Role of Graphite Felt Electrode and Electron Delocalization of Cinnamate Ester in Electrochemical Hydrogenation Reaction

Abstract

The unique tunability and chemoselectivity of electrochemistry makes it a useful tool in exploring new synthetic organic reactions under mild conditions. The relevant reaction paths and especially the interfacial interactions of the reactive species and the electrode are rarely understood. From the DFT calculations of the possible homogeneous reaction paths of hydrogenation of four different cinnamate esters, the protonation step is found to be the rate-limiting step with a relatively high energy barrier (1.70–2.19 eV). The graphite felt electrode is characterized by experimental measurements, implying that vacancy or N-doping carbon defects on the surface of graphite felt are potential active sites for electrochemical reactions. It is found from DFT calculations that the vacancy and N-doping in electrodes is conducive to NH3 adsorption, which is indeed a reverse reaction of nitrogen reduction reaction to produce protons. Along with homogeneous reaction in the solution, electrode participation could both stabilize the active reaction intermediates with remarkable adsorption energies of 2.43 eV and have a limiting potential of 1.54 V, lower than that without the consideration of the electrode. The difference between the usages of different hydrogen sources, NH3 versus H2O, is rationalized by the larger binding strength of oxygen in H2O at the surface defect and the difficulty in the release of a proton.