in the development of stainless steel for protection against COVID-19 in 2021 and in the development of ultra-high-strength and ultra-high-strength super steel in 2017 and 2020. .

The new steel developed by the team shows high corrosion resistance, allowing it to be potentially applied in the production of green hydrogen from seawater, where a new sustainable solution is still being developed.

The new steel’s performance in a brine electrolyzer is comparable to current industrial practice, where titanium is used as structural parts to produce hydrogen from desalinated seawater or acid, while the new steel costs much less.

The discovery was published in a journal Today’s Ingredients. The research advances are currently filed for patents in many countries, and two of them have already been granted.

Revolutionary resistance to corrosion

Stainless steel has always been an important material widely used in corrosive environments since its discovery a century ago. Chromium is an important element in determining the corrosion resistance of stainless steel. The passive film is formed by the oxidation of chromium (Cr) and protects stainless steel in the natural environment. Unfortunately, this common Cr-based one-time passivation mechanism has stalled the further development of stainless steel. Due to further oxidation of stable Cr₂HE₃ Based on the soluble forms of Cr(VI), transpassive corrosion inevitably occurs in conventional stainless steel at ~1000 mV (saturated calomel electrode, SCE); this is below the potential required for water oxidation at ~1600 mV.

For example, super stainless steel 254SMO is the benchmark among Cr-based anti-corrosion alloys and has excellent resistance to spot correction in seawater; however, transpassive corrosion limits its application at higher potentials.

Professor Huang’s research group developed a new SS-H using the “sequential pair passivation” strategy₂ It has excellent corrosion resistance. In addition to a Cr-based passive layer₂HE₃, the secondary Mn-based layer is formed on the previous Cr-based layer at ∼720 mV. Sequential double passivation mechanism prevents SS-H corrosion₂ In chloride environments up to ultra-high potential of 1700 mV. SS-H₂ It represents a fundamental breakthrough compared to traditional stainless steel.

Unexpected discoveries and potential applications

“At first we did not believe it because the prevailing opinion was that Mn worsens the corrosion resistance of stainless steel. Manganese-based passivation is a counterintuitive discovery that cannot be explained by the current knowledge in corrosion science. But when numerous results were presented at the atomic level, we were convinced. Besides being surprised, we were also surprised to use this mechanism We can’t wait,” said Dr. Kaiping Yu.

The team devoted nearly six years to their work, from the initial discovery of the innovative stainless steel to achieving a breakthrough in scientific understanding and ultimately preparing for formal publication and hopefully industrial application.

“Unlike the current corrosion community, which generally focuses on resistance to inherent potentials, we specialize in the development of alloys resistant to high potentials. Our strategy has overcome the fundamental limitations of conventional stainless steel and created a paradigm for the development of alloys suitable for high potentials. This breakthrough brings exciting and new applications. ” Professor Huang said.

Currently water electrolyzers in desalinated seawater or acidic solutions require expensive Au or Pt-coated Ti for structural components. For example, the total cost of a 10 MW PEM electrolysis tank system is currently approximately HK$17.8 million, with structural components accounting for 53% of the total cost. The discovery made by Professor Huang’s team makes it possible to replace these expensive structural components with more economical steel. It is estimated that SS-H was used.₂By introducing best practices in industrial applications, it is expected to reduce the cost of structural material by approximately 40 times.

“From experimental materials to real products such as meshes and foams for water electrolyzers, there are still challenges ahead. We have now taken a big step towards industrialization. Tons of SS-H2-based wires have been produced in cooperation with a factory on the mainland. We are moving forward with the more economical SS-H ₂ in the production of hydrogen from renewable sources,” added Professor Huang.