High performance and bifunctional cobalt-embedded nitrogen doped carbon/nanodiamond electrocatalysts for oxygen reduction and oxygen evolution reactions in alkaline media

Abstract

A bifunctional noble metal-free catalyst with a cobalt-embedded nitrogen doped graphitized carbon shell covering a nanodiamond (ND) core (Co–N–C/ND) is synthesized. The resulting Co–N–C/ND exhibits excellent catalytic activities for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media. The average electron transfer number of ORR on the Co–N–C/ND is 3.82 between −0.4 and −0.7 V (vs. Hg/HgO), indicating a near four-electron transfer mechanism for ORR. Moreover, the catalytic activity of the Co–N–C/ND for ORR is comparable to the 20 wt% Pt reference catalyst supported on carbon black. The OER onset potential on the Co–N–C/ND is 0.43 V (vs. Hg/HgO) and the current density at 0.7 V is 3.19 mA cm−2, demonstrating excellent catalytic activity for OER. In comparison to the Co–N–C derived from carbon black, the Co–N–C/ND exhibits better durability. The superior electrocatalytic performance of the Co–N–C/ND could be attributed to the synergistic effect of the Co–N moieties in the carbon shell and the high stability could be ascribed to the ND core.