An advantage combined strategy for preparing bi-functional electrocatalyst in rechargeable zinc-air batteries

Abstract The development of rechargeable zinc-air batteries requires the rational construction and exploration of robust and cost-effective bi-functional cathode catalysts to replace common noble metal-based ones for efficient oxygen reduction/evolution reactions (ORR and OER). In this study, a new kind of hierarchically ordered porous carbon co-doped by FeCo alloy nanoparticles and FeN2 moiety was synthesized via a hard-templated molding and two-step pyrolysis strategies. Notably, rational modulation of FeCo and FeN2 endows maximal synergistic effect between the intrinsic activity of FeCo alloy nanoparticles and the atomically dispersed FeN2 moieties for OER and ORR, respectively. Furthermore, the ordered hierarchical porous structure carbon matrix possessing a large surface area can accelerate mass transfer, enlarge the contact area with electrolyte, and expose more active sites which buried deeply in the material. As a result, the obtained FeCo/FeN2/NHOPC exhibited remarkable bi-functional catalytic activity in terms of a more positive half-wave potential (0.86 V) compared with Pt/C (0.84 V) for ORR in alkaline medium, a low overpotential of 340 mV for OER in the same condition, and the reversible oxygen electrode index of 0.71 V. Moreover, when served as a cathode catalyst in a home-made rechargeable zinc-air battery, the material performs the superior reactive activity with a high energy density of 810.3 mWh gZn−1, a peak power density of 128.7 mW cm−2, and excellent stability over 120 cycles at 10 mA cm−2 without apparent degradation. Importantly, the advantage combined strategy proposed in this work indicates an auspicious direction for synthesizing high-performance bi-functional catalysts.