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

The Kolbe reaction is one of the most classical electrochemicalreactions, which enables carboxylic acids or carboxylates to undergodecarboxylation 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 inelectrochemical reactions. Electrochemists have obtained abundantempirical evidence that the electrode materials surfaces can affectreaction paths and products, but conventional experiments have difficultyobtaining a microscopic understanding of the specific role of surfaces.In this work, we employ ab initio atomic models to simulate the Kolbe-typeoxidation reactions of acetic acid as a model reactant on Pt and graphitesurfaces from both thermodynamic and kinetic perspectives. An atomic-scaleunderstanding is presented to explain why Pt and graphite electrodesurfaces exhibit different preferences for reaction paths, and wealso reveal the joint impact of surface morphologies and adsorptionconfigurations on the kinetics of rate-limiting steps. For the surfacemorphologies, low-coordinated Pt atoms make the decarboxylation easierto happen on the Pt surface than on the graphite surface. The adsorptionconfiguration of oxidative reaction intermediates is also a determiningfactor for the energy barriers of different reaction paths on thetwo surfaces. These discoveries provide mechanistic insights intothe anodic oxidation of carboxylic acids, facilitating the understandingof microscopic electrochemical processes and the exploration of newelectrochemistry.