HONG KONG SAR – Media OutReach – November 17, 2023 – A research project led by Professor Mingxin Huang from the Department of Mechanical Engineering at the University of Hong Kong (HKU) has achieved a completely new advancement over conventional stainless steel and the development of stainless steel for hydrogen (SS-H2).
Professor Mingxin Huang and Dr Kaiping Yu
This is another major achievement of Professor Huang’s team in its “Super Steel” project, following the development of anti-COVID-19 stainless steel in 2021, and the ultra-strong and ultra-strong Super Steel -resistant in 2017 and 2020 respectively.
The new steel developed by the team has high corrosion resistance, enabling its potential application for the production of green hydrogen from seawater, where a new sustainable solution is still in the pipeline.
The performance of the new steel in a saltwater electrolyzer is comparable to current industrial practice using titanium as structural parts to produce hydrogen from desalinated seawater or acid, while the cost of the new steel is much cheaper.
The discovery was published in
Materials today in the article titled “A Sequential Double Passivation Strategy for Designing Stainless Steel Used Over Water Oxidation.” The research results are currently the subject of patent applications in several countries, and two of them have already obtained authorization.
Since its discovery a century ago, stainless steel has been an important material widely used in corrosive environments. Chromium is an essential element in establishing the corrosion resistance of stainless steel. A passive film is generated by the oxidation of chromium (Cr) and protects stainless steel in natural environments. Unfortunately, this conventional Cr-based single passivation mechanism has halted the progress of stainless steel. Due to subsequent oxidation of stable Cr2Oh3 in soluble Cr(VI) species, transpassive corrosion inevitably occurs in conventional stainless steel at ~1000 mV (saturated calomel electrode, SCE), which is below the potential required for water oxidation at ~1600mV.
Super stainless steel 254SMO, for example, is a benchmark among Cr-based anti-corrosion alloys and exhibits superior resistance to pitting in seawater; however, transpassive corrosion limits its application to higher potentials.
Using a “sequential double passivation” strategy, Professor Huang’s research team developed the new SS-H2 with superior corrosion resistance. In addition to the single Cr2Oh3Passive Mn-based layer, a secondary Mn-based layer forms on the previous Cr-based layer at ~720 mV. Sequential double passivation mechanism prevents SS-H2 corrosion in chlorinated environments at an ultra-high potential of 1700 mV. The SS-H2 demonstrates a fundamental advance over conventional stainless steel.
“We initially didn’t believe it because the prevailing view is that Mn impairs the corrosion resistance of stainless steel. Mn-based passivation is a counterintuitive finding, which cannot be explained by current knowledge in corrosion science. However, when many atomic atoms “Beyond the surprise, we look forward to exploiting the mechanism,” said Dr. Kaiping Yu, first author of the paper, whose thesis is supervised by Professor Huang.
From the initial discovery of the innovative stainless steel, to achieving a breakthrough in scientific understanding, to preparing for official publication and, hopefully, its industrial application, the team has spent nearly six years at this job.
“Unlike the current corrosion community, which focuses primarily on resistance to natural potentials, we specialize in the development of high potential resistant alloys. Our strategy overcame the fundamental limitation of conventional stainless steel and established a paradigm for the development of alloys applicable to high potentials. This advancement is exciting and brings new applications,” said Professor Huang.
At present, for water electrolyzers in desalinated seawater or acidic solutions, expensive Ti structural components coated with Au or Pt are required. For example, the total cost of a 10 megawatt PEM electrolysis tank system in its current phase is approximately HK$17.8 million, with structural components contributing up to 53% of the overall expense. . The breakthrough by Professor Huang’s team allows these expensive structural components to be replaced with steel more economically. As estimated, the employment of SS-H2 is expected to reduce the cost of structural materials by approximately 40 times, demonstrating great potential for industrial applications.
“From experimental materials to actual products, such as meshes and foams, for water electrolyzers, there are still difficult tasks to be accomplished. Currently, we have taken a big step towards industrialization. Tons of SS-H2-based yarn were produced in collaboration. with a mainland factory. We are making progress in applying the more economical SS-H2 in the production of hydrogen from renewable sources,” added Professor Huang.
Link to document:
https://www.sciencedirect.com/science/article/abs/pii/S1369702123002390
Please
click here for a short video showing how new stainless steel produces hydrogen in salt water.
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