Metallic Co and FeNi alloy hybrid nanoparticles immobilized into N-doped graphene-like carbon nanosheets as an efficient bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

The development of efficient, low-cost and durable bifunctional oxygen electrocatalysts becomes a top priority for large-scale application of rechargeable Zn-air batteries (ZABs). Herein, we report the construction of durable and efficient bifunctional oxygen electrocatalyst by immobilizing metallic Co and FeNi alloy hybrid nanoparticles into N-doped, graphene-like carbon nanosheets (denoted as FeNi/Co-NCG) for rechargeable ZABs. Specifically, the N-enriched Schiff base-Co²⁺ coordination polymer (denoted as TP-Co) is first synthesized by Co²⁺-induced Schiff base reaction of 2,4,6-tris(4-aminophenylmethylamino)-1,3,5-triazine and picolinaldehyde, which is then mixed with the solvothermally generated melamine/Fe³⁺/Ni²⁺ complex followed by a two-step pyrolysis, yielding the FeNi/Co-NCG electrocatalyst. The resultant FeNi/Co-NCG electrocatalyst manifests not only the high bifunctional activity, i.e., a small potential gap (ΔE = 0.71 V) between E_j=10 (1.57 V, oxygen evolution reaction (OER) potential at a current density (j) of 10 mA cm⁻²) and E_1/2 (0.86 V, oxygen reduction reaction (ORR) half-wave potential) in 0.1 M KOH solution, but also the excellent durability. Accordingly, aqueous and solid-state rechargeable ZABs assembled with the FeNi/Co-NCG air cathode display ultralong cycle life, i.e., 1393 h at 20 mA cm⁻² for the aqueous rechargeable ZAB, and 120 h at 2 mA cm⁻² and 70 h at 5 mA cm⁻² for the solid-state rechargeable ZAB.