Iridium oxide is one of the most important — and most problematic — materials in the global push toward clean energy. It is currently the most reliable catalyst used in the conversion of energy to chemicals by electrolysis, a process that uses electricity to split water molecules into oxygen and hydrogen.
But iridium is among the rarest non-radioactive elements in Earth’s crust, and not unlike metal rusting over time, iridium oxide catalysts slowly degrade under the harsh acidic and high-voltage conditions required for electrolyzers (the devices used for electrolysis) to operate.
A new federally funded study by researchers at Duke University and the University of Pennsylvania offers an unprecedented view of that degradation process, capturing how iridium oxide nanocrystals restructure and dissolve — atom by atom — during electrolysis. The findings provide critical insight into why today’s best catalysts still fail and how future materials might last longer.
“When we pair them with solar or wind energy, we have the potential to completely get rid of fossil fuels using these methods, but there is not enough iridium on Earth to meet today’s current level of energy use,” said Ivan A. Moreno-Hernandez , assistant professor of Chemistry at Duke and senior author of the paper. “We really want to design materials that use iridium more effectively, or, eventually, get rid of iridium completely.”
Much of what scientists know about catalyst degradation comes from indirect measurements, tracking how much metal is lost over time or comparing “before” and “after” images of particles. In this study, the researchers took a different approach: they watched the process unfold in real time.
Using advanced electron microscopy, computer simulations and device-scale testing, the researchers followed how crystal surfaces changed shape, atom by atom, as dissolution progressed.
What they saw challenges the idea that catalyst degradation is a simple, uniform process.
“The ability to watch these materials fall apart at the scale of atoms and in real time is an extremely exciting development,” said S. Avery Vigil , graduate student at Duke and first-author of the article. “We are learning so much about how catalysts behave during operation.”
Rather than dissolving evenly, iridium oxide nanocrystals underwent pronounced surface shape changes. Surfaces that were initially flat and relatively stable atomic planes, like a smooth sheet of ice, gradually transformed into stepped, irregular and defect-prone surfaces.
More strikingly, different facets of the same particle could undergo different dissolution mechanisms at the same time — like an ice block being picked on one side and melted on the other. These distinct mechanisms included gradually losing atoms, surface roughening through reconstruction of entire atomic layers and entire layers of atoms peeling away from the surface in a process called delamination.
“The results were incredible,” said Moreno-Hernandez. “Everybody, myself included, assumed that degradation happened one atom at a time, but we are seeing thousands of atoms being removed at once in this collective behavior. It's kind of like a block tower game, you remove one little piece, and it all falls apart. It was very unexpected.”
To understand why some surfaces dissolved more readily than others, the team turned to pen, paper and mathematics — or rather incredibly computationally intensive theoretical modeling. Over more than 50,000 hours of computer time, the researchers modeled how iridium oxide particles are expected to naturally reorganize themselves under the high voltages used in water splitting. Their results indicate that, under the operating conditions, the most energetically stable surfaces are the ones with more steps and kinks — exactly the kinds of facets that emerged during the microscopy experiments.
Using a different type of simulation, they revealed that iridium atoms are more easily removed from certain facets of iridium oxide nanocrystals than others. This facet-dependent behavior helps explain why dissolution often initiates and accelerates at specific regions of the particle.
“Because we were able to scale down the experiment to see the atomic structure, we're also able to scale up the theory to look at this collective behavior, and we're getting a lot closer to being able to have an apples-to-apples comparison between theory and experiment,” said Moreno-Hernandez. “That’s very exciting as scientists.”
Finally, to confirm that these nanoscale observations were relevant to real devices, the team examined iridium oxide catalysts recovered from a water electrolyzer operated for 100 hours at industrially relevant current densities.
The post-mortem catalyst analysis revealed the same trend seen in the microscope: an increase in rugged high-index facets and a corresponding reduction in smooth, low-index surfaces. These morphological changes occurred alongside an increase in the voltage required to maintain the same current, linking atomic-scale restructuring to measurable performance degradation.
“Now that we understand how iridium oxide surfaces restructure and dissolve as they degrade, we can develop methods that allow us to minimize these collective dissolution mechanisms, and ultimately design more durable catalysts,” said Moreno-Hernandez, whose research is funded in part through an NSF CAREER Award.
The impacts of this study are far broader, though. “The exciting thing about this study isn’t one thing,” he said, “it’s the convergence of everything. It’s the advancement in microscopy, in computational resources, in the array of tools we used to build this framework.
“If you had told me when I was a kid that one day we would be able to film atoms, I would have thought that it was science fiction. Now it's a reality.”
Journal of the American Chemical Society
Observational study
Not applicable
Direct observation of collective dissolution mechanisms in iridium oxide nanocrystals
4-Feb-2026