In this study, Vulcan XC72, which is a common carbon black support, is used, and its surface properties are controlled by heat treatments. Oxygen reduction reaction activity and durability were evaluated for platinum on surface controlled carbon, electrochemically. Additionally, we introduce our method to accelerate degradation of electrocatalysts using Environmental TEM (Hitachi HF-3300). For carbon oxidation, the air is introduced into the specimen chamber, and the specimen holder is heated up to 200 ^oC to accelerate degradation instead of cycling to high potential many times.

Regarding to the temperature of heat treatments, 1600 ^oC worked best in our studies. The surface of carbon black particles was graphitized, and a few graphitic layers were observed in TEM images. Oxygen reduction reaction activity was not much changed by the heat treatment, but the durability was significantly increased.

In order to understand the degradation mechanism on different carbon surface, the method using Environmental TEM was introduced. A new phenomenon of platinum particles embedded into Vulcan carbon with almost no agglomeration was observed. However, on graphitized Vulcan carbon surface, agglomeration more occurred, and embedding of platinum was rather suppressed. Since platinum on graphitized carbon showed much improved durability though the electrochemical analysis, embedding is believed to be a more predominate factor than agglomeration on degradation of PEFC performance.

Reference: X. Zhao, A. Hayashi, Z. Noda, K. Kimijima, I. Yagi, K. Sasaki, Electrochim. Acta 97 (2013) 33.