Hong Kong — 11 August 2026. A team at the University of Hong Kong (HKU) has developed a new type of stainless steel that withstands extreme seawater corrosion under conditions that destroy conventional stainless steel, potentially enabling dramatically cheaper green hydrogen production from seawater. The material, designated SS-H2 (stainless steel for hydrogen), uses a counter-intuitive manganese-based protective mechanism that the researchers themselves initially struggled to believe.
The findings, published in Materials Today, represent the latest advance from Professor Mingxin Huang's "Super Steel" Project, which previously produced anti-COVID stainless steel in 2021 and exceptionally strong and tough variants of super steel in 2017 and 2020.
The Fundamental Limitation of Conventional Stainless Steel
Stainless steel has been used for roughly a century and derives its corrosion resistance from chromium. When chromium reacts with the environment, it forms a thin passive film of chromium oxide (Cr₂O₃) on the surface, preventing further corrosion of the underlying metal.
This protection has a critical limit. At sufficiently high electrical potentials, the protective chromium oxide undergoes further oxidation to form soluble Cr(VI) species — a degradation process known as transpassive corrosion. For conventional stainless steels, this occurs at approximately 1000 mV (saturated calomel electrode, SCE).
The problem is that water oxidation — the essential reaction during electrolysis that splits water into hydrogen and oxygen — requires a substantially higher potential of approximately 1600 mV. This mismatch has prevented conventional stainless steel from being used effectively in high-voltage electrochemical applications, including seawater electrolysis for hydrogen production.
Even 254SMO super stainless steel, considered a benchmark chromium-based corrosion-resistant alloy with excellent resistance to pitting in seawater, faces this limitation. Its corrosion resistance decreases when the electrical potential becomes sufficiently high.
Sequential Dual-Passivation: A Surprising Second Layer
Huang's group overcome this limitation using what they call "sequential dual-passivation." Instead of relying solely on the traditional chromium oxide layer, SS-H2 develops a second protective layer on top of it. This second layer is based on manganese and begins forming at approximately 720 mV.
Together, the two layers allow the steel to resist corrosion in chloride-containing environments at potentials reaching 1700 mV — beyond the potential needed for water oxidation.
What makes the result striking is the role of manganese. Traditionally, manganese has been regarded as harmful to the corrosion resistance of stainless steel. The discovery that a manganese-based passivation layer could provide protection at high potentials overturns a long-standing assumption in corrosion science.
"Initially, we did not believe it because the prevailing view is that Mn impairs the corrosion resistance of stainless steel," said Dr. Kaiping Yu, first author of the study, whose PhD is supervised by Professor Huang. "Mn-based passivation is a counter-intuitive discovery, which cannot be explained by current knowledge in corrosion science. However, when numerous atomic-level results were presented, we were convinced. Beyond being surprised, we cannot wait to exploit the mechanism."
Performance in Seawater Electrolyzers
In a salt water electrolyzer, SS-H2 delivered performance comparable to titanium structural components currently used to produce hydrogen from desalinated seawater or acidic solutions. The critical difference is cost.
Electrolyzers operating with desalinated seawater or acidic solutions currently require expensive titanium components coated with gold or platinum. According to the researchers, a 10-megawatt PEM (proton exchange membrane) electrolysis tank system currently costs approximately HK$17.8 million, with structural components representing as much as 53% of the total system cost.
Six Years of Research
The project took nearly six years, beginning with the discovery of the unusual steel and continuing through efforts to understand why it behaved this way at the atomic level. Huang's group has focused on developing materials that remain stable at much higher electrical potentials than conventional corrosion science typically addresses.
"Different from the current corrosion community, which mainly focuses on the resistance at natural potentials, we specialize in developing high-potential-resistant alloys," said Professor Huang. "Our strategy overcame the fundamental limitation of conventional stainless steel and established a paradigm for alloy development applicable at high potentials. This breakthrough is exciting and brings new applications."
The researchers have applied for patents covering the technology in several countries, and two patents have already been authorized.
From Laboratory to Industry
Significant engineering challenges remain before SS-H2 can be widely deployed. Electrolyzers require components in practical forms — metal meshes and foams — not just laboratory samples. However, the team has begun moving toward industrial production.
"From experimental materials to real products, such as meshes and foams, for water electrolyzers, there are still challenging tasks at hand," Professor Huang added. "Currently, we have made a big step toward industrialization. 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."
Implications for Green Hydrogen
Green hydrogen — produced by splitting water using renewable electricity — is widely seen as a critical energy carrier for decarbonizing sectors that are difficult to electrify directly, including steelmaking, shipping, and long-duration energy storage. However, the cost of electrolysis equipment remains a major barrier to widespread adoption.
Seawater electrolysis is particularly attractive because it avoids the need for desalination infrastructure, but the corrosive chloride environment has limited material options to expensive titanium-based alloys. If SS-H2 performs reliably in commercial electrolyzers, it could substantially reduce the capital cost of seawater-based hydrogen production systems.
Sources
- University of Hong Kong press release, 11 August 2026
- ScienceDaily, "'Cannot be explained' — New super steel stuns scientists," 11 August 2026
- Yu, K., Feng, S., Ding, C., Gu, M., Yu, P., Huang, M. "A sequential dual-passivation strategy for designing stainless steel used above water oxidation." Materials Today, 2023; 70: 8. DOI: 10.1016/j.mattod.2023.07.022
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