The decades-long search for an alternative to iridium, one of the rarest and most expensive metals on Earth, may finally be over, with a new discovery that could accelerate the push for affordable clean hydrogen technologies.
Remarkably, researchers at Northwestern University behind the discovery say they found a viable substitute in just a single afternoon.
By leveraging a powerful new nanomaterial data factory that researchers call a “megalibrary,” the team was able to screen millions of nanoparticles on a single chip at record speeds. Through a collaboration with the Toyota Research Institute (TRI), the team’s powerful new tool helped them uncover a new catalyst made from abundant metals that performs in ways on par with, or even better than, commercial iridium-based materials.
The discovery could help facilitate less expensive green hydrogen production and highlights the promise of the megascale library approach in significantly advancing materials discoveries across various industries.
Reinventing Materials Discovery
In the past, identifying new materials has often been a painstaking process of trial and error.
To combat this, nanotechnology pioneer Chad Mirkin created megalibraries—a novel platform where each individual chip contains up to millions of nanoparticles printed with arrays of pyramid-shaped structures that deposit precise mixes of metallic salts.
Mirkin, the senior author of a new study published in the Journal of the American Chemical Society, which describes the team’s findings, said that each pyramid-shaped tip can be thought of as a tiny lab unto itself. When heated, the mixtures they deposit form nanoparticles with tightly controlled compositions and sizes.
“Instead of having one tiny person make one structure at a time, you have millions,” Mirkin explained in a statement. “So, you basically have a full army of researchers deployed on a chip.”
Searching for an Iridium Alternative
Armed with this innovative technology, the team decided to apply it toward a major hurdle in the production of green hydrogen energy: the oxygen evolution reactor (OER), which involves a step in water splitting that currently relies on iridium as a catalyst.
One of the major issues with the use of iridium is its cost. Currently, this rare Earth metal is valued at close to $5,000 per ounce and is mined only as a byproduct of another rare Earth metal: platinum. This makes it both too rare and too costly to support global clean energy demands.
“There’s not enough iridium in the world to meet all of our projected needs,” said Ted Sargent, a Northwestern researcher and co-author of the recent paper.
However, with help from Mirkin’s megalibrary, the Northwestern team was able to screen combinations of four metals—ruthenium, cobalt, manganese, and chromium—with remarkable speed. The chip used as the sample for this screening contained 156 million nanoparticles, and a robotic scanner evaluated their performance in terms of OER.
A Winning Catalyst
Following the team’s analysis, a clear winner stood out among the compositions they examined: a multi-metal oxide with the formal designation of Ru52Co33Mn9Cr6. This specific blend not only appeared to be an almost perfect match for iridium’s activity, but remarkably, it appeared to exceed it in at least a few tests.
Additionally, the novel multi-metal oxide showed promising indications of offering long-term stability that also exceeded that of iridium.
“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 it.”
Furthermore, durability tests demonstrated that the new catalyst could operate for over 1,000 hours under extremely harsh, acidic conditions without experiencing significant efficiency loss. Best of all, it’s production cost clocks in at close to one-sixteenth that of iridium, making it a far more commercially viable alternative.
Although additional research is still required, the team says the results are extremely promising.
“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,” said TRI’s Joseph Montoya, a co-author of the study.
Advancing Beyond Hydrogen
Even beyond the team’s most recent achievement, their study demonstrates how megalibraries can be leveraged to assemble massive datasets that can be paired with artificial intelligence and machine learning to provide new avenues for discovery in materials science.
Mirkin believes what his team has achieved is really is just the beginning of more exciting discoveries to come.
“The world does not use the best materials for its needs,” he said. “People found the best materials at a certain point in time, given the tools available to them.”
“We want to turn that upside down,” Mirkin added. “It’s time to truly find the best materials for every need — without compromise.”
The team’s discovery was detailed in the recent paper, “Accelerating the Pace of Oxygen Evolution Reaction Catalyst Discovery through Megalibraries,” published in the Journal of the American Chemical Society.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.