Nitrogen-rich Fe-N-C materials derived from polyacrylonitrile as highly active and durable catalysts for the oxygen reduction reaction in both acidic and alkaline electrolytes

Fe-N-C catalyst with a core-graphitic shell nanostructure was synthesized by pyrolysis of polyacrylonitrile (PAN)-coated carbon black in the presence of iron salts. The attained catalyst exhibits high performance towards the oxygen reduction reaction (ORR) in both acid and alkaline electrolytes, with the half-wave potentials of 97 my negative and 39 mV positive to Pt/C in 0.5 M H2SO4 and 0.1 M NaOH, respectively. Meanwhile, the catalyst shows high stability and remarkable tolerance towards methanol. The XRD analysis demonstrates that both the introduction of iron and an increase of the pyrolysis temperature promote the growth of layers in the graphitic shell. With the rise of pyrolysis temperature, increases of the catalytic activity and Fe3+ reduction potential are observed, as well as the relative content of nitrogen of Fe-N. type and N 1s binding energy. Moreover, a linear relationship between the logarithm of ORR turnover number and the Fe3+ reduction potential is observed. Based on these findings, the enhanced ORR performance of the catalyst can be attributed to the growth of pi -conjugated graphitic layers, which modulates the electronic structure of embedded Fe-N-4 sites. In addition, the presence of an accessible core-graphitic shell nanostructure facilitates the mass transport of ORR-relevant species between the electrolyte and the catalytic sites. (C) 2017 Elsevier Inc. All rights reserved.