Enhanced activity for the oxygen reduction reaction in microporous water

Abstract

Electrocatalysis of small gas molecules driven by renewable energy sources offers a promising route to carbon-neutral fuels and chemicals. Such small-molecule conversion reactions rely on water as a source of protons and electrons, however, thus limiting energy and power densities owing to the low solubility of gas molecules in water. The oxygen reduction reaction (ORR) is an exemplar of such limitations. Here we demonstrate that the high O2-carrying capacity of aqueous solutions endowed with porosity arising from microporous nanocrystals with hydrophobic internal surfaces and hydrophilic external surfaces—termed microporous water—enhances ORR electrocatalysis in water. Use of silicalite-1 nanocrystals to form an O2-concentrating microporous electrolyte solution increases the ORR current so much that the activity of Pt, typically thought to be an ideal ORR catalyst, is partially limiting, thus allowing the intrinsic catalytic ORR activity of Pt to be measured directly. Electrocatalytic processes involving gas molecules are generally limited by low solubility in aqueous solutions. Here water endowed with permanent microporosity by silicalite-1 nanocrystals is used to concentrate O2, allowing the measurement of the intrinsic activity of a Pt/C catalyst in the oxygen reduction reaction.