N, S-codoped graphene supports for Ag-MnFe2O4 nanoparticles with improved performance for oxygen reduction and oxygen evolution reactions

Heterogeneous nanoparticles with synergistic effects between different composites are potential catalysts with bifunctional catalytic activity for oxygen reduction (ORR) and oxygen evolution reaction (OER). Herein, heteroatoms such as N and S are doped into graphene substrates to improve catalytic activity and structural stability of Ag-MnFe 2 O 4 nanoparticles. Interestingly, these particles keep a primarily heterogeneous structure for their assembly on N, S-codoped graphene (NSG), while Ag domains shrink on S-doped graphene (SG) or N-doped graphene (NG). Subsequently, Ag-MnFe 2 O 4 /NSG shows the best bifunctional catalytic activity due to the improved stability of Ag-MnFe 2 O 4 NPs on NSG and enhanced bonding energy between supports and particles. The Koutecky-Levich plots confirm a major four-electron reaction pathway for the ORRs on Ag-MnFe 2 O 4 /NSG. Meanwhile, Ag-MnFe 2 O 4 /NSG exhibits higher stability and better methanol tolerance than commercial Pt/C. Therefore, Ag-MnFe 2 O 4 /NSG with bi-functional catalytic activity for ORR and OER is a promising non-Pt catalyst candidate.