Single iron atoms stabilized by microporous defects of biomass-derived carbon aerogels as high-performance cathode electrocatalysts for aluminum-air batteries

Atomically dispersed metal catalysts have demonstrated superb electrocatalytic activity because of optimal atom efficiency. However, a rational design of low-cost, high-performance single atom catalysts remains a great challenge due to the elusive chemical reactions of the formation of metal active sites. In this work, biomass hydrogel is prepared as a template for mass production of three-dimensional carbon aerogel-supported single metal atom catalysts. By tailoring the structure of the hydrogel templates, the obtained carbon aerogels exhibit an increase of microporous defects which capture and stabilize isolated metal atoms and minimize aggregation during pyrolysis. Extended X-ray absorption fine structure, Mossbauer spectroscopy, and nitrogen adsorption-desorption isotherm measurements indicate that single metal centers of FeN4 are formed and embedded within the hierarchical porous carbon frameworks. The obtained composites exhibit outstanding catalytic activity towards oxygen reduction in alkaline media, with a high onset potential of +1.05 V and half-wave potential of +0.88 V, as well as excellent durability. Remarkably, when the carbon aerogels are used as the cathode catalyst in an aluminum-air battery, the battery achieves an ultrahigh open-circuit voltage of 1.81 V, large power density of 181.1 mW cm(-2) and stable discharge voltage of 1.70 V at 20 mA cm(-2), markedly better than those with commercial Pt/C as the cathode catalyst.