Electrochemical evaluation of the degradation behavior of Pt/C cathode catalyst using porous microelectrode

Abstract

In order to better understand the cathode catalyst degradation of a polymer electrolyte membrane fuel cell, electrochemical measurements of oxygen reduction reaction (ORR) at a 47 wt% platinum-loaded carbon (Pt/C) have been conducted using porous microelectrode techniques before and after the polarization for 15 hours. This technique enables an evaluation of the ORR at the Pt/C powder electrocatalyst without any use of binder materials such as Nafion. In the ORR polarization curve at the Pt/C-containing microelectrode, a limiting current is clearly observed in the oxygen saturated 0.5 mol dm -3 sulfuric acid. The Tafel plot analysis revealed only a 60 mV/decade slope. After a 15-hour polarization of the Pt/C at +0.7, +0.8, and +0.9 V vs. RHE in an oxygen atmosphere, the following electrochemical measurement demonstrated that (i) the ORR i-E curve completely shifted in the cathodic direction by about 10 mV, (ii) the electrochemical surface area measured in a nitrogen atmosphere by cyclic voltammography decreased to 90-94 %, and (iii) the limiting current density decreased to 85-81 % at 0.7 V vs. RHE.