A multi -scale model of the oxygen reduction reaction on highly active graphene nanosheets in alkaline conditions

A multi-scale model based on a mean field approach, is proposed to describe the ORR mechanism on N-GN catalysts in alkaline media. The model implements activation energies calculated with Density Functional Theory (DFT) at the atomistic level, and scales up them into a continuum framework describing the cathode/electrolyte interface at the mesoscale level. The model also considers mass and momentum transports arising in the region next to the rotating electrode for all ionic species and O-2; correction of potential drop and electrochemical double-layer capacitance. Most fitted parameters describing the kinetics of ORR elementary reactions are sensitive in the multi-scale model, which results from the incorporation of activation energies using the mean field method, unlike single-scale modelling Errors in the deviations from activation energies are found to be moderate, except for the elementary step (2) related to the formation of O-2ads, which can be assigned to the inherent DFT limitations. The consumption of O-2ads to form OOHads is determined as the rate-determining step as a result of its highest energy barrier (163.10 kJ mol(-1)) in the system, the largest error obtained for the deviation from activation energy (28.15%), and high sensitivity. This finding is confirmed with the calculated surface concentration and coverage of electroactive species. (C) 2016 Elsevier B.V. All rights reserved.