In situ growth of B, N-doped Fe₃C-encapsulated carbon nanotubes on wood-derived carbon for high-performance Zn-air battery electrocatalysts 

The use of wood-derived porous carbon as an electrocatalyst in metal-air batteries has received significant attention. Although significant efforts have focused on developing and optimizing active sites, the insufficient electrical conductivity of wood-derived carbon as a catalytic electrode is often overlooked. This study presents the in situ growth of heteroatom-doped carbon nanotubes (CNTs) encapsulating Fe₃C nanoparticles (Fe₃C@BNC) within wood-derived carbon. Iron carbide possesses an electronic configuration similar to that of noble metals and exhibits high catalytic activity. The addition of CNTs enhances the conductivity of the wood-derived carbon, achieving a cross-sectional conductivity of 97.2 S m⁻¹ and enabling efficient electron transport during electrochemical reactions. Boron and nitrogen co-doping modifies the electronic structure of CNTs, further accelerating electrocatalytic reactions. The resulting Fe₃C@BNC exhibits excellent catalytic activity for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Particularly, Fe₃C@BNC features a half-wave potential (E_1/2 = 830 mV) for ORR and a low overpotential of 250 mV at 10 mA cm⁻² for OER. The narrow potential gap of 650 mV between ORR and OER significantly exceeds that of commercial Pt/C+RuO₂ catalysts. Upon use as the air cathode in Zn-air batteries, Fe₃C@BNC achieves a specific capacity of 804.5 mA h g⁻¹ and exhibits excellent cycling stability, maintaining performance for up to 420 h. This study provides valuable insights into the design of carbon-based bifunctional oxygen electrocatalysts and highlights the high-value utilization of forest biomass-derived materials in renewable electrochemical energy conversion devices.