Methane to Methanol Conversion over N-Doped Graphene Facilitated by Electrochemical Oxygen Evolution: A First-Principles Study

Direct methane oxidation to methanol is ideal for replacing the oxygen evolution reaction (OER) in artificial photosynthesis. This reaction requires less electricity and generates more valuable products than the OER. Moreover, it provides a better way to utilize abundant but inert methane. In this study, we have used density functional theory combined with a constant electrode potential model to evaluate the possibility of using abundant and low-cost N-doped graphene to catalyze this reaction. The active oxygen (*O) for rate-determining C-H activation is generated during the OER process. The results from our calculations show that this catalysis could be realized when graphene is doped with two nitrogen atoms in the vicinity of the reaction center so that long-lived *O is present and reacts to break strong methane C-H bonds. The minimum overall kinetic barrier is 0.91 eV at a potential of U = 1.10 V_SHE, which is 0.82 eV lower than that in the absence of Us. The significant barrier reduction indicates that anodic potentials play essential roles in increasing the reactivity of N-doped graphene. During C-H activation, hydrogen is transferred from methane to *O. Analyzing this step using the Intrinsic Atomic Orbitals approach, we find that it follows a hydrogen atom transfer mechanism where the proton and electron travel together. Importantly, our analysis reveals that this transfer starts with the excitation of one electron from the *O lone pair to a surface π-orbital. This excitation increases the radical character on *O, rendering it reactive to couple with the transferred hydrogen atom. Easing this excitation is expected to further improve the reactivity of *O, as demonstrated by our calculations.