Ultramicroporous Carbon Aerogel-Supported Iron Single-Atom Catalysts Toward Efficient pH-Universal Oxygen Reduction and Acidic/Alkaline Zinc–Air Batteries

Development of highly efficient nonprecious metal-based oxygen reduction catalysts, capable of operating within a broad pH range, has remained a great challenge in electrocatalysis. Herein, ultramicroporous carbon aerogel-supported iron single-atom catalysts (MPCA/Fe) are synthesized using a chitosan hydrogel precursor, with zinc species acting as a sacrificial template. Structural characterizations reveal that the produced ultramicropores effectively facilitate the anchoring of Fe single atoms within the carbon aerogel. The resulting MPCA/Fe composites exhibit a remarkable activity and stability toward the oxygen reduction reaction, featuring a half-wave potential of +0.93, +0.82, and +0.79 V in alkaline, neutral, and acidic media, respectively. Computational studies based on density functional theory calculations indicate that FeN4 sites embedded within the ultramicropores possess moderate *OH adsorption energy, leading to excellent catalytic performance. As MPCA/Fe also exhibits apparent electrocatalytic activity towards the oxygen evolution reaction, a zinc–air battery is assembled with the MPCA/Fe as the cathode catalyst, which delivers an open-circuit voltage (OCV) of 1.50 V and a peak power density of 240.8 mW cm–2 and excellent durability during 1600 charge–discharge cycles. When MPCA/Fe is assembled into an acid/alkali-mixed zinc–air battery, the device enables an exceptionally high OCV of 2.20 V and a discharge voltage of 2.07 V at a current density of 5 mA cm–2. Results from this study offer an effective strategy for the development of high-performance pH-universal oxygen reduction electrocatalysts.