Molten salt-assisted gasification unlocks graphitic nitrogen dominated porous carbons from biomass for high-performance zinc-air batteries.

Efficient, durable, and low-cost catalysts for the oxygen reduction reaction (ORR) are critical for advancing clean energy technologies such as zinc-air batteries (ZABs). Nitrogen-doped carbons are promising alternatives to platinum, but their performance remains limited by the poorly understood roles of different nitrogen (N) configurations, particularly pyridinic versus graphitic N. Here, we report a multiple gasification-induced strategy that integrates ZnCl2 molten salts with C3N5 decomposition to simultaneously tailor porous carbon architectures and N species during pyrolysis. Using rush biomass (Juncus effusus) as a renewable precursor, ZnCl2 functions as both template/etchant, generating hierarchical porous spheres, and promoter, stabilizing graphitic N. Concurrently, N-rich intermediates from C3N5 enhance doping efficiency and facilitate in situ pore formation. The resulting N-rich hierarchical porous carbon spheres (NHPCS) exhibit high surface area, optimized pore networks, and abundant graphitic N sites. Density functional theory calculations demonstrate that graphitic N provides intrinsically superior ORR activity compared to pyridinic or pyrrolic N. Experimentally, NHPCS deliver a half-wave potential (E1/2) of 0.890 V and a limiting current density of 5.61 mA cm-2, outperforming commercial Pt/C catalysts. When applied as the cathode in ZABs, NHPCS achieve a high power density of 150.4 mW cm-2. This work establishes a scalable biomass-to-catalyst pathway and rational design principle for next-generation ORR catalysts.