Distinguished Zn,Co-Nx-C-Sy active sites confined in dentric carbon for highly efficient oxygen reduction reaction and flexible Zn-air Batteries

Abstract

M-Nx-C (M stands for Fe, Co, Ni) represent a typical type of highly efficient oxygen reduction reaction (ORR) nonprecious-metal catalyst, of which the catalytic activity can be further boosted by introducing other metal or nonmetal species. However the rational design and construction of such system remains conceptually challenging and requires in-depth research both experimentally and theoretically. In this work, highly active sulfur (S)-modified Zn,Co-Nx-C-Sy bimetallic sites confined in dentric carbon are developed through a facile simultaneous coordination pyrolysis method. Such an architecture offers two fold advantages in ORR catalysis: 1) The enhanced binding between O2 and Zn-Co bimetallic site can facilitate the O-O activation and reduce the cleavage barrier of O-O bond in the step of *OOH + e-→*O + OH-; 2) the S doping can engineer the charges around Zn,Co active center, and strengthen the interaction with oxygenated species by decreasing the free energy changes of *O2 + e- + H2O→*OOH + OH- step. As a result, the as prepared Zn,Co-Nx-C-Sy exhibits outstanding electrocatalytic performance with a half wave potential 67 mv more positive than commercial Pt/C (0.893 V vs. 0.826 V), as well as excellent stability ( ~ 4.4% current loss after 20,000 s test). The material also shows promising potential as cathode catalyst in flexible Zn-air batteries.