Active oxygen promoted electrochemical conversion of methane on two-dimensional carbide (MXenes): From stability, reactivity and selectivity

Abstract

The electrochemical oxidation of methane is promising under mild conditions, while the Faraday efficiency is restricted at low temperatures due to very considerable required overpotentials activating the parasitic formation of oxygen. Herein, by means of large-scale density functional theory (DFT) computations, we systematically explored the electrochemical methane conversion promoted by active oxygen (O*) on 66 two-dimensional carbides (MXenes). Most MXenes are stabilized with O-terminated surface under external potential. Through the established OER activity volcano map, we showed that the materials on the right side of the volcano (corresponding to ΔEOH*–ΔEO* > −1.80 eV) satisfy the stability condition of O*. Taking into account the CH activation, we presented that there is a trade-off between the stability of O* and the reactivity toward CH activation, where TaHf2C2O2 and CrHf2C2O2 can be the promising materials for electrochemical methane conversion with a low energy barrier (<1 eV) for CH activation while inhibiting oxygen evolution. Furthermore, we found that the p-band center of O* is an effective descriptor for catalyst design in terms of stability and reactivity. And we showed that the selectivity on the screened MXenes varies under different potentials, mainly oxygenated derivatives, which stems from more metal-O* bonding orbital filling at the active site. These results demonstrate the application potential of MXenes for electrochemical conversion of methane and provide a feasible strategy for rational design and rapid screening of efficient catalysts.