Surface electrochemistry of chloro(phthalocyaninato)rhodium(III) species and oxygen reduction electrocatalysis. Formation of a dimeric species

Abstract

Abstract : The deposition of Chloro(phthalocyaninato)rhodium(III) onto a highly oriented pyrolytic graphite (HOPG) electrode leads to a surface which can be organized by polarizing to potentials negative of the reduction of rhodium(III) to rhodium(II). The organized surface contains dinuclear rhodium phthalocyanine which is fairly stable in its (RhIIPc)2 oxidation state. It is reversibly oxidized to a (RhIIIPc)2 dinuclear species which decomposes slowly to monomeric RhIIIPc detected upon the surface through its electroactivity. Reduction of this mononuclear RhIIIPc back to RhIIPc leads to redimerization. The surface electrochemistry of this dynamic interplay between mononuclear and dinuclear species is explored in depth. The dinuclear (RhIIPc)2 species reacts with oxygen to form oxygen adducts which appear to be involved in both the 2-electron reduction of oxygen to hydrogen peroxide, and the 4-electron reduction to water. However these two processes proved difficult to characterize.