Structure-performance relations for N- and Fe-N-doped carbons derived from ZIF-8 in near-neutral Zn-air batteries

Zinc-air batteries (ZABs) with non-alkaline electrolytes can offer enhanced stability and safety compared to their alkaline counterparts, addressing challenges like irreversible CO₂ uptake and uneven zinc deposition. However, their adoption is hindered by sluggish kinetics of oxygen reduction and evolution reactions (ORR and OER). This study explores the structure-performance relationships of nitrogen-doped and Fe-N-doped carbon catalysts derived from zeolitic imidazolate framework ZIF-8 in non-alkaline ZABs. Using ZIF-8 particles of varying sizes (50 nm, 200 nm, 1 µm) and systematically doping with up to 2 wt. % of Fe, we identify critical parameters that optimize the catalytic performance. Doping with just ∼0.03–0.2 wt. % of iron significantly improves the ORR kinetics, while smaller particle sizes lower the overpotentials for both ORR and OER. Optimal materials achieve roundtrip energy efficiency of 75–77 % at 1 mA cm⁻² and peak power density of ∼30 mW cm⁻². At the same time, excessive Fe doping (>1 wt. %) or larger particles reduce the charge/discharge performance. These findings underscore the importance of balancing the particle size and Fe content to develop high-performance non-alkaline ZABs, paving the way for cost-effective and sustainable energy storage solutions.