Researchers at Brookhaven National Laboratory, the University of Pittsburgh, and Drexel University in Philadelphia are looking for a more sustainable way to disinfect water. They are studying how electrochemical ozone production (EOP) works at the molecular level to develop a better catalyst that is efficient, economical, and long-lasting. The study was published in the ACS Catalysis journal.
A representation of electrical ozone production and the investigation of what happens at the molecular level. Image Credit: John Keith
In the future, centralized chlorine treatments currently employed in urban centers or rural communities may give way to scalable electrochemical ozone production (EOP) technologies for disinfecting contaminated water. Yet, our understanding of EOP at the molecular level and the development of efficient, affordable, and sustainable enabling technologies remain lacking.
The lead author, Drexel Ph.D. student Rayan Alaufey, collaborated with researchers from Drexel University, including co-PI Maureen Tang, associate professor of chemical and biological engineering, postdoctoral researcher Andrew Lindsay, Ph.D. student Tana Siboonruang, and Ezra Wood, associate professor of chemistry. Co-PI John A. Keith, associate professor of chemical and petroleum engineering, along with graduate student Lingyan Zhao from the University of Pittsburgh, and Qin Wu from Brookhaven National Laboratory, also contributed to the study.
People have used chlorine to treat drinking water since the 19th century, but today we better understand that chlorine may not always be the best option. EOP for example can generate ozone, a molecule with about the same disinfecting power as chlorine, directly in water. Unlike chlorine which stably persists in water, ozone in water naturally decomposes after about 20 minutes, meaning it is less likely to damage people when consumed from water at a tap, when swimming in a pool, or when cleaning wounds in a hospital.
John A. Keith, Associate Professor of Chemical and Petroleum Engineering, University of Pittsburgh
Keith, who is also the R.K. Mellon Faculty Fellow in Energy at Pitt's Swanson School of Engineering, said, “EOP for sustainable disinfection would make a lot of sense in some markets, but doing it requires a good enough catalyst, and because nobody has found a good enough EOP catalyst yet, EOP is too expensive and energy-intensive for broader use. My colleagues and I thought if we could decode at the atomic level what makes a mediocre EOP catalyst work, maybe we could engineer an even better EOP catalyst.”
Understanding the mechanism of action of nickel- and antimony-doped tin oxide (Ni/Sb–SnO2, or NATO), one of the most promising and least toxic EOP catalysts to date, will help engineers in better designing this material.
According to Keith, the problem lies in deciphering NATO's role at the atomic level in facilitating EOP. Does ozone form because the catalyst is breaking down, necessitating further efforts to enhance the stability of NATO catalysts, or is ozone forming catalytically in ways desired by researchers?
Surprisingly, the researchers discovered that it is probably a mix of both.
Through experimental electrochemical analyses, mass spectrometry, and computational quantum chemistry modeling, the researchers constructed an "atomic-scale storyline" elucidating how ozone is generated on NATO electrocatalysts. For the first time, they identified that some of the nickel in NATO likely leaches out of the electrodes via corrosion. These nickel atoms, now dispersed in the solution near the catalyst, can catalyze chemical reactions that ultimately lead to ozone generation.
If we want to make a better electrocatalyst, we need to understand what parts are working and not working. Factors like metal ion leaching, corrosion, and solution phase reactions can give the appearance that a catalyst is working one way when it is working another way.
John A. Keith, Associate Professor of Chemical and Petroleum Engineering, University of Pittsburgh
Keith pointed out that before other researchers can work toward improving EOP and other electrocatalytic processes, it is crucial to determine the frequency of corrosion and chemical reactions that take place away from the catalyst.
In conclusion, the scientists note that “Identifying or refuting the existence of such fundamental technological constraints will be critical to any future applications of EOP and other advanced electrochemical oxidation processes.”
“We know that electrochemical water treatment works on small scales, but the discovery of better catalysts will boost it to a global scale. The next step is finding new atomic combinations in materials that are more resistant to corrosion but also promote economically and sustainably viable EOP,” Keith said.
Journal Reference:
Alaufey, R., et al. (2024) Interplay between Catalyst Corrosion and Homogeneous Reactive Oxygen Species in Electrochemical Ozone Production. American Chemical Society Catalysis. doi.org/10.1021/acscatal.4c01317.