Durability of Pt_3Co/C Cathodes in a 16 Cells PEMFC Stack: Degradation Mechanisms and Modification of the ORR Electrocatalytic Activity

摘要

The oxygen reduction reaction (ORR), which is the cathodic reaction in a proton-exchange membrane fuel cell (PEMFC) and in several other important processes for energy conversion, is a widely studied reaction. From the catalytic point of view, Pt is the best electrocatalyst and its activity can be increased upon alloying with a 3d-transition metal M such as Cr, Co or Ni (1-9). Recently, Stamenkovic et al.(10) showed that the near-surface composition of bulk Pt_3M alloys can be tailored at the atomic scale by appropriate thermal or electrochemical procedures to form a "sandwich-segregation" /"Pt-skin" or a "Pt-skeleton" structure, respectively. Interestingly, those surfaces perform better than the mother alloy for the ORR, this statement being also verified for nm-sized materials (11-13). On the other hand, high catalytic activity is meaningless if the bimetallic surface is unstable upon operation. Based on electrochemical and physical measurements, it has been shown that both "Pt-skin" and "Pt-skeleton" surfaces are stable in liquid electrolyte (4, 5, 10, 13, 14) but, so far, their durability remains unexplored during long-term PEMFC testing (15).