Durability of Pt3Co/C Cathodes in a 16 Cells PEMFC Stack: Degradation Mechanisms and Modification of the ORR Electrocatalytic Activity

Abstract

In this work, we operated a 16-cells stack based on Pt/C anode and Pt3Co/C cathode under H2/air at constant current (j = 0.6 A cm-2) for 1124 h. The MEA were characterized with special emphasis on the cathode electrocatalyst, using physical, chemical and electrochemical techniques after different life stages: as received (fresh: 0 h), conditioned (17 h) and aged for 504 or 1124 h. The fresh Pt3Co/C cathode catalyst is not stable during PEMFC operation and suffers compositional changes. In particular, the dissolution of Co atoms at the surface yields to the formation of a Pt-shell/Pt-Co alloy core structure. The high electrochemical potential of the cathode induces formation of surface oxides and drives continuous Co surface segregation. The dissolution of Co atoms at the surface increases the affinity of the surface to oxygenated and hydrogenated species and renders it less active towards the ORR.