A team at the University of Hong Kong (HKU) has developed a new stainless steel that overcomes a fundamental weakness of conventional stainless steel — and could dramatically lower the cost of producing green hydrogen.
The material, named SS-H2 (stainless steel for hydrogen) and led by Professor Mingxin Huang of HKU's Department of Mechanical Engineering, resists severe corrosion under conditions that ordinary stainless steel cannot withstand. In a saltwater electrolyzer, the new steel delivered performance comparable to titanium structural components used to produce hydrogen — at a fraction of the cost. The researchers estimate the material could cut the cost of structural materials by roughly 40 times. The findings were published in Materials Today, with patents filed in several countries and two already authorized.
Why it matters: green hydrogen is made by electrolysis, which uses electricity to split water into hydrogen and oxygen. The equipment must endure demanding chemical and electrical conditions — especially with salt involved. Titanium, the material of choice for many components, is expensive to extract, refine and machine.
Conventional stainless steel hits a hard limit: the protective chromium oxide layer (Cr2O3) can be further oxidized at about 1000 mV, entering a degradation known as transpassive corrosion. But water oxidation — the essential reaction of electrolysis — requires a substantially higher potential of about 1600 mV. Huang's group found a way around that limit using what they call "sequential dual-passivation": SS-H2 develops a second, manganese-based protective layer on top of the chromium oxide, starting at about 720 mV. Together, the two layers resist corrosion in chloride environments at potentials reaching 1700 mV.
Especially striking is the role of manganese — an element long regarded as harmful to the corrosion resistance of stainless steel. "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 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," said Dr. Kaiping Yu, the study's first author.
The project took nearly six years. Now the material is moving toward industry: tons of SS-H2-based wire have already been produced with a factory on the mainland. "From experimental materials to real products, such as meshes and foams, for water electrolyzers, there are still challenging tasks at hand. Currently, we have made a big step toward industrialization," Huang said. A 10-megawatt PEM electrolysis system currently costs about HK$17.8 million, with structural components representing as much as 53% of the total — exactly where SS-H2 could offer the biggest lever.
