New Study Changes Understanding of Green Hydrogen Catalyst Lifespan

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NORMAN, OKLA. – A new study published in Nature Catalysis is upending long-held beliefs about the lifespan of iridium oxide, the state-of-the-art catalyst material used to generate green hydrogen, which plays a key role in efforts to decarbonize industries and advance clean energy. University of Oklahoma Professor Kasun Gunasooriya, Ph.D. is part of the research team to make this breakthrough.

The novelty of the research findings lies in the discovery of changes in the structure of iridium oxide as it is used. The scientists found that iridium does not become fully amorphous after prolonged use but develops short-range order patterns.

“We always assume a catalyst is a stiff structure that doesn’t change significantly under reaction conditions. But in reality, when you operate these devices long term, the materials undergo drastic changes and during water electrolysis, materials dissolve in the acidic environment and the high applied potential,” Gunasooriya said.

He compares a catalyst to a phone battery: at purchase, a phone battery operates at 100% efficiency, but in five years, that battery’s capacity has decreased to perhaps 75% or lower.  

“What we found when we tried to model some of these short-range catalyst surface patterns was that those newly generated surface iridium atoms are more active than the original iridium,” he added.

The discovery could mean big savings for green hydrogen. Though hydrogen itself is colorless, different colors are used to categorize the significance of emissions releases during different methods of hydrogen production. According to the Society of Petroleum Engineers, black hydrogen comes from coal gasification, while gray hydrogen comes from fossil fuels. One form of green hydrogen is produced by electrolysis, the process of splitting water molecules into hydrogen and oxygen with green electricity, a method that does not create greenhouse gas emissions.

Gunasooriya says that the process of producing hydrogen through electrolysis is expensive, approximately $5 per kilogram of hydrogen versus the $1 per kilogram when producing black hydrogen. The steep cost comes from the catalyst necessary to create the reaction.

“The best catalyst we have for water electrolysis is iridium oxide,” Gunasooriya said. He describes iridium oxide as stable and other more abundant possible catalysts, such as iron or cobalt, are less stable under acidic water electrolysis. “Those are not good catalysts because what we want is a catalyst that can operate for a long time.”

If iridium is the best catalyst for the job, then reducing the amount of iridium necessary can lower the price of green hydrogen.

The work is in line with the Department of Energy’s Hydrogen Shot, part of the Energy Earthshots Initiative, an effort to advance the clean energy transition. According to the DOE, Hydrogen Shot would reduce the cost of hydrogen from renewable energy costs by 80%.

This research suggests that if scientists can synthesize these specific short-range iridium oxide active sites, then they can actually minimize the amount of iridium put into devices, thereby reducing the price.