Stainless steel has long been a fundamental material used in corrosive environments due to its high corrosion resistance. However, the conventional single-passivation mechanism based on chromium (Cr) has limited the further advancement of stainless steel. The oxidation of stable Cr2O3 into soluble Cr(VI) species causes transpassive corrosion, which hinders stainless steel’s potential for water oxidation. However, a research team led by Professor Mingxin Huang at the Department of Mechanical Engineering of the University of Hong Kong (HKU) has recently achieved a significant breakthrough in stainless steel for hydrogen production from seawater. This “Super Steel” project has developed stainless steel for hydrogen (SS-H2) that exhibits high corrosion resistance, surpassing conventional stainless steel.
By utilizing a “sequential dual-passivation” process, Professor Huang’s team successfully created SS-H2 with superior corrosion resistance. Unlike traditional stainless steel, the SS-H2 forms a secondary manganese (Mn)-based layer on top of the chromium-based layer. This dual-passivation mechanism prevents corrosion in chloride media, providing SS-H2 with an ultra-high potential of 1700 mV, far surpassing conventional stainless steel. The introduction of the Mn-based layer is a counter-intuitive discovery as it contradicts current knowledge in corrosion science. Nonetheless, numerous atomic-level results convinced the researchers of the effectiveness of this innovative approach.
Professor Huang’s team focused on developing high-potential-resistant alloys, unlike traditional corrosion studies that concentrate on resistance at natural potentials. This breakthrough in stainless steel for hydrogen production opens up new possibilities for industrial applications. Currently, expensive materials like gold (Au)- or platinum (Pt)-coated titanium (Ti) are required for structural components in water electrolyzers. These materials contribute significantly to the overall expense of such systems. However, with the development of SS-H2, these costly structural components can be replaced by more economical stainless steel. The expected cost reduction of structural materials by about 40 times makes SS-H2 a highly promising alternative for industrial applications.
The breakthrough made by Professor Huang’s team marks a crucial step towards industrialization. Collaborating with a factory from the Mainland, the team has already produced tons of SS-H2-based wire. This progress paves the way for the application of SS-H2 in hydrogen production from renewable sources. While challenges remain in transforming SS-H2 from experimental materials to real products, such as meshes and foams, for water electrolyzers, the research team is optimistic about the future. The cost-effective and high corrosion-resistant nature of SS-H2 offers extensive possibilities for green hydrogen production, especially from seawater, where sustainable solutions are still in development.
The groundbreaking research led by Professor Mingxin Huang and his team at the University of Hong Kong has revolutionized the field of stainless steel for hydrogen production. By utilizing a sequential dual-passivation process, they successfully developed SS-H2 with superior corrosion resistance and high potential for industrial applications. This breakthrough not only challenges conventional knowledge but also provides cost-effective alternatives to expensive materials currently employed in water electrolyzers. As the world continues to pursue sustainable energy solutions, SS-H2 offers a promising avenue for producing green hydrogen from renewable sources. With ongoing efforts towards industrialization, the future of stainless steel for hydrogen production looks brighter than ever before.