CO Poisoning Effects on FeNC and CNx ORR Catalysts: A Combined Experimental-Computational Study

CO poisoning as a probe for oxygen reduction reaction (ORR) active sites was examined on both iron nitrogen coordinated catalysts supported on carbon (FeNC) and nitrogen-doped carbon nanostructures (CNx). Rotating disk electrode (RDE) experiments show a partial decrease in the ORR activity of FeNC catalysts after CO exposure and no decrease for CNx catalysts. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy experiments after exposure to CO show a peak at 2033 cm(-1) (associated with linearly bound CO) on the FeNC catalysts and no peaks associated with adsorbed CO on the CNx catalyst surface. Density functional theory (DFT) calculations incorporating dispersion interactions of the adsorption energy of O-2 and CO were performed on a total of 16 proposed active sites for the FeNC and CNx catalysts. On CNx, all the sites show weak CO adsorption and only O-2 molecules are expected to adsorb, which matches the experimental observation of no poisoning. Several FeNC sites show CO binding energies similar in strength to that seen for Pt(111), but only two sites, namely FeN4/C pyridinic and FeN4/C pyrrolic, are found to bind CO stronger than O-2. DFT results suggest that the partial poisoning (instead of complete poisoning as found on Pt catalysts) observed in experiments is due to only some fraction of the active sites being blocked. DFT-derived CO stretch frequencies on FeNC show a similar redshift as observed in the DRIFTS experiments, which further confirms that the FeNC catalysts adsorb CO while the CNx catalysts only show weak physisorption.