Experimental and DFT Investigation into Chloride Poisoning Effects on Nitrogen-Coordinated Iron-Carbon (FeNC) Catalysts for Oxygen Reduction Reaction

Iron-nitrogen-coordinated carbon-supported (FeNC) catalysts have been explored for application as oxygen depolarized cathode (ODC) catalysts that perform oxygen reduction reaction (ORR) in electrochemical chlorine production systems. One important requirement for ODC catalysts is the resistance to poisoning of their ORR active sites in the presence of chloride anions. This work combines the use of experimental and computational methods to study the effect of exposure of the FeNC catalyst to chloride anions. Electrochemical measurements indicate partially reversible poisoning of the FeNC catalyst in the presence of chloride anions under ORR conditions. Calculations performed using density functional theory on various FeNxCy site models are used to study competitive adsorption between the Cl anions and O-2 via both direct nonelectrochemical adsorption of O-2 and via a proton-electron transfer step to form OOH* through the ORR associative mechanism. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy measurements together with density functional theory predictions of binding energies and Bader charges indicate a poisoning effect caused by adsorption of CI anions on the Fe-centered active sites of FeNC catalysts. The results presented in this work also help explain the partial poisoning effect in FeNC catalysts, wherein certain FeNxCy sites are poisoned by Cl-, while others are not. For some sites, the Cl- poisoning effect is found to be reversed when the applied potential reaches similar to 0 V versus the reference hydrogen electrode.