Hierarchical Core-Shell Co2 N/CoP Embedded in N, P-doped Carbon Nanotubes as Efficient Oxygen Reduction Reaction Catalysts for Zn-air Batteries

Abstract

Projecting a cost-effective and highly efficient electrocatalyst for the oxygen reaction reduction (ORR) counts a great deal for Zn-air batteries. Herein, a hierarchical core-shell ORR catalyst (Co₂ N/CoP@PNCNTs) is developed by embedding cobalt phosphides and/or cobalt nitrides as the core into N, P-doped carbon nanotubes (PNCNTs) as the shell via one-step carbonization, nitridation, and phosphorization of pyrolyzing Co-MOF precursor. The globally N, P-doped structure of Co₂ N/CoP@PNCNTs demonstrates an outstanding electrocatalytic activity in the alkaline solution with the onset and half-wave potentials of 1.07 and 0.85 V respectively. Moreover, a Zn-air battery assembled from Co₂ N/CoP@PNCNTs as the air cathode delivers an open circuit potential of 1.49 V, a maximum power density of 151.1 mW cm^-2 and a specific capacity of 823.8 mAh kg^-1 . It is reflected that Co₂ N/CoP@PNCNTs provides a long-term durability with a slight decline of 15 h in the chronoamperometry measurement and an excellent charge-discharge stability with negligible voltage decay for 150 h at 10 mA cm^-2 in Zn-air batteries. The results reveal that Co₂ N/CoP@PNCNTs has superiority over most Co-N_x -C or Co_x P@C catalysts reported so far. The excellent catalytic properties and stability of Co₂ N/CoP@PNCNTs derive from synergistic effects between Co₂ N/CoP and mesoporous N, P-doped carbon nanotubes.

Keywords: N; P doping; Zn-air batteries; core-shell electrocatalysts; oxygen reduction reaction; synergistic effects.