Biomass-derived supramolecular engineering of N-doped porous Ni-Fe/carbon for efficient bifunctional oxygen electrocatalysis.

Developing efficient, low-cost bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucial for zinc-air (Zn-air) batteries. Herein, we report a defect-rich Ni-Fe/lignin-derived nitrogen-doped carbon (LNC) catalyst synthesized via a supramolecular assembly-pyrolysis strategy using ammonium-oxidized lignin, melamine, and ellagic acid. The supramolecular network formed through hydrogen bonding, π-π stacking, and Lewis acid-base interactions enables the uniform dispersion of Fe and Ni species while suppressing metal aggregation during carbonization. Consequently, a hierarchical porous nitrogen-doped carbon framework containing atomically dispersed Ni-Nx/Fe-Nx coordination sites and crystalline NiFe alloy nanoparticles is formed. The optimized Ni1Fe1/LNC-1000 catalyst delivers a high ORR kinetic current density of 13.75 mA cm-2 at 0.80 V, a low OER overpotential of 330 mV at 10 mA cm-2, and a small ∆E of 0.74 V, outperforming commercial Pt/C for ORR and RuO2 for OER. The assembled Zn-air battery exhibits a high specific capacity of 783.8 mAh g-1 and a peak power density of 159 mW cm-2. Operando Raman and in situ Fourier-transform infrared (FTIR) analyses provide direct evidence for the dynamic evolution of oxygenated intermediates (*O2, *OOH, and *OH) under operating conditions. Meanwhile, density functional theory (DFT) calculations reveal that the optimized electronic structure of the Ni-Nx/Fe-Nx coordination environment promotes oxygen adsorption, charge redistribution, and rapid charge transfer, thereby enhancing the bifunctional oxygen electrocatalytic activity.