Fundamental insight into electrochemical oxidation of methane towards methanol on transition metal oxides

Electrochemical oxidation of CH4 is known to be inefficient in aqueous electrolytes. The lower activity of methane oxidation reaction (MOR) is primarily attributed to the dominant oxygen evolution reaction (OER) and the higher barrier for CH4 activation on transition metal oxides (TMOs). However, a satisfactory explanation for the origins of such lower activity of MOR on TMOs, along with the enabling strategies to partially oxidize CH4 to CH3OH, have not been developed yet. We report here the activation of CH4 is governed by a previously unrecognized consequence of electrostatic (or Madelung) potential of metal atom in TMOs. The measured binding energies of CH4 on 12 different TMOs scale linearly with the Madelung potentials of the metal in the TMOs. The MOR active TMOs are the ones with higher CH4 binding energy and lower Madelung potential. Out of 12 TMOs studied here, only TiO2, IrO2, PbO2, and PtO2 are active for MOR, where the stable active site is the O on top of the metal in TMOs. The reaction pathway for MOR proceeds primarily through *CHx intermediates at lower potentials and through *CH3OH intermediates at higher potentials. The key MOR intermediate *CH3OH is identified on TiO2 under operando conditions at higher potential using transient open-circuit potential measurement. To minimize the overoxidation of *CH3OH, a bimetallic Cu2O3 on TiO2 catalysts is developed, in which Cu reduces the barrier for the reaction of *CH3 and *OH and facilitates the desorption of *CH3OH. The highest faradaic efficiency of 6% is obtained using Cu-Ti bimetallic TMO.

Understanding Attenuated Solvent Reorganization Energies near Electrode Interfaces

This manuscript studies the position-dependent profile of Marcus-like outer-sphere reorganization energy near electrode interfaces. We establish the relation between the reorganization energy and the fluctuation in the Madelung potential of redox ions in the electrolyte. The distribution of such potential narrows significantly within the screening length of the electrode, leading to the minimization of electron transfer barrier. In addition, we present a statistical field model that can capture the attenuation of reorganization energy, indicating the generality of this effect near electrode interfaces regardless the molecular details.

Understanding Attenuated Solvent Reorganization Energies near Electrode Interfaces

This manuscript studies the position-dependent profile of Marcus-like outer-sphere reorganization energy near electrode interfaces. We establish the relation between the reorganization energy and the fluctuation in the Madelung potential of redox ions in the electrolyte. The distribution of such potential narrows significantly within the screening length of the electrode, leading to the minimization of electron transfer barrier. In addition, we present a statistical field model that can capture the attenuation of reorganization energy, indicating the generality of this effect near electrode interfaces regardless the molecular details.

Extended layer-by-layer Madelung potential analysis of layered oxyhalide photocatalysts and other layered systems

Extended layer-by-layer Madelung analysis was developed and applied to various layered materials to reveal the contribution of distant layers to Madelung site potential.