Water molecule structures regulate chloride ion diffusion

December 8, 2025

Toward practical use of low-grade water for electrolysis

Researchers from RIKEN CSRS have demonstrated that hydration structures formed by ions in aqueous solutions regulate the diffusion of chloride ion impurities and enhance the efficiency of water electrolysis.
Water electrolysis is attracting interest as a technique to produce hydrogen and chemical fuels using renewable energy. However, even trace amounts of chloride ions in the electrolyte can be oxidized into toxic and corrosive chlorine gas instead of water. Therefore, highly pure water is currently used for electrolysis. To realize widespread water electrolysis amid a global shortage of fresh water, chloride-tolerant electrolysis technology is necessary.
In this study, the research group found that chloride ion diffusion is highly affected by coexisting cations in the electrolyte. They demonstrated that the hydration structures become more rigid and can suppress chloride ion diffusion more effectively in the order of Li⁺ > Na⁺ > H⁺ > K⁺ > Cs⁺, leading to a reduction in chlorine gas evolution by up to 33%. While the effects of catalytic activity and coexisting ions have been previously reported, this is the first study to report that the hydration structures composed of ions and water molecules regulate mass transport. 

As diffusion is independent of the catalyst material, these findings are expected to contribute to diversifying water sources usable for water electrolysis.

 

Original article

Nature Chemistry　doi: 10.1038/s41557-025-02014-4

T. Lim, H. Ooka, Y. Yu, T. Murakami, S. Wada, R. Nakamura,

"Hydration entropy of cations regulates chloride ion diffusion during electrochemical chlorine evolution".

Contact

Ryuhei Nakamura; Team Director
Taejung Lim; Special Postdoctoral Researcher
Hideshi Ooka; Research Scientist
Biofunctional Catalyst Research Team