Adsorption and Electron‐Transfer Mechanisms of Ferrocene Carboxylates and Sulfonates at Highly Oriented Pyrolytic Graphite

Abstract

AbstractFerrocene derivatives are considered as representative outer‐sphere redox couples that do not specifically interact with the electrode surface. It, however, is highly challenging to unambiguously prove their outer‐sphere character experimentally. Herein, we employ quantitative cyclic voltammetry to assess whether ferrocene carboxylates and sulfonates mediate only outer‐sphere electron transfer (ET) at highly oriented pyrolytic graphite (HOPG). We find voltammetrically that only reduced forms of ferroceneacetate, ferrocenecarboxylate, and ferrocenesulfonate are specifically adsorbed on the HOPG surface to mediate outer‐sphere ET without inner‐sphere ET, which requires the adsorption of both reduced and oxidized forms of a redox couple. By contrast, no voltammetric feature of adsorption is observed for 1,1′‐ferrocenedicarboxylate and 1,1′‐ferrocenedisulfonate to prevent us from identifying the unique mechanism among outer‐sphere ET, inner‐sphere ET, and both owing to the Laviron‐Amatore paradox.