Silver cluster supported on nitrogen-doped graphene as an electrocatalyst with high activity and stability for oxygen reduction reaction

•N-doped graphene anchors the Ag8 cluster to make a more active electrocatalyst.•Ag8 cluster supported on N-doped graphene facilitates the OO bond-breaking.•Binding energy of O2 on supported Ag8 cluster is within the optimal range for ORR.

An Ag8 cluster deposited on three different types of nitrogen (N)-doped graphene was studied using density functional theory calculations with empirical pair potentials (DFT-D). Among the different kinds of N-doped graphene, the pyridinic-N3 (P-N3) type can act as the best anchor position to stabilize Ag8. In addition, it is found that supported Ag8 clusters show higher activity in oxygen reduction reaction compared to unsupported clusters due to significant decrease in O2 adsorption energy and higher charge transfer to O2. Electron transfer from Ag to O2 leads to the elongation of the OO bond, which facilitates the breaking of this bond in the oxygen reduction reaction. All results suggest that N-doped graphene support can play a significant role in the chemical reactivity of a Ag8 cluster in oxygen reduction reaction.