Roles of Carbon Corrosion and Ligation in Fe–N–C Electrocatalysts and Their Implications for Sabatier Behavior
Sirui Li, Piotr Zelenay, Wilton J. M. Kort-Kamp, Edward F. Holby
Abstract
Atomically dispersed Fe–N–C electrocatalysts are a promising alternative to platinum group metals for the oxygen reduction reaction (ORR) in energy conversion technologies. However, their widespread adoption is limited by their durability during operation. While substantial efforts have focused on improving ORR activity, the degradation mechanisms affecting Fe–N–C catalysts remain underexplored. Strategies to co-optimize activity and durability are needed but should be based on a mechanistic understanding. To address this, we apply density functional theory (DFT) to investigate the impact of carbon corrosion on the ORR activity and stability in model Fe–N–C structures. We reveal that carbon (C) corrosion detrimentally impacts Fe–N–C catalyst performance in pristine structures, resulting in a lower calculated ORR limiting potential (lower activity) and a lowered Fe dissolution potential (lower resistance to metal dissolution). However, the addition of an ORR intermediate species as an axial ligand in certain C-corroded structures can restore and even enhance activity. This interplay is best understood through the general finding that C corrosion leads to stronger binding between Fe–N–C and ORR intermediates, and ligation leads to weaker binding. By explicitly considering the chemical binding of oxygen in our reaction pathway, we also redefine scaling relations within these systems. Importantly, we find that both the bound *OO state and *OOH state scale with the free energy *OH binding with only a minor difference in slope, leading to a relatively flat “under-binding” side of the Sabatier “volcano” plot, making it perhaps more appropriately called a Sabatier “mesa” in such cases.