Co9S8 integrated into nitrogen/sulfur dual-doped carbon nanofibers as an efficient oxygen bifunctional electrocatalyst for Zn-air batteries

Rational design of efficient precious metal-free bifunctional electrocatalysis for the oxygen reduction and evolution reactions (ORR/OER) is highly demanded for practical applications in metal-air batteries. Herein, Co9S8 nanoparticles (NPs) encapsulated in nitrogen/sulfur dual-doped porous carbon nanofibers had been designed and synthesized by an electrospinning method with subsequent thermal annealing and denoted as Co9S8/NSC nanofibers. The as-prepared Co9S8/NSC nanofibers with high intrinsic activity and electrical conductivity exhibited excellent bifunctional oxygen electrocatalytic activity, with a half-wave potential of 0.84 V (vs. RHE) for the ORR and a potential of 1.56 V (vs. RHE) for the OER at 10 mA cm-2 current density. When Co9S8/NSC nanofibers were employed as an air electrode catalyst for rechargeable Zn-air batteries, a high energy density (997 W h kg-1), a low charge/discharge voltage gap, and an impressive long-term cycle stability (over 1000 cycles at 10 mA cm-2) were achieved.