Fundamental Insights in Degradation Mechanisms of Pt/C Nanoparticles for the ORR

Despite large efforts to develop and optimize PEM fuel cell electrodes for commercialization, degradation processes on the widely used Pt/C catalyst materials are not fully understood to date. In this work, we analyzed the changes of morphology and structure of commercially available Pt/C catalysts by applying different electrochemical accelerated degradation protocols using a rotating disk electrode (RDE) technique. The Pt nanoparticles (Pt NP) as well as carbon support material were characterized by using ex situ transmission electron microscopy (TEM) and Raman spectroscopy. We point out that the growth of the Pt NP and the oxidation of the carbon support material are strongly influenced by the applied potential range. In particular, the "start/stop" experiments (2,000 potential cycles, 0.5 - 1.5V vs. RHE) show the highest loss in ECSA and strongest growth of Pt nanoparticles compared to the "carbon corrosion" (2,000 cycles, 1.0 - 1.5V vs. RHE) and "lifetime" (10,000 cycles, 0.5 - 1.5V vs. RHE) protocols. In addition, the Raman spectra of the treated Pt/C indicate that the electrochemical oxidation of defect-rich carbon sites is accelerated by applying higher anodic potentials (above 1.0V vs. RHE) and in the presence of smaller Pt NP. Altogether, our results provide a deeper understanding in the development of more stable and highly active PEM fuel cell catalysts.