Quantifying and Understanding PGM-Free Oxygen Reduction Reaction Active Sites by in Situ Molecular Probes

Abstract

Gaining a better understanding of PGM-free oxygen reduction reaction (ORR) catalyst active site structure and activity relationships is key to developing more active catalysts. Active sites in a variety of Fe-N-C catalysts including commercial Pajarito Powder catalyst, with a range of activity and durability, were studied via in situ catalyst poisoning using thiol-molecular probes. The selectivity and extent of catalyst de-activation by the probes was monitored by comparing changes in ORR activity of the catalysts and N-containing carbon materials. Electrochemical stripping of the molecular probe was used to calculate the concentration of available active sites. These experiments were coupled with catalyst degradation and Fe-leaching experiments to better understand the specificity of the molecular probe binding. Probe-treated and untreated catalysts were also characterized using XPS. We plan to use these methods to better understand structural factors of the Fe-N-C active site, as well as the surrounding NC structure that may influence catalyst activity or durability.This work was supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) through Electrocatalysis Consortium (ElectroCat).