Unveiling the Axial Hydroxyl Ligand on FeN<sub>4</sub>C Electrocatalysts and Its Impact on the pH‐Dependent Oxygen Reduction Activities and Poisoning Kinetics
Xin Yang, Dongsheng Xia, Yongqiang Kang, Hongda Du, Feiyu Kang, Lin Gan, Jia Li
Abstract
Abstract FeNC materials have shown a promising nonprecious oxygen reduction reaction (ORR) electrocatalyst yet their active site structure remains elusive. Several previous works suggest the existence of a mysterious axial ligand on the Fe center, which, however, is still unclarified. In this study, the mysterious axial ligand is identified as a hydroxyl ligand on the Fe centers and selectively promotes the ORR activities depending on different FeN 4 C configurations, on which the adsorption free energy of the hydroxyl ligand also differs greatly. The selective formation of hydroxyl ligand on specific FeNC configurations can resolve contradictories between previous theoretical and experimental results regarding the ORR activities and associated active configurations of FeNC catalysts. It also explains the pH‐dependent ORR activities and, moreover, a previously unreported pH‐dependent poisoning kinetics of the FeNC catalysts.