Spatial-five coordination promotes the high efficiency of CoN4 moiety in graphene-based bilayer for oxygen reduction electrocatalysis: A density functional theory study

The searching of highly efficient catalysts for oxygen reduction reaction(ORR) has attracted particular attention. In this work, we construct the graphene-based bilayers BG/X that consists by the CoN4embedded graphene as the upper layer and the X modified graphene as the bottom layer(X = Si, P, S). The interfacial bonding between CoN4site and the X dopant is spontaneously formed due to the strong pd hybridization, which changes the Co ligand from the planar-four N4coordination into spatial-five N4+X one. The additive glue atom weakens too strong adsorptions of the ORR intermediates on CoN4site and thereby improves the ORR activities in comparison with the monolayer counterpart. From the free energy profiles, the overpotentials η are 0.47, 0.49 and 0.45 V for BG/Sia, BG/Paand BG/Sa, respectively,being comparable to that of state-of-the-art Pt material. Besides, the kinetic barriers for the bilayers are less than 0.75 eV, an indicative of the room temperature activity. Furthermore, the combination of thermodynamic and kinetic analysis ensures the preference of 4e--OOH associative mechanism over 2e--H2O2mechanism, being beneficial for membrane stability against the H2O2corrosion. Therefore,the graphene-based bilayers deliver the high efficiencies for oxygen reduction electrocatalysis.Therefore, the interfacial bonding in the graphene-based bilayers provides an interesting strategy to suppress the poisoning phenomenon for the material design from atom scale.