Core-shell structured metal organic framework materials derived cobalt/iron–nitrogen Co-doped carbon electrocatalysts for efficient oxygen reduction

Abstract

Homogeneous dispersion of active sites and abundant pore structure for non-precious metal electrocatalysts are favorable for the oxygen reduction reaction (ORR) activity. Herein, a nitrogen-doped carbon core supported CoFe alloy-nitrogen co-doped carbon shell nanopolyhedron (NC@CoFe,N–CNP) electrocatalyst, which has rich pore structure and uniformly distributed active sites, is prepared through a facile thermal conversion of a ZIF-8 core and Fe,Co-ZIF shell composite precursor (ZIF-8@Fe,Co-ZIF) without any post-treatments. The existence of ZIF-8 core can maintain the structure of the ZIF-8@Fe,Co-ZIF composite controllable, avoiding the damage to the pore structure for fast mass transfer during pyrolysis. Meanwhile, the bi-metal iron and cobalt co-doping shell is more conducive for uniform dispersion of CoFe alloy particles than single one due to the interval effects, which can create various active sites and efficiently promote the ORR activity. As expected, the optimal NC@CoFe,N–CNP electrocatalyst exhibits an excellent catalytic activity with a high onset potential and half-wave potential (0.970 V and 0.865 V) compared to commercial Pt/C (0.934 V and 0.846 V). The kinetic current density of NC@CoFe,N–CNP reached to 7.99 mA cm−2, which is higher than Pt/C (5.14 mA cm−2) at 0.85 V. Furthermore, the NC@CoFe,N–CNP electrocatalyst demonstrates better electrochemical stability and anti-poisoning ability.