First-Principles Investigation of the Unique Role of Anode Surfaces in Organic Electrochemical Reactions

The Kolbe reaction is one of the most classical electrochemical
reactions, which enables carboxylic acids or carboxylates to undergo
decarboxylation processes via anodic oxidation, forming dimeric alkanes.
The reaction could be influenced by many factors separately or synergistically,
and changing a single factor may completely change the reaction path.
Platinum (Pt) and graphite are common electrode materials used in
electrochemical reactions. Electrochemists have obtained abundant
empirical evidence that the electrode materials surfaces can affect
reaction paths and products, but conventional experiments have difficulty
obtaining a microscopic understanding of the specific role of surfaces.
In this work, we employ ab initio atomic models to simulate the Kolbe-type
oxidation reactions of acetic acid as a model reactant on Pt and graphite
surfaces from both thermodynamic and kinetic perspectives. An atomic-scale
understanding is presented to explain why Pt and graphite electrode
surfaces exhibit different preferences for reaction paths, and we
also reveal the joint impact of surface morphologies and adsorption
configurations on the kinetics of rate-limiting steps. For the surface
morphologies, low-coordinated Pt atoms make the decarboxylation easier
to happen on the Pt surface than on the graphite surface. The adsorption
configuration of oxidative reaction intermediates is also a determining
factor for the energy barriers of different reaction paths on the
two surfaces. These discoveries provide mechanistic insights into
the anodic oxidation of carboxylic acids, facilitating the understanding
of microscopic electrochemical processes and the exploration of new
electrochemistry.