“Cannot be explained” – New ultra stainless steel stuns researchers
Science News
from research organizations
“Cannot be explained” – New ultra stainless steel stuns researchers
Date:
May 10, 2026
Source:
The University of Hong Kong
Summary:
A team at the University of Hong Kong has developed a new “super steel” that can survive the harsh conditions needed to make green hydrogen from seawater. The material uses an unexpected double-protection mechanism that resists corrosion far better than conventional stainless steel. Even more impressive, it could replace costly titanium parts used in today’s hydrogen systems.
Share:
FULL STORY
The novel stainless steel for hydrogen developed by the team. Credit: The University of Hong Kong
A stainless steel breakthrough from the University of Hong Kong (HKU) could help solve one of the biggest problems facing green hydrogen: how to build electrolyzers that are tough enough for seawater, yet cheap enough for large scale clean energy.
Led by Professor Mingxin Huang in HKU's Department of Mechanical Engineering, the team developed a special stainless steel for hydrogen production (SS-H2). The material resists corrosion under conditions that normally push stainless steel past its limits, making it a promising candidate for producing hydrogen from seawater and other harsh electrolyzer environments.
The discovery, reported in Materials Today in the study "A sequential dual-passivation strategy for designing stainless steel used above water oxidation," builds on Huang's long running "Super Steel" Project. The same research program previously produced anti-COVID-19 stainless steel in 2021, along with ultra strong and ultra tough Super Steel in 2017 and 2020.
A Cheaper Path Toward Green Hydrogen
Green hydrogen is made by using electricity, ideally from renewable sources, to split water into hydrogen and oxygen. Seawater is an especially tempting feedstock because it is abundant, but it brings a serious materials problem: salt, chloride ions, side reactions, and corrosion can quickly damage electrolyzer components.
Recent reviews of direct seawater electrolysis continue to highlight the same core challenge. The technology could provide a more sustainable route to hydrogen, but corrosion, chlorine related side reactions, catalyst degradation, precipitates, and limited long term durability remain major obstacles to commercial use.
That is where SS-H2 could matter. In a salt water electrolyzer, the HKU team found that the new steel can perform comparably to the titanium based structural materials used in current industrial practice for hydrogen production from desalted seawater or acid. The difference is cost. Titanium parts coated with precious metals such as gold or platinum are expensive, while stainless steel is far more economical.
For a 10 megawatt PEM electrolysis tank system, the total cost at the time of the HKU report was estimated at about HK$17.8 million, with structural components making up as much as 53% of that expense. According to the team's estimate, replacing those costly structural materials with SS-H2 could reduce the cost of structural material by about 40 times.
Why Ordinary Stainless Steel Fails
Stainless steel has been used for more than a century in corrosive environments because it protects itself. The key ingredient is chromium. When chromium (Cr) oxidizes, it creates a thin passive film that shields the steel from damage.
But that familiar protection system has a built in ceiling. In conventional stainless steel, the chromium based protective layer can break down at high electrical potentials. Stable Cr2O3 can be further oxidized into soluble Cr(VI) species, causing transpassive corrosion at around ~1000 mV (saturated calomel electrode, SCE). That is well below the ~1600 mV needed for water oxidation.
Even 254SMO super stainless steel, a benchmark chromium based alloy known for strong pitting resistance in seawater, runs into this high voltage limit. It may perform well in ordinary marine settings, but the extreme electrochemical environment of hydrogen production is a different challenge.
The Steel That Builds a Second Shield
The HKU team's answer was a strategy called "sequential dual-passivation." Instead of relying only on the usual chromium oxide barrier, SS-H2 forms a second protective layer.
The first layer is the familiar Cr2O3 based passive film. Then, at around ~720 mV, a manganese based layer forms on top of the chromium based layer. This second shield helps protect the steel in chloride containing environments up to an ultra high potential of 1700 mV.
That is what makes the finding so striking. Manganese is usually not viewed as a friend of stainless steel corrosion resistance. In fact, the prevailing view has been that manganese weakens it.
"Initially, we did not believe it because the prevailing view is that Mn impairs the corrosion resistance of stainless steel. Mn-based passivation is a counter-intuitive discovery, which cannot be e