Density-Functional-Theory Calculation Analysis of Active Sites for Four-Electron Reduction of O2 on Fe/N-Doped Graphene

Abstract

Nanocarbons doped with nitrogen (N) and/or metal-N coordination structures hold great promise in replacing Pt for catalyzing the oxygen reduction reaction (ORR) in fuel cells. The lack of clear views on the natures of ORR active sites in these materials has hindered the progress in reducing their activity gap to Pt through a rational desire of doping structures. Using 14 types of N and Fe–N doping structures in graphene as model systems, systematic density-functional-theory (DFT) calculations are performed within a unified electrochemical thermodynamic framework and the same reaction mechanism to gain insights into ORR active sites in doped nanocarbons. Scaling relations are obtained between the calculated adsorption free energy of key ORR intermediates at surface sites associated with various graphene doping structures. Reaction free energy analysis indicates that the proton–electron transfer coupled O2 adsorption and/or reduction of adsorbed hydroxyl group (*OH) are the activity-determining steps in the...