Seawater purification technique outperforms commonly used materials, even activated carbon

Researchers have discovered a new technique for improving the electrodes that convert seawater into potable water using oxygen. The findings were reported in Nature Communications. The research was led by Yusuke Yamauchi at Nagoya University, Japan in collaboration with Xingtao Xu at Zhejiang Ocean University,

“As the world’s population has been increasing, water scarcity will likely become a critical issue,” Yamauchi said, explaining the motivation behind the study. “We were excited to develop a material that outperformed all existing materials, even activated carbon.”

The technique works by removing ions from seawater using electrodes, leaving deionized, drinkable water. In the process, ions from seawater are attracted to the electrode surface and charged ions are stored in an electric double layer formed there. In addition to purifying water, the ions can be extracted from the electrodes following separation, allowing useful ions, such as sodium, to be repurposed for industrial processes.

The most commonly used electrodes are porous carbonaceous electrodes, which use a carbon and nitrogen base with pores to create a high surface area for extracting ions from liquids. The researchers theorized that ‘heteroatom doping,’ which introduces atoms to alter a material’s structure and improve performance, could improve electrode conductivity and stability.

“We used oxygen for doping, as oxygen creates synergistic effects with nitrogen that increase the adsorption of ions. We found that in the presence of oxygen, the affinity of nitrogen for ions was increased,” Asakura said. “We were excited to discover that oxygen affects capacitive deionization. Our team was the first to demonstrate this role of it.”

An unexpected benefit emerged when the researchers discovered that oxygen-doped electrodes had even greater surface area, likely because the doping process changed the carbonization activity. This increased surface area enhances the purification efficiency.

Yamauchi believes their findings are an important reminder for researchers not to neglect certain techniques. “Other groups overlooked the potential use of oxygen in this process,” he said. “That’s why we included ‘unveiling the neglected role of oxygen doping’ in the paper’s title.”

Although carbon-based materials are already relatively inexpensive, the researchers believe that their findings will further reduce the cost of purifying water, making the technology more accessible to underserved coastal communities facing freshwater shortages. Beyond water purification, this innovation has promising applications in the automotive industry, where similar electrodes are vital components in fuel cells, particularly those used in hydrogen-powered vehicles.