S, N co-doped carbon nanotubes coupled with CoFe nanoparticles as an efficient bifunctional ORR/OER electrocatalyst for rechargeable Zn-air batteries

The development of efficient and cost-effective bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for the commercialization of rechargeable metal-air batteries. Herein, the pyrolysis of a precursor containing g-C3N4, thiourea, cobalt chloride and ferric chloride was used to fabricate S, N co-doped carbon nanotubes functionalized with Co3Fe7 alloy nanoparticles (CoFe/S-N-C). The obtained CoFe/S-N-C catalyst exhibited an ORR half wave potential of 0.855 V (vs. RHE) in 0.1 M KOH, outperforming a commercial Pt/C catalyst (E1/2 = 0.844 V). The catalyst also demonstrated superior OER catalytic activity (1.588 V at 10 mA cm−2) relative to RuO2 in 0.1 M KOH, thus displaying outstanding bifunctional ORR and OER activity. A rechargeable Zn-air battery fabricated using CoFe/S-N-C shows good very performance (maximum power density of 120 mW cm−2 with a specific capacity of 814 mAh g−1) which was superior to a Zn-air battery fabricated using Pt/C and RuO2 as ORR and OER catalysts (92 mW cm−2 and 787 mAh g−1, respectively). Further, the fabricated battery using CoFe/S-N-C showed good stability, offering a discharge voltage ∼ 1.10 V and a recharge voltage ∼ 2.15 V at 10 mA cm−2 over 300 cycles, evidence of the durability of the CoFe/S-N-C catalyst.