Scientists Discover a Cheaper, More Powerful Catalyst for Clean Hydrogen Energy

Scientists used a nanoparticle megalibrary to uncover a low-cost, high-performing alternative to iridium, unlocking a faster path to affordable hydrogen energy.

The Search for Iridium Alternatives

For years, scientists across the globe have been working to replace iridium, a precious and extremely costly metal that plays a key role in producing clean hydrogen fuel.

Recently, researchers succeeded in identifying a substitute using a groundbreaking tool, and they did it in just one afternoon.

Developed at Northwestern University, the tool is known as a megalibrary. Described as the world’s first nanomaterial “data factory,” a single megalibrary holds millions of carefully designed nanoparticles arranged on a chip no larger than a fingertip.

Working together with the Toyota Research Institute (TRI), the Northwestern team used this platform to pinpoint promising catalysts for hydrogen generation. After identifying a candidate, they then scaled it up and proved that the material could perform inside an actual device, all in remarkably short time.

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A Megalibrary for Materials Discovery

The megalibrary allowed scientists to test countless combinations of four metals that are abundant, inexpensive, and already known for their catalytic properties. From this massive screening effort, the researchers uncovered an entirely new material. In laboratory trials, it not only matched but, in some cases, outperformed commercial iridium-based catalysts, while costing only a fraction of the price.

The implications reach far beyond lowering the price of green hydrogen. The success also highlights the potential of the megalibrary approach itself, which could revolutionize how new materials are discovered across a wide range of fields.

The study was published on August 19 in the Journal of the American Chemical Society (JACS).

A New Way to Find the Best Materials

“We’ve unleashed arguably the world’s most powerful synthesis tool, which allows one to search the enormous number of combinations available to chemists and materials scientists to find materials that matter,” said Chad A. Mirkin, George B. Rathmann Professor of Chemistry at Northwestern University, senior author and primary inventor of the megalibrary platform. “In this particular project, we have channeled that capability toward a major problem facing the energy sector. That is: How do we find a material that is as good as iridium but is more plentiful, more available and a lot cheaper? This new tool enabled us to find a promising alternative and to find it rapidly.”

A nanotechnology pioneer, Mirkin is also a professor of chemical and biological engineering, biomedical engineering and materials science and engineering at the McCormick School of Engineering, and executive director of the International Institute for Nanotechnology. He co-led the work with Ted Sargent, Lynn Hopton Davis and Greg Davis Professor of Chemistry at Northwestern University, professor of electrical and computer engineering at McCormick, and executive director of the Paula M. Trienens Institute for Sustainability and Energy.

Hydrogen’s Iridium Problem

As the world moves away from fossil fuels and toward decarbonization, affordable green hydrogen has emerged as a critical piece of the puzzle. To produce clean hydrogen energy, scientists have turned to water splitting, a process that uses electricity to split water molecules into their two constituent components — hydrogen and oxygen.

The oxygen part of this reaction, called the oxygen evolution reaction (OER), however, is difficult and inefficient. OER is most effective when scientists use iridium-based catalysts, which have significant disadvantages. Iridium is rare, expensive and often obtained as a byproduct from platinum mining. More valuable than gold, iridium costs nearly $5,000 per ounce.

“There’s not enough iridium in the world to meet all of our projected needs,” Sargent said. “As we think about splitting water to generate alternative forms of energy, there’s not enough iridium from a purely supply standpoint.”

A Nanoparticle Army on a Chip

Mirkin, who introduced the megalibraries in 2016, decided with Sargent that finding new candidates to replace iridium was a perfect application for his revolutionary tool. While materials discovery is traditionally a slow and daunting task filled with trial and error, megalibraries enable scientists to pinpoint optimal compositions at breakneck speeds.

Each megalibrary is created with arrays of hundreds of thousands of tiny, pyramid-shaped tips to print individual “dots” onto a surface. Each dot contains an intentionally designed mix of metal salts. When heated, the metal salts are reduced to form single nanoparticles, each with a precise composition and size.

“You can think of each tip as a tiny person in a tiny lab,” Mirkin said. “Instead of having one tiny person make one structure at a time, you have millions of people. So, you basically have a full army of researchers deployed on a chip.”

The Winning Catalyst Emerges

In the new study, the chip contained 156 million particles, each made from different combinations of ruthenium, cobalt, manganese and chromium. A robotic scanner then assessed how well the most promising particles could perform an OER. Based on these tests, Mirkin and his team selected the best-performing candidates to undergo further testing in the laboratory.

Eventually, one composition stood out: a precise combination of all four metals (Ru52Co33Mn9Cr6 oxide). Multi-metal catalysts are known to elicit synergistic effects that can make them more active than single-metal catalysts.

“Our catalyst actually has a little higher activity than iridium and excellent stability,” Mirkin said. “That’s rare because oftentimes ruthenium is less stable. But the other elements in the composition stabilize ruthenium.”

Proving Stability and Cost Benefits

The ability to screen particles for their ultimate performance is a major new innovation. “For the first time, we were not only able to rapidly screen catalysts, but we saw the best ones performing well in a scaled-up setting,” said Joseph Montoya, Senior Staff Research Scientist at TRI and study co-author.

In long-term tests, the new catalyst operated for more than 1,000 hours with high efficiency and excellent stability in a harsh acidic environment. It is also dramatically cheaper than iridium — about one-sixteenth of the cost.

“There’s lots of work to do to make this commercially viable, but it’s very exciting that we can identify promising catalysts so quickly — not only at the lab scale but for devices,” Montoya said.

Beyond Hydrogen: The Bigger Picture

By generating massive high-quality materials datasets, the megalibrary approach also lays the groundwork for using artificial intelligence (AI) and machine learning to design the next generation of new materials. Northwestern, TRI and Mattiq, a Northwestern spinout company, have already developed machine learning algorithms to sift through the megalibraries at record speeds.

Mirkin says this is only the beginning. With AI, the approach could scale beyond catalysts to revolutionize materials discovery for virtually any technology, such as batteries, biomedical devices and advanced optical components.

“We’re going to look for all sorts of materials for batteries, fusion and more,” he said. “The world does not use the best materials for its needs. People found the best materials at a certain point in time, given the tools available to them. The problem is that we now have a huge infrastructure built around those materials, and we’re stuck with them. We want to turn that upside down. It’s time to truly find the best materials for every need — without compromise.”

Reference: “Accelerating the Pace of Oxygen Evolution Reaction Catalyst Discovery through Megalibraries” by Jin Huang, Zhe Wang, Jiashun Liang, Xiao-Yan Li, Jacob Pietr