Ammonia Tolerance of Atomically Dispersed Single Metal Site Catalysts: Mechanistic Understanding and High‐Performance Oxygen Reduction Electrocatalysis

Abstract The anion‐exchange membrane direct ammonia fuel cell, as a carbon‐free fuel cell type, has recently received increasing attention albeit suffering from high cost of using the platinum‐group metal oxygen reduction reaction (ORR) catalysts. To pave the development of this promising power source, the atomically dispersed transition metal‐nitrogen‐carbon (M‐N‐C) materials with low cost and high ORR performance have allured to investigate their ammonia tolerance during the ORR. Herein, it is initially deconvoluted how compositional and structural elements of FeN₄ sites modulate catalyst's performance. Furthermore, ORR catalytic activities of the M‐N‐C (M = Fe, Co or Mn) and Pt/C catalysts are investigated in ammonia‐containing electrolytes, showing that M‐N‐C catalysts have better ammonia tolerance than Pt/C. Among others, the Fe‐N‐C exhibits the best ammonia tolerance with only 4 mV negative shifts of half‐wave potential, 2.7% decrease of current, and negligibly irreversible activity loss. The superior ammonia tolerance of MN₄ sites to Pt (111) surface is further confirmed by density functional theory calculations. The adsorption capacity of MN₄ for O₂ is higher than NH₃ and the bonding force between MN₄ and O₂ is stronger than NH₃, whereas opposite adsorption capacity and bonding force trends are observed on Pt (111) surface.