The element hydrogen is a key component of the envisaged energy transition, with an expected capacity of 175 gigawatts by 2030, according to the Hydrogen Council. It is assumed that around 40 percent of this future capacity will be produced using proton exchange membrane (PEM) water electrolysis, a technology that has so far relied on the extremely rare element iridium. As only around nine tons of iridium can be mined per year and it is used in various industries, supply bottlenecks would be inevitable - unless solutions are implemented that reduce the amount of iridium used in PEM applications.

Progress for sustainable hydrogen production

This solution now appears to have been found: Heraeus Precious Metals and Sibanye-Stillwater say they have developed a groundbreaking technological innovation in electrocatalysts for hydrogen production: A new, stable ruthenium-based catalyst for PEM water electrolysis. According to Heraeus, this breakthrough represents significant progress towards sustainable hydrogen production by significantly reducing material costs and reducing dependence on extremely scarce and expensive iridium.

Iridium consumption reduced by 85 percent

With the currently prevailing solutions, around 400 kilograms of iridium are required to build one gigawatt of capacity. To avoid supply bottlenecks, iridium consumption needs to be reduced to less than 100 kilograms per gigawatt. The catalyst presented by Heraeus and Sibanye-Stillwater is therefore primarily based on ruthenium and can save up to 85 percent of the iridium required compared to a pure iridium oxide catalyst. This could reduce potential supply bottlenecks, as the primary global production of ruthenium is 3.5 times greater than that of iridium, according to Heraeus.

Innovative combination of ruthenium and iridium oxide

Like iridium, ruthenium can catalyze the oxygen evolution reaction (OER), which plays a decisive role in PEM electrolysis. Ruthenium even exhibits superior catalytic activity compared to iridium, but such catalysts have so far lacked the necessary stability under the demanding conditions of a PEM electrolyzer. The Heraeus concept is intended to solve this problem by combining both ruthenium and iridium oxide in an innovative way: This allows the necessary stability to be achieved while at the same time utilizing the increased catalytic activity of ruthenium.

Stable despite significantly increased mass activity

The new ruthenium-iridium oxide material class exhibits an immense increase in activity. The catalyst achieves a mass activity up to 50 times higher than before, but - in contrast to pure ruthenium oxide - remains stable under operating conditions. The stability of the new material class was investigated using AD (accelerated degradation) tests: After 30,000 cycles, the new catalyst showed a significantly lower reduction in activity than ruthenium oxide and comparable stability to iridium oxide. These results were verified by Mattiq, a US start-up. Mattiq combines expertise in the fields of chemistry and materials science and carried out high-throughput screening experiments for the development project.

Conversion also has commercial advantages

By using ruthenium, Heraeus is not only helping to reduce potential supply bottlenecks, but also offers significant commercial advantages. According to Heraeus, the concept enables a reduction in capital costs for materials of around 90 percent, which should help to make hydrogen production more economical and efficient.

Dr. Philipp Walter, EVP New Business Development at Heraeus Precious Metals, emphasizes: "The drastic reduction in capital cost per gigawatt with our new ruthenium-based catalyst not only addresses the supply problem of iridium, but also makes economic sense. Solutions like this drive the much-needed expansion of the hydrogen industry and bring us closer to our global green energy goals." Neal Froneman, CEO of Sibanye-Stillwater, added: "As the world's largest producer of primary iridium, we firmly believe that sustainable demand for these metals, with supply in mind, is beneficial to the industry as a whole. The impressive progress Heraeus has made in the work to date is encouraging and we greatly value our partnership in this endeavor."

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