A pore-confined strategy for synthesizing CoFe nanoparticles in mesoporous biocarbon matrix as advanced bifunctional oxygen electrocatalyst for zinc–air battery

Designing rational transition-metal/carbon composites with highly dispersed and firmly anchored nanoparticles (NPs) to prevent agglomeration and shedding is crucial for realizing excellent electrocatalytic performances. Herein, a biomass pore-confined strategy based on mesoporous willow catkin is explored to obtain uniformly dispersed CoFe NPs in N-doped carbon nanotubes and hollow carbon fibers (CoFe@N-CNTs/HCFs). The resultant catalyst exhibits enhanced electrocatalytic performance, which affords a half-wave potential of 0.86 V (vs. RHE) with a limited current density of 6.0 mA·cm⁻² for oxygen reduction reaction and potential of 1.67 V (vs. RHE) at 10 mA·cm⁻² in 0.1 M KOH for oxygen evolution reaction. When applied to rechargeable zinc–air batteries, a maximum power density of 340 mW·cm⁻² and long-term cyclic durability over 800 h are achieved. Such superior bifunctional electrocatalytic activities are ascribed to the biocarbon matrix with abundant mesopores and unobstructed hollow channels, CoFe NPs with high dispersion and controllable nanoscale and the hybrid composite with optimized electronic structure. This work presents an effective approach for constraining the size and dispersion of NPs in a low-cost biocarbon substrate, offering valuable insights for designing advanced oxygen electrocatalysts.