Disagreement on the Degradation Mechanism and Applicability of Kinetic Models for Non-Platinum Group Metal Catalysts in Polymer Electrolyte Membrane Fuel Cells

One large roadblock to the development of commercially viable hydrogen fuel cells is the cost of the platinum group metal (PGM) oxygen reduction reaction (ORR) catalysts used in proton-exchange membrane fuel cells (PEMFCs). Unfortunately, similarly active catalysts, like Fe-N-C catalysts, have suffered from stability issues limiting their use. To better understand these stability issues and design better catalysts a number of degradation mechanisms have been proposed and experimentally tested including demetalation, autocatalysis, and more. Recently, the paper of Zhang et al proposed a model with an initial fast exponential decay due to demetalation of active sites in micropores followed by a second, slower demetalation of active sites in mesopores for FeN_x containing catalysts.¹ They found this to better fit polarization curves for the catalyst decay for FeN_x catalysts while the Los Alamos² autocatalytic model reproduced data for non Fe containing catalysts and fluorine poisoned Fe catalysts. The work of Zhang et al, the comment of Yin et al³ (Los Alamos), and the response of the original authors⁴ is discussed.

Bibliography



(1) Zhang, G.; Yang, X.; Dubois, M.; Herraiz, M.; Chenitz, R.; Lefèvre, M.; Cherif, M.; Vidal, F.; Glibin, V. P.; Sun, S.; Dodelet, J.-P. Non-PGM Electrocatalysts for PEM Fuel Cells: Effect of Fluorination on the Activity and Stability of a Highly Active NC_Ar + NH3 Catalyst. Energy & Environmental Science 2019, 12 (10), 3015–3037. https://doi.org/10.1039/c9ee00867e.



(2) Yin, X.; Zelenay, P. (Invited)Kinetic Models for the Degradation Mechanisms of PGM-Free ORR Catalysts. ECS Transactions 2018, 85 (13), 1239–1250. https://doi.org/10.1149/08513.1239ecst.



(3) Yin, X.; Holby, E. F.; Zelenay, P. Comment on “Non-PGM Electrocatalysts for PEM Fuel Cells: Effect of Fluorination on the Activity and Stability of a Highly Active NC_Ar + NH3 Catalyst” by Gaixia Zhang, Xiaohua Yang, Marc Dubois, Michael Herraiz, Régis Chenitz, Michel Lefèvre, Mohamed Cherif, François Vidal, Vassili P. Glibin, Shuhui Sun and Jean-Pol Dodelet, Energy Environ. Sci., 2019, 12, 3015–3037, 10.1039/C9EE00867E. Energy & Environmental Science 2021, 14 (2). https://doi.org/10.1039/d0ee02069a.

(4) Dodelet, J.-P.; Glibin, V.; Zhang, G.; Kramm, U. I.; Chenitz, R.; Vidal, F.; Sun, S.; Dubois, M. Reply to the “Comment on ‘Non-PGM Electrocatalysts for PEM Fuel Cells: Effect of Fluorination on the Activity and Stability of a Highly Active NC_Ar + NH3 Catalyst’” by Xi Yin, Edward F. Holby and Piotr Zelenay, Energy Environ. Sci., 10.1039/D0EE02069A. Energy & Environmental Science 2021, 14 (2). https://doi.org/10.1039/d0ee03431b.