The global transition towards clean energy sources and the decarbonization of the economy faces a key obstacle: the price and availability of materials needed for green hydrogen production. For years, scientists around the world have been searching for a solution to the problem of iridium, a precious metal more valuable than gold, which is crucial for the efficient production of hydrogen from water. Now, thanks to a revolutionary technology developed at the American Northwestern University in collaboration with the Toyota Research Institute (TRI), it seems a solution has been found, and in record time.

A team of researchers has succeeded in discovering a new material that not only matches the performance of iridium but in some aspects surpasses it, all at a fraction of the cost. This breakthrough not only opens the door to significantly cheaper green hydrogen production but also proves the power of a new approach that could fundamentally change the way we discover new materials for everything, from batteries to advanced medicine.

Iridium: The expensive and rare bottleneck of the green transition

Green hydrogen is considered the holy grail of future energy. It is produced through the process of water electrolysis, where electricity is used to split water molecules into oxygen and hydrogen. While hydrogen is the desired product, the oxygen evolution reaction (OER) is the most technically demanding and slowest part of the process. To speed up this reaction and make it more efficient, catalysts are needed, and this is where iridium comes into play.

Iridium has proven to be the most effective and stable catalyst, especially in the acidic conditions typical of PEM electrolyzers, one of the leading technologies for hydrogen production. However, iridium has two huge drawbacks. First, it is one of the rarest elements in the Earth's crust. It is most often obtained as a byproduct of platinum mining, and its annual production is measured in just a few tons. Second, its rarity also dictates an astronomical price. With a price hovering around $5,000 per ounce, it is significantly more expensive than gold. Experts agree: there is simply not enough iridium in the world to meet the projected needs for mass production of green hydrogen. This is a fundamental obstacle hindering the global expansion of the hydrogen economy.

Megalibrary: A nanomaterial factory on a single chip

Faced with this challenge, a team led by Chad A. Mirkin, a nanotechnology pioneer from Northwestern University, applied his revolutionary invention called the "megalibrary." It is a platform that functions as a kind of "data factory" for nanomaterials. On a single tiny chip, smaller than a postage stamp, are millions, even hundreds of millions, of uniquely designed nanoparticles.

The process of creating a megalibrary is fascinating. Arrays with tens of thousands of microscopic, pyramid-like tips are used, each acting as a miniature "nano-pen." These tips deposit tiny droplets of metal salt solutions onto the chip's surface in precisely defined combinations. Each droplet represents a unique "recipe." After all the droplets are deposited, the chip is heated, which leads to the reduction of the salts and the formation of solid nanoparticles, each with a precisely determined chemical composition and size. As Professor Mirkin colorfully explained, "You can imagine each tip as a tiny person in a tiny lab. Instead of one person making one structure, you have millions of people. Basically, you have a whole army of researchers deployed on a single chip."

A lightning-fast search for the ideal replacement

Traditional material discovery is a slow and painstaking process, filled with countless trials and errors. The megalibrary accelerates this process exponentially. In this particular study, the goal was to find a cheap and abundant alternative to iridium. The scientists focused on combinations of four much more available metals known for their catalytic properties: ruthenium, cobalt, manganese, and chromium.

An incredible 156 million unique nanoparticles were created on the chip, each with a different ratio of these four metals. After synthesis, a high-throughput robotic scanner swept across the scene. This automated system quickly and efficiently tested each of the millions of particles to assess its ability to catalyze the oxygen evolution reaction. Based on these preliminary tests, the team identified the most promising candidates and selected them for further, more detailed laboratory testing.

The winning formula: Stability and efficiency without the high price

After rigorous testing, one composition stood out as the absolute winner. It is a specific combination of all four metals in oxide form: Ru52Co33Mn9Cr6. It is known that multimetallic catalysts often exhibit synergistic effects, where the combination of elements yields better results than each element individually. This was confirmed in this case as well.

The new material showed activity that was equal to, and in some tests even slightly higher than, commercial iridium-based catalysts. But the real victory lies in its stability. Ruthenium, which is a good catalyst on its own, is often unstable in aggressive acidic conditions. However, in this combination, cobalt, manganese, and chromium act as stabilizers, giving the material long-term durability. In long-term tests, the new catalyst operated for more than 1,000 hours with high efficiency and outstanding stability in harsh conditions. When the financial aspect is added to this – the estimated cost of this material is about sixteen times less than iridium – it is clear that this is a discovery with enormous potential.

The future is in the fusion of nanotechnology and artificial intelligence

This success is not only important for the future of green hydrogen but also for the entire field of materials science. The megalibrary-based approach generates vast amounts of high-quality data on the relationship between a material's structure and its properties. Such datasets are an ideal foundation for the application of artificial intelligence (AI) and machine learning.

Northwestern University, TRI, and Mattiq, a spinout company from the university lab, have already developed machine learning algorithms that can analyze data from megalibraries at a speed surpassing human capabilities. AI can recognize subtle patterns and correlations and predict which combinations of elements could yield even better results, thus guiding future research. As Professor Mirkin points out, this is just the beginning. The goal is to apply this platform to the search for better materials in almost all technological sectors: from more efficient batteries and materials for fusion reactors to advanced optical components and biomedical devices. We live in a world that often does not use the best possible materials, but rather those that were available with the tools of the past. This technology offers an opportunity to change that and to find the optimal solution for every application, without compromise.