Synergistic Oxygen Reduction Catalysis by Fe Nanoparticles and Atomic Fe-N_x Sites in MOF-Derived Carbon Nanotubes

The growing imperative to overcome energy conversion inefficiencies has spurred significant research into high-performance, economically viable, metal-carbon catalysts. This work presents a precisely engineered Fe@ZIF-8 precursor, where controlled encapsulation of Fe(acac)3 within the MOF pores yields Fe/FeNC-CNT upon pyrolysis. The resulting composite features carbon nanotubes (CNTs) that significantly improve electrical conductivity while forming a protective carbon matrix that mitigates Fe aggregation and leaching. It exhibits exceptional oxygen reduction reaction activity, with a reduction potential of 0.896 V and a large limiting current density of 5.23 mA cm-2, surpassing the performance of commercial Pt/C benchmarks. When implemented in zinc-air batteries, the Fe/FeNC-CNT catalyst achieves an open-circuit voltage of 1.551 V, a specific capacity of 783.57 mAh g-1, and a peak power density of 164.56 mW cm–2. In this case, the exceptional performance stems from the synergistic interplay between Fe nanoparticles and atomically dispersed Fe-Nx sites combined with the structural robustness imparted by the CNT framework. This unique combination of features positions Fe/FeNC-CNT as a promising, nonprecious metal alternative, effectively marrying the intrinsic advantages of CNTs with the catalytic benefits of both nanoscale and atomic iron species.