Carbon Nanotube-Encased FeNi Alloy/N-Doped Carbon ORR Catalyst: High Efficiency and Stability

Abstract

The efficient reduction of oxygen in fuel cell technology using platinum group metals (PGMs) faces challenges like sluggish kinetics, high costs, and poor durability. To overcome these limitations, PGM-free oxygen reduction reaction (ORR) electrocatalysts are sought after. Transition-metal-based electrocatalysts, specifically metal-nitrogen co-doped carbon (M-N/C, M = Fe, Co, etc.), have emerged as promising alternatives due to their abundant pore structures, high surface area, conductivity, and cost-effectiveness. This review explores various non-precious metal electrocatalysts for ORR, highlighting pyrolyzed transition metal nitrogen-containing complexes on carbon (M–Nx/C) as outstanding candidates, with Fe-N/C demonstrating remarkable performance. In this study, we introduce a novel approach to construct Fe-Nx doped large-diameter carbon nanotubes (Fe,Ni-N/C) by pyrolyzing zeolitic imidazolium frameworks-8 (ZIF-8) functionalized with nickel acetate. This approach capitalizes on strong intercalation between acetate and metal ions, promoting Fe-Nx active site formation while generating large-diameter carbon nanotubes. The resulting catalyst facilitates rapid mass transport and maximizes active site exposure, nearing the performance of Pt/C. Our catalyst exhibits an initial potential of 1.03 V, a half-wave potential of 0.88 V, and a limit current of 5.5 mA cm−2. Remarkably, it retains 85.7% of its initial performance in a 36,000 s chronoamperometry test, demonstrating superior durability and methanol toxicity resistance compared to Pt/C. Large-diameter carbon nanotubes offer a potential alternative electrocatalyst, eliminating the need for templates, simplifying mass production for applications like sensors, supercapacitors, and lithium-ion batteries. Furthermore, our Fe,Ni-N/C catalyst outperforms commercial Pt/C, making it a promising choice for ORR applications in fuel cells.