Effect of Active Site Poisoning on Iron−Nitrogen−Carbon Platinum-Group-Metal-Free Oxygen Reduction Reaction Catalysts Operating in Neutral Media: A Rotating Disk Electrode Study

Platinum-group-metal-free (PGM-free) catalysts are the most promising materials to substitute expensive platinum catalysts for efficient oxygen reduction reaction (ORR), particularly for microbial fuel cells. For these devices, contamination due to wastewater is one of the major issues, owing to the presence of various poisoning anions. The known nitrite contamination effect over PGM-free catalysts was studied by using the rotating disk electrode (RDE) technique in neutral media to understand its patterns. The results were then compared to other contaminants commonly found in wastewater such as chloride (Cl⁻), perchlorate (ClO₄⁻), and nitrate (NO₃⁻) in the concentration range of 0.05–50 mM. Onset potential (E_onset), half-wave potential (E_1/2), limiting disk current density (J_lim) and Tafel slope variations were the parameters exploited to identify specific or nonspecific adsorbed contaminants. Chloride and nitrate had no negative effect on ORR performance, whereas perchlorate slightly reduced the catalyst function with no permanent issues. Durability tests (1000 cycles) were also performed to ensure the stability of the catalyst for the relatively long time.