University of Hong Kong Develops Corrosion-Resistant Super Steel That Could Cut Green Hydrogen Costs 40-Fold
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.
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.
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.
