When amphiphilic zeolites are used in water, the oxygen reduction reaction goes so well that the platinum catalyst is partly the limiting factor, a US team writes in Nature Catalysis.

If you have a surplus of renewable energy, you can store it as hydrogen and oxygen by electrolysis of water. If you want to get that energy back, you have to do the opposite with the oxygen reduction reaction (ORR). You want to do this as efficiently as possible so that you lose as little energy as possible. A team from Harvard and the Université Grenobles Alpes has found a way to make the ORR almost four times more efficient using dissolved zeolites.

The auxiliary material consists of silicalite-1 nanocrystals, a zeolite consisting of pure silica in a cylindrical crystal structure and containing hydrophobic channels with a hydrophilic exterior (for more on zeolites, see our supporting dossier). The researchers used zeolite because of its high oxygen adsorption capacity: 270 times that of water. As a result, you can get a lot more oxygen into the same amount of water, and the ORR can take place a lot more often. Because of this property, they called the zeolite solution ‘microporous water’. At a concentration of just 6.7% by volume, it provides a current density of 17.5 mA/cm2, 3.9 times higher than without zeolite. Such a high current density also partially limits the activity of the platinum/carbon catalyst, making it much easier to study the catalytic properties.

According to the researchers, this work “illuminates an unexplored area in electrocatalysis, focusing on the use of microporous water to achieve highly concentrated solutions of gases at the electrode, where catalysis can take place at higher current densities due to reduced mass transport constraints.

Thorarinsdottir, A.E. et al. (2023) Nat. Catal., DOI: 10.1038/s41929-023-00958-9