Co nanoparticle embedded in atomically-dispersed Co-N-C nanofibers for oxygen reduction with high activity and remarkable durability

Although Co and N codoped carbon (Co-N-C) materials could be served as the promising oxygen reduction reaction (ORR) electrocatalysts, they still suffer from unsatisfactory catalytic activity, especially in acidic environment. Herein, we report that the construction of Co nanoparticles embedded within highly porous, atomically-dispersed Co-N-C nanofibers catalyst not only significantly improves the ORR activity with a half-wave potential (E-1/2) of 0.778 V/RHE, but also achieves the remarkable durability with only similar to 9 mV decay of E-1/2 after a 10000-cycle accelerated durability test between 0.6 and 1.1 V. Both aberration-corrected scanning transmission electron microscope and X-ray adsorption spectroscopy confirm the existence of Co single atoms in the carbon nanofibers. Density functional theoretical calculation reveals that the introduction of Co core nanoparticle lowers the d band center of surface Co atoms in graphite shells and makes the free energy diagrams of the ORR process on Co-N-C shell more close to the ideal case, thus boosting the catalytic performance. Proton exchange membrane fuel cell integrated with as-prepared catalyst delivers a peak power density of 0.42Wcm(-2) together with excellent stability after 100 h operation. This study provides an ideal perspective to develop highly efficient and durable Co-based catalyst for the oxygen reduction.