Axial O-ligand induced high ORR activity over Mo and N codoped graphene: A computational mechanism study

The catalytic activity of single metal atom were effectively enhanced by different coordination environments, and the underlying improvement mechanisms are generally ascribed to the electronic structure modification by in-plane ligands. Herein, taking the recently synthesized MoNO composites modified carbon as representative, we clarified the multiple functions of axial oxygen ligand in improving the oxygen reduction activity. The active Mo atom is protruded from graphene plane due to the interaction with axial oxygen ligand, and during adsorption of oxygenates, the hanging oxygen ligand would wag to leave space and meanwhile tune the orbital orientation of Mo atom, giving rise to an optimal adsorption strength on the side in presence of oxygen ligand. The dynamic oxygen ligand may participate in the catalysis through hydrogenation reaction at the coadsorption stage with oxygen intermediate. The obtained overpotential of 0.35 V on MoN2O1-pen-gra along homolateral adsorbate evolution mechanism is comparable to recent experiments, approving the reliability of models and mechanism proposed in current study. The present results could provide some new insights into the functions of axial ligands and further guide the rational design of axial coordination to improve the catalytic performance.