Lignin-derived high-performance Fe-N-C nanotube catalysts for oxygen reduction and direct lignin fuel cells

Oxygen reduction reaction (ORR) catalysts derived from sustainable resources are desirable for fuel cell related electrochemical systems. Herein, a dual-valorization strategy of lignin is employed to construct an intertwined Fe-N-LCNT catalyst, and its performance is evaluated in direct lignin fuel cells (DLFCs). The CNT-assisted structure improves electrical conductivity and exposes abundant FeN active sites. Consequently, an onset potential (E_onset) of 0.93 V and a half-wave potential (E_1/2) of 0.87 V are obtained in 0.1 M KOH. Rotating ring-disk electrode (RRDE) measurements indicate a near four-electron ORR pathway (n ≈ 3.9) with <5% H₂O₂ yield. At 0.7 V, Fe-N-LCNT retains 61.4% of its initial current after 30 h, which is higher than that of Pt/C (52.06%). In addition, negligible activity loss is observed after the injection of 1.0 M methanol-demonstrating good methanol tolerance. When applied as the cathode in DLFCs, the catalyst delivers an open-circuit voltage of 0.68 V and a maximum power density of 0.11 mW·cm^-2. These results suggest that defect-engineered Fe-N-C structures derived from lignin can compete with Pt/C while offering a sustainable route for ORR electrocatalysis.