(Invited) Understanding Inner-Sphere Electrochemical Reactions at the Molecular Level

Abstract

Interfacial ET processes can be broadly classified as either outer-sphere or inner-sphere. For outer-sphere reactions, the electrode serves only as a chemically inert source or sink of electrons, whereas, for inner-sphere reactions, ET accompanies bond rearrangement at the electrode surface. While outer-sphere ET is well-described by Marcus-type models, there currently exists no analogous molecular-level understanding of inner-sphere ET at electrode surfaces, despite the central role of these reactions in virtually all electrochemical technologies, ranging from supercapacitors to batteries to fuel cells and electrolyzers. This persistent knowledge gap results from the inability to characterize or control the chemistry of metallic electrode surfaces at the molecular level, making it difficult, if not impossible, to unambiguously correlate the thermodynamics and kinetics of inner-sphere reactions to the local structure of the surface site undergoing bond rearrangement. This talk will highlight a strategy developed in our group for conjugating well-defined molecular active sites to graphitic electrodes. Electrochemical and spectroscopic data indicate that these graphite-conjugated molecules do not behave like their solution-phase analogues, but rather as metallic active sites that proceed exclusively through inner-sphere ET reaction mechanisms. This new class of functional interfaces enables investigations of inner-sphere interfacial ET with an unprecedented level of detail.