Aggregation-Induced Improvement of Catalytic Activity of Metalfullerene-Based Surfactants Used in Water Splitting Reaction

An inherent paradigm of molecular compounds used in homogeneous catalysis is that maximum performance requires maximum dispersion, and that any form of aggregation results in a loss of activity. We here present a new concept based on surfactants with functional heads, which become better catalysts when they aggregate. The head group of the surfactants is composed of a diethylenetriamine-functionalized fullerene, which coordinates Co II ions. This system is applied as an electrocatalyst for the water-splitting reaction. Detailed electrochemistry studies were performed at concentrations below and above the critical aggregation concentration (cac), when 150 nm sized vesicles are formed. While isolated surfactant molecules represent only moderately active catalysts, drastic improvement in the hydrogen evolution (HER) as well as in the oxygen evolution reactions (OER) were detected for the vesicular structures. Self-organization of the surfactants leads to an increase in turnover frequencies of up to 1300% (HER). We show that the strongly beneficial effect of aggregation arises from the favorable alignment of individual molecules, thus facilitating intermolecular charge transfer processes in the vesicles.