Uncovering the Missing Link between Molecular Electrochemistry and Electrocatalysis: Mechanism of the Reduction of Benzyl Chloride at Silver Cathodes

Herein, the traditional views that contrast the important areas of electrocatalysis and molecular electrochemistry are challenged. By extending Laviron’s seminal concept, we show that these two domains only represent idealized limits of a much broader continuum. More importantly, we show that electrochemical systems that apparently behave experimentally as if under diffusion control (i.e. systems that obey the founding molecular electrochemistry paradigm) may be controlled by electrocatalytic steps, that is, in which the activation of electroactive substrates exclusively occurs through adsorbed intermediates. This analysis is supported through quantitative experimental and theoretical investigations on the reduction of benzyl chloride at silver electrodes. At silver cathodes, the reduction wave of benzyl chloride as monitored at the usual scan rates is dramatically shifted to more positive potentials by about 0.5 V versus that at inert (e.g. glassy carbon) electrodes. This approach, which is based on the use of fast-scan cyclic voltammetry and simulations (KISSA-1D), combined with our previous results from surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) analysis, allow us to fully unravel the mechanistic origin of this dramatic effect and quantitatively validate this mechanism, which has eluded many research groups until now. In practice, this example provides a missing link between the traditional areas of electrocatalysis and molecular electrochemistry. Furthermore, it bridges the chemical areas of organometallic/inorganic catalysis and electrochemical activation by showing that the inner-sphere concept, as developed by Taube and Myers for inorganic reactions, applies perfectly to electrochemical reactions of molecular substrates