Redox-active metal-organic frameworks (RAMOFs) are highly porous materials made of metals and organic molecules linked together by coordination bonds, and they contain redox-active sites that can store electrons (protons). RAMOFs are promising candidates as electrode-active materials of rechargeable batteries. However, since the coordination bonds in RAMOFs are often prone to decomposition in water, especially in acidic aqueous solutions, their applications as materials for aqueous devices using acidic aqueous solutions have been regarded as a challenge.

To remedy this, a research team from Tohoku University working in collaboration with Keio University, demonstrated a water-resistant and recyclable RAMOF for the first time.

Schematic of this work. ©Kouki Oka et al.

The team prepared a RAMOF, UiO-66-(OH)₂, which contained p-hydroquinone capable of redox reaction to store electrons (protons), while maintaining structural stability in acidic aqueous solutions. They successfully demonstrated, for the first time, that the UiO-66-(OH)₂ worked with high durability in an aqueous RAMOF-based rechargeable battery using an acidic aqueous electrolyte, by storing electrons (protons) throughout the material. After using it as an electrode-active material, UiO-66-(OH)₂ decomposed under mild conditions and was reused (recycled).

"RAMOFs have so many potential uses, and an electrode-active material of an aqueous rechargeable battery is just one of them," explains Kouki Oka, associate professor at Institute of Multidisciplinary Research for Advanced Materials, Tohoku University.

Charging/discharging test and cycle test of the aqueous RAMOF-based rechargeable battery with an acidic aqueous electrolyte. ©Kouki Oka et al.

The findings highlight two key achievements. First, this is the first demonstration showing that an electrode-active material made of a water-resistant RAMOF can stably store electrons even in acidic aqueous solutions. Second, they were able to recycle the RAMOF after using it as an electrode-active material by decomposing the RAMOF back into its raw components in a carbonate aqueous solution and resynthesizing it again for reuse.

"Going forward, we aim to develop new designs that make RAMOFs even more recyclable and adaptable for real-world use," added Oka.

The research was published online in Nature Communications on December 1, 2025.

Schematic of recycling of a RAMOF under mild conditions. ©Kouki Oka et al.