Engineering biomass into advanced carbon-based materials for Zn-air batteries

• • Biomass-derived Fe-N-C catalysts achieve half-wave potentials (E₁/₂) of 0.80–0.85 V vs. RHE in alkaline media, rivaling commercial Pt/C (E₁/₂ ≈ 0.84 V), but with a cost reduction exceeding 90% due to abundant, renewable precursors. Industrial impact: enables affordable ORR cathodes for stationary ZABs, though durability remains below 5,000 cycles. • • Co₃O₄ nanoparticles hydrothermally dispersed on nitrogen-doped hierarchically porous carbon (from biomass) exhibit a bifunctional potential gap (ΔE = E_OER@10 − E_ORR@−3) of 0.75–0.85 V, outperforming precious-metal benchmarks (ΔE > 1.0 V). This narrow gap is critical for rechargeable ZABs, reducing charge-discharge voltage hysteresis by 0.2–0.3 V. • • Fe single-atom sites coupled with Fe₂O₃ clusters on porous carbon deliver ORR mass activity of 10–20 A g⁻¹ at 0.80 V vs. RHE, a 3–5 fold enhancement over Fe-free N-doped carbons. The synergy between atomic Fe-N₄ and Fe₂O₃ clusters boosts O₂ adsorption and reduces peroxide yield below 5%, addressing the degradation pathway in ZABs. • • Flexible quasi-solid-state ZABs using cellulose/aramid nanofiber-derived carbon aerogels achieve areal capacities of 5–10 mAh cm⁻² and power densities of 50–100 mW cm⁻², with stable operation over 100–200 hours (300–600 cycles) at 5–10 mA cm⁻². These metrics meet the requirements for wearable electronics, but mechanical robustness under 30% strain requires further optimization.