Uniformly Dispersed Fe Clusters on Nitrogen-Doped Carbon Aerogel as a High-Performance Cathode Catalyst for Li-O2 Batteries.

Lithium-oxygen (Li-O2) batteries are a compelling next-generation energy storage candidate owing to their ultrahigh theoretical specific energy, but their practical deployment is critically limited by sluggish cathodic oxygen reduction/evolution kinetics, severe polarization, and poor cyclability. Here, we design a composite catalyst consisting of ultrasmall iron clusters uniformly anchored on a three-dimensional nitrogen-doped carbon aerogel (Fe@NC). The material is synthesized via bidirectional freeze-drying followed by high-temperature reduction carbonization using chitosan, cellulose nanocrystals, and zinc acetate; sublimation of zinc during pyrolysis effectively suppresses iron aggregation, yielding highly dispersed Fe0 clusters of ~10 nm while preserving the aerogel's hierarchical porous architecture rich in pyridinic and pyrrolic N species. Electrochemical tests show that Fe@NC delivers a deep-discharge specific capacity of 18,000 mAh/g, substantially outperforming pristine carbon aerogel and commercial Ketjen black, and maintains stable cycling over 280 cycles at 500 mAh/g. Microscopic and spectroscopic analyses confirm that Fe@NC promotes uniform, fine-particle Li2O2 deposition without pore blockage and enables its complete reversible decomposition upon charging, effectively mitigating electrode passivation. This work demonstrates that the synergistic combination of carbon aerogel mass-transport benefits and iron cluster catalytic activity provides a viable, scalable route to high-performance Li-O2 battery cathodes.