Type of presentation: Poster

ID-12-P-1550 In situ TEM/EELS study of structural changes of Pt/GC electrocatalyst in CO gas

Yaguchi T.1, Shimizu T.2, Kamino T.2, 3
1Hitachi High-Technologies Corp., Ibaraki, Japan, 2Japan Automobile Research Institute, Ibaraki, Japan, 3University of Yamanashi, Yamanashi, Japan
yaguchi-toshie@naka.hitachi-hitec.com

 Improving the long-term performance of catalyst is one of the most important issues in polymer electrolyte fuel cell (PEFC) technology. Environmental transmission electron microscopy (ETEM) has proven to be an effective characterization tool for understanding the degradation mechanism of the catalytic materials. Our goal is to optimize the instrumentation which can simulate the working environment of a catalyst inside the microscope. For this purpose, we have developed an ETEM based on a conventional analytical TEM and a specimen heating holder equipped with a gas injection nozzle 1). Different from conventional ETEM techniques, the specimen heating holder is designed to introduce a gas locally to the specimen. The inner diameter of the gas nozzle is 0.5 mm, and the distance between the nozzle and the specimen mounted on a heating element is 1.0 mm. This unique design of the holder allows a gas pressure up to 100 Pa near the specimen, while maintains a vacuum of 10-5 Pa in the electron gun chamber. In order to study the effect of gas on the structural changes during heating, it is important to be able to switch gas quickly. In our design, gas bottles are directly connected to the specimen heating holder with a path length of 20 cm, which is much shorter than that of conventional ETEM. Thus, we can switch a gas in several seconds as it has been verified by electron energy-loss spectroscopy (EELS) gas analysis. The advantage of the quick gas switch benefits our in situ TEM study of energy-related nanomaterials.
 In this paper, we report an in situ TEM/EELS study of the degradation mechanism of a Pt/graphitized carbon (GC) electrocatalyst, using a Hitachi H-9500 ETEM equipped with a Gatan GIF EELS which has an energy resolution of 1.0 eV at 300 kV. The gas pressure was maintained at 60 Pa near the specimen which has been heated up to 200 oC. Fig. 1 presents the EELS analysis of the CO gas, showing the characteristic sharp π* peak of C-K and high signal-noise ratio. Fig. 2 shows the EELS spectrum of a carbon support of Pt/GC catalyst heated to 100 oC in 60 Pa of CO gas atmosphere. A series of TEM images obtained during the in situ dynamic TEM observation are shown in Fig. 3. Nucleation and growth of Pt particles occurred when the CO gas pressure was increased to 60 Pa. Other structural changes such as formation of PtO2 were characterized by high-resolution TEM and selected nano area electron diffraction analysis. The results from the improved ETEM demonstrated the applicability of this technique for the evaluation of the state of the graphitized carbon black-supported Pt catalysts.
1) Kamino T, et al, J. Electron Microsc.54, (2005) pp.497–503.

Fig. 1: EELS spectrum of the CO gas at 60 Pa: the characteristic sharp π* peak of C-K and high signal-noise ratio.

Fig. 2: EELS spectrum of the carbon support of the Pt/GC catalyst heated to 100 oC in 60 Pa of CO. It shows the convolution of π* peak from CO gas and ρ* peak from solid carbon support.

Fig. 3: Sequential TEM images recorded during in situ dynamic ETEM study. Nucleation and growth of Pa particles occurred when the CO gas pressure increased to 60 Pa.