Bifunctional Carbenium Dications as Metal-Free Catalysts for the Reduction of Oxygen

Abstract

The development of catalysts for the oxygen reduction reaction is a coveted objective of relevance to energy research. This study describes a metal-free approach to catalyzing the reduction of O₂ into H₂O₂, based on the use of redox-active carbenium species. The most active catalysts uncovered by these studies are the bifunctional dications 1,8-bis(xanthylium)-biphenylene ([<b>3</b>]²⁺) and 4,5-bis(xanthylium)-9,9-dimethylxanthene ([<b>4</b>]²⁺) which promote the reaction when in the presence of decamethylferrocene and methanesulfonic acid. Electrochemical studies carried out with [<b>4</b>]²⁺ suggest the intermediacy of an organic peroxide that, upon protonation, converts back into the starting dication while also releasing H₂O₂. Kinetic studies point to the second protonation event as being rate-determining.