Preparation of Fe/N Double Doped Carbon Nanotubes from Lignin in Pennisetum as Oxygen Reduction Reaction Electrocatalysts for Zinc–Air Batteries

Obtaining high value-added products from renewable lignocellulosic biomass is very attractive but still a major challenge. The underutilization of lignin for a high value is considered one of the main obstacles. Herein, we report Fe/N double doped carbon nanotubes with a hollow structure prepared by pyrolysis of an Fe–lignin complex and dicyandiamide. Fe/N double doped carbon nanotubes are expected to replace Pt-based catalysts as efficient, low-cost, and sustainable non-precious metal electrocatalysts for the oxygen reduction reaction in zinc–air batteries. The Fe/N double doped carbon nanotubes as catalysts exhibited good ORR activity with a half-wave potential and onset potential of 0.846 and 0.972 V, respectively, which is comparable to the ORR performance of the state-of-the-art 20% Pt/C catalyst, and the catalyst also has good stability. The primary zinc–air batteries of this catalyst exhibit a high open-circuit voltage, and its good stability ensures that the zinc–air batteries assembled with this catalyst can still maintain high performance during long-term discharge. The enzymatic effect of the cellulosic material obtained by pretreatment in this work is substantially enhanced, and the use of the isolated lignin for the preparation of polyatomically doped catalysts and for zinc–air batteries makes this work demonstrate an integrated biorefinery strategy. This work provides a low-cost and high-efficiency route for the preparation of polyatomically doped carbon nanotubes from lignin, which provides a good direction for the high value-added utilization of lignin.