Effect of the OH functionalization on the catalytic activity of a single-atom catalyst

The existence of the hydroxyl ligand on a single-atom catalyst embedded in graphene, especially Fe(OH)-N4-C, is suggested to improve the oxygen reduction reaction (ORR) from the pristine Fe-N4-C. However, the theoretical electrocatalytic activity of the ORR process is shown to be highly dependent on the electrolyte solution and the applied electrode potential. Herein, we performed the constant-potential simulation and microkinetic modelling to investigate the mechanism of ORR on well-studied Fe(OH)-N4-C and Co(OH)-N4-C catalysts and compared them with the pristine ones, using density functional theory calculation combined with the effective screening medium method and the reference interaction site model. It was found that the Fe(OH)-N4-C and Co(OH)-N4-C have comparable ORR activities to Fe-N4-C and Co-N4-C, and the calculated limiting potentials and half-wave potentials agree with the experimental values, in contrast to the results obtained using the constant-charge method (i.e. under the neutral condition) regardless of consideration of the solvation effect. This article is part of the theme issue 'Surfaces, interfaces and heterogeneous catalysis'.