A comparison of N-containing carbon nanostructures (CNx) and N-coordinated iron–carbon catalysts (FeNC) for the oxygen reduction reaction in acidic media

Abstract

In light of the debate about the role of the transition metal in non-precious metal catalysts (NPMCs), two different NPMCs, CNx and FeNC, were compared for activity toward oxygen reduction in acidic media and characterized using various techniques, including X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), superconducting quantum interference device (SQUID) magnetometry, inductive-couple plasma optical emission spectrometry (ICP-OES), and temperature-programmed oxidation (TPO). The effect of acid-washing as well as long-term exposure to fuel cell and half-cell environment on both catalysts was also studied. Although FeNC exhibited a much higher initial activity than CNx, it was seen to degrade rapidly in both half-cell and fuel cell environments, while CNx retained much of its initial activity. The results discussed are sought to clarify some of the ambiguity in the role of the transition metal in these two catalysts and help establish that they are indeed two different materials with different active sites that catalyze ORR.