Molecularly engineered MnN4 sites on hierarchical carbons as pH-universal oxygen reduction electrocatalysts for high-energy zinc-air battery

The development of efficient and stable oxygen reduction reaction (ORR) catalysts is critical for advancing sustainable energy technologies, particularly rechargeable zinc-air batteries (ZABs) which offer high theoretical energy density, inherent safety, and cost-effectiveness compared to other metal-air systems. However, the widespread application of ZABs is hindered by the sluggish kinetics of the air cathode ORR, and state-of-the-art Pt-based catalysts suffer from high cost, susceptibility to poisoning, and inadequate durability in neutral media. To address this challenge, non-precious metal catalysts represented by metal‑nitrogen‑carbon dopants have attracted significant attention due to their geometrically constrained coordination environments that resist hydrolytic dissociation and electronic structures capable of circumventing specific adsorption poisoning pathways. Herein, we report a molecularly engineered manganese single-atom catalyst (MnNC-0.5) synthesized via a cyano-amino coordination strategy coupled with MgO-templated pyrolysis. This approach creates well-defined Mn N 4 sites adjacent to -CN functional groups within a hierarchical porous carbon matrix. The catalyst exhibits exceptional ORR activity across the entire pH spectrum, with half-wave potentials of 0.89 V in 0.1 M KOH, 0.77 V in 0.5 M H 2 SO 4 , and 0.69 V in 0.1 M PBS. It also demonstrates remarkable stability, retaining over 90% of its initial current after 35,000 s of continuous operation. Density functional theory (DFT) calculations reveal that the adjacent -CN group electronically modulates the Mn N 4 center, optimizing the adsorption free energy of oxygen intermediates and thereby enhancing the intrinsic activity. When employed as an air cathode in a liquid ZAB, the MnNC-0.5-based device achieves a peak power density of 193.4 mW cm −2 and a high specific energy density of 1094 Wh kg Zn −1 , outperforming the Pt/C benchmark. This work provides a viable molecular-engineering strategy for designing high-performance, pH-universal ORR electrocatalysts for next-generation energy conversion and storage devices.