Fe/N/C Nanotubes with Atomic Fe Sites: A Highly Active Cathode Catalyst for Alkaline Polymer Electrolyte Fuel Cells

Fe-containing N-doped carbons (Fe/N/C) are a promising Pt-alternative catalyst for the oxygen reduction reaction (ORR) and are believed to be more stable in alkaline media than in acids and thus particularly suitable to be applied as the cathode catalyst for alkaline polymer electrolyte fuel cells (APEFCs). However, there has hitherto been no successful report on high-performance APEFC based on the Fe/N/C cathode, the reason for which is still not quite clear. Here we report a high-performance Fe/N/C catalyst and its application in APEFC. The catalyst precursor is adenosine, an environmentally benign N-rich biomolecule, which is polymerized via a solvothermal process and then carbonized through pyrolysis. The resulting Fe/N/C nanotubes are thoroughly characterized by a variety of microscopy and spectroscopy (SEM, TEM, XRD, XPS, Raman, Mossbauer, and STEM-EELS), which reveal a high surface N/C ratio (8 at%) and atomic Fe sites well dispersed at the wall of the nanotubes. The catalytic sites are identified to be Fe-N-4. The volume-specific catalytic activity of the Fe/N/C catalyst toward the ORR is as good as that of the commercial 20 wt % Pt/C catalyst in alkaline solutions, and better in durability. The electronic conductivity of Fe/N/C turns out to be trivial in rotating-disk electrode experiments but key for fuel cell tests. The APEFC with Fe/N/C cathode (2 mg/cm(2) in catalyst loading) exhibits a peak power density greater than 450 mW/cm(2), the thus-far highest record in the literature for APEFC using a nonprecious metal cathode. Our findings not only deepen the understanding of the structure-activity relationship of the Fe/N/C catalyst but also mark a step toward its real application in APEFC.