Design and synthesis of self-supporting FeCoNi- and N-doped carbon fibers/nanotubes as oxygen bifunctional catalysts for solid-state flexible Zn-air batteries

Developing effective bifunctional electrocatalysts with efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) capabilities is critical to advancing rechargeable zinc-air batteries. This study harnessed the properties of organic salts in polymer solutions via electrospinning to synthesize self-supporting flexible bifunctional electrocatalysts, termed FeCoNi flexible carbon nanofibers (FeCoNi FCNFs). These catalysts benefitted from the secondary growth of FeCoNi- and N-doped carbon nanotubes on fiber surfaces, generating numerous metal-nitrogen-carbon (M−N−C) ORR active sites and FeCoNi alloy-based OER active sites. At 10 mA/cm2, FeCoNi FCNFs exhibited a half-wave potential of 0.92 V for ORR and 1.64 V for OER. Density functional theory calculations based on first principles demonstrated that FeCoNi FCNFs possessed superior bifunctional activity. Moreover, rechargeable liquid Zn-air batteries constructed with this catalyst achieved a high peak power density and exceptional cycling stability lasting over 630 h. Additionally, a solid-state wearable battery using this catalyst displayed outstanding cycle stability, continuously cycling for over 27 h. This research offers both insight and a fresh approach for designing efficient, cost-effective bifunctional solid-state or liquid zinc-air batteries.