Study on the Mechanism of Oxygen Reduction Reaction on Graphene with CoNx Centers
The oxygen reduction reaction(ORR)catalytic mechanism of two graphene(CoNx-G)catalysts containing CoNx(x=2,3)centers was investigated using theoretical computational methods.On both catalysts,the lowest-energy reaction pathway for ORR follows the same mechanism:the O2(ads)molecules are first hydrogenated and reduced to OOH(ads),which then undergoes hydrogenation and dissociation to produce two OH(ads)molecules,and finally the OH(ads)continues to hydrogenate and reduce to form water.The key difference lies in the fact that the reduction of OH(ads)to H2O(ads)on the CoN2-G structure serves as the highest energy barrier(HEB)step of the entire pathway,whereas on the CoN3-G structure,the reduction of O2(ads)to OOH(ads)is the HEB.Compared to CoN2-G,CoN3-G exhibits a lower HEB,a better structural symmetry,more negative formation energy,and maintains a positive charge on the Co centers throughout the ORR process,which facilitates the activation of oxygen-containing intermediate.Consequently,CoN3-G shows a better ORR catalytic performance than CoN2-G,which is attributed to the optimization of the electronic structure of the Co sites and the enhancement of system stability through the coordination of three N atoms.
CoNx-G catalystscatalytic mechanismreaction barrieroxygen reduction reactiondensity functional theory
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