Electric Double Layer Effect on the Outer-Sphere Benzyl Halides Electro-Reduction Mechanism

Electrocatalytic reduction of organic halides and subsequent carboxylation are
promising methods for the valorization of CO2 as a C1 source in synthetic organic chemistry.
The reaction mechanism underlying the selectivity and reduction mechanism of benzyl halides
is highly dependent on the nature of the electrode material as well as the processes,
composition, and structure of the liquid phase at the electrode−solution interface. Herein, we
present a computational study on the influence of the electric double layer (EDL) on the
activation of benzyl halides at different applied potentials over the Au (111) cathode. Using a
multiscale modeling approach, we demonstrate that, under realistic electrocatalytic conditions,
the formation of a dense EDL over the cathode hampers the diffusion of benzyl halides toward
the electrode surface. A combination of classical molecular dynamics simulations and density
functional theory calculations reveals the most favorable benzyl halide electro-carboxylation
pathway over the EDL that does not require direct substrate adsorption to the cathode surface.
The dense EDL promotes the dissociative reduction of the benzyl halides via the outer-sphere
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electron transfer from the cathode surface to the electrolyte. Such a reduction mechanism results in a benzyl radical intermediate,
which is then converted to benzyl anions in the EDL via an additional electron transfer step.