Synergistic effects of hierarchical porous structures and ultra-high pyridine nitrogen doping enhance the oxygen reduction reaction electrocatalytic performance of metal-free laminated lignin-based carbon.

Construction of non-metallic biomass-carbon based catalysts for fuel cell air cathode applications has attracted great attention in recent years. In this work, a convenient and clean technique was developed to fabrication nitrogen-doped lignin-based hierarchical porous lamellar carbon (N-LHPC) via lignin as the carbon precursor, melamine/urea as the nitrogen source and ZnC2O4.2H2O as the chemical activator. The N-LHPC has a high specific surface area (491.5 m2 g-1) and macroporous/mesoporous/microporous structures. The nitrogen doping of N-LHPC can reach 16.37 wt%, with a high pyridinic nitrogen content of 41.39 at.%. N-LHPC exhibits a high half-wave potential (0.87 V) and a large limiting current density (5.75 mA cm-2) in 0.1 mol KOH media which is comparable to the commercial Pt/C catalysts. Furthermore, N-LHPC was assembled as air cathode catalyst for Zn-air batteries to evaluate its practical catalytic performance, and the power density was as high as 191 mW cm-2, which was superior to the 20 wt% Pt/C electrocatalyst. This research demonstrates that lignin is a promising carbon source for the fabrication of high catalytic activity and economical electrocatalysts for energy storage systems.