University of Pittsburgh researchers have made an important step toward providing hospitals and water treatment facilities with a safer, greener alternative to chlorine-based disinfection.
The team, which includes scientists from Drexel University and Brookhaven National Laboratory, uncovered key design principles for catalysts that can generate ozone, a disinfecting agent, on demand.
This breakthrough addresses a critical challenge in water sanitation. Chlorine, commonly used to kill bacteria on surfaces and in water — including most municipal drinking water — is hazardous to transport and store, and its byproducts can be carcinogenic. These risks limit its use and motivate the search for safer disinfectants.
With the right catalyst, water electrolysis can generate the less hazardous and more sustainable ozone, but limited understanding of how ozone-forming catalysts work has hindered progress. By identifying which surface defects accelerate ozone formation and which trigger corrosion that stops ozone formation, the team has revealed the characteristics necessary for active and stable next-generation catalysts.
"Catalysts can make exciting chemistry possible, but catalysts themselves break down over time," said John Keith , R.K. Mellon Faculty Fellow in Energy at Pitt's Swanson School of Engineering. "Under extreme electrolysis conditions, exciting chemistry can start happening, but catalysts can also start breaking down quicker, too. In the oxide-based catalysts we have studied, what forms ozone is paradoxically also suppressing its formation. Now that we understand that, it becomes a fun puzzle to solve how to design ozone-generating sites that do not also cause corrosion reactions that ruin the catalyst."
The research team, led by Keith and Drexel Associate Professor Maureen Tang, was supported by the National Science Foundation to study fundamental electrochemical mechanisms of multielectron oxidations. They targeted ozone as a replacement for chlorine because it decomposes into oxygen, eliminating long-term residue concerns. Technologies that generate ozone directly in water wherever disinfection is needed could revolutionize water sanitation practices.
Water electrolysis, a high-energy process where electric currents split water into oxygen and hydrogen gases, can produce ozone instead of oxygen when the right catalyst is used. Among the few known examples, nickel- and antimony-doped tin oxide (NATO) catalysts have been considered the safest and most cost-effective option for electrolysis-based ozone generation. However, they have been observed to degrade too quickly for widespread use.
Solving the catalyst puzzle
Computational work by Lingyan Zhao , then a Pitt chemical engineering PhD student using resources at Brookhaven National Lab's Center for Functional Nanomaterials, provided clues to why NATO catalysts break down so rapidly. Quantum chemistry models pinpointed that defect sites on the catalyst surface play two distinct but critical roles: They enhance ozone generation by enabling rapid electron transfer, but also make the catalyst susceptible to corrosion when water attaches to the surface. There it forms proton-rich networks of hydroxides and water, which are known to be reactive and corrosive.
The lead author of the work, Rayan Alaufey, an international PhD student at Drexel, performed a wide series of experiments to test and validate these hypotheses, leading to the final conclusions, which were published in the journal ACS Catalysis .
"This work is a testament to how fundamental science and engineering come together to answer long-standing questions and concoct new routes to improved water sanitation technologies," Keith said.
