A highly active and selective molecular catalyst and electrified membrane

Some chemicals create environmental problems; others, fortunately, can help clean them up. Chemists from Yale University and their colleagues have developed an electrochemical catalyst and membrane that offers an efficient and sustainable way to treat water contaminated with trichloroethylene (TCE), a common and persistent environmental pollutant. Their findings highlight the potential for advanced electrochemical treatments in environmental remediation and open the door for further innovations in the field.

Their results were published in Carbon Future.

TCE is a common industrial solvent or cleaning agent used in refrigerants, dry cleaning, and metal and electronic degreasing. However, TCE’s toxic properties can cause harm to multiple organs and induce cancer. Water contamination by TCE is not uncommon.

While bioremediation was one of the first methods used to tackle TCE pollution, it is often slow and generates byproducts that are even more toxic. Chemical remediation is faster and more efficient but often requires strong chemicals and does not completely decompose TCE. Consequently, electrochemical treatment, which uses electrical currents to decompose contaminants, is emerging as a more effective and sustainable solution for TCE remediation.

“Electrochemical methods have shown promise for treating water contaminated by chlorinated volatile organic compounds, but efficiently removing and repurposing TCE has been a challenge due to the lack of effective catalysts,” said Hailiang Wang, a professor at Yale University’s Department of Chemistry and Energy Sciences Institute and the lead corresponding author of this study.

Responding to this need, the research team developed a catalyst composed of cobalt phthalocyanine (CoPc) molecules mounted on multiwalled carbon nanotubes (CNTs). This catalyst breaks down TCE at record rates, turning it into ethylene and chloride ions with nearly 100% Faradaic efficiency. This means that almost all the electrical current is used to convert TCE into harmless products without generating harmful byproducts, making it promising for practical applications.

“The key to our success is the first electron transfer step, which doesn’t involve protons, and the single site nature of our catalyst,” said Yuanzuo Gao, a graduate student in Wang’s group and the first author of this study. “These helped us avoid the hydrogen evolution reaction and thereby promote TCE dechlorination.”

The hydrogen evolution reaction is a side reaction that consumes electrons that could otherwise be used to break down pollutants, diminishing the current efficiency of the process.

To enhance the practical application of this catalyst, the team incorporated CoPc molecules into an electrified membrane made from reduced graphene oxide (rGO), a modified form of graphene known for its strength, lightweight nature and high conductivity. This membrane filtration device achieved 95% removal of TCE from simulated water samples that mimic actual water treatment conditions, marking a significant advancement in the technology’s practical use.

This study underscores the potential of advanced electrochemical methods to address complex environmental challenges and drive progress in water treatment and industrial pollution control.

“By combining CoPc molecules with CNT and rGO supports, we have created highly selective and active electrocatalysts for the treatment of TCE in water,” Gao said.