Takahiro Shimizu

The purpose of this research is to increase the processing efficiency by performing ELID grinding using fixed abrasive grains for brittle material of high hardness such as sapphire. Grinding of sapphire involves problems of falling off and burying of abrasive grains. As a solution, use a high hardness iron plating diamond wheel made by electroplating method. Moreover, in order to obtain good surface roughness for sapphire, it is considered effective to increase the processing pressure applied to the abrasive grains. Therefore, we developed a grinding stone with the hardness is set at a Vickers hardness value of 600. This grinding wheel and sapphire were attached to a triaxial processing machine, and ELID grinding processing was performed on the A side of sapphire by a traverse method. As a result of experiments, it was confirmed that the developed grinding wheel has removal ability against sapphire. In addition, good surface roughness could be confirmed at more places than the processing result of Vickers hardness value of 400.

Polymer electrolyte fuel cells hold great potential for stationary and mobile applications due to high power density and low operating temperature. However, the structural changes during electrochemical reactions are not well understood. In this article, we detail the development of the sample holder equipped with gas injectors and electric conductors and its application to a membrane electrode assembly of a polymer electrolyte fuel cell. Hydrogen and oxygen gases were simultaneously sprayed on the surfaces of the anode and cathode catalysts of the membrane electrode assembly sample, respectively, and observation of the structural changes in the catalysts were simultaneously carried out along with measurement of the generated voltages.

In situ TEM observation of the Pt/C electrocatalyst was conducted to analyze the structural change of Pt nano particles and carbon support under the pseudo cathode environment. The Pt nano particles were observed to move actively on the support in humidified air, while the particles to remain at their original position on the support in dry air. The in situ high-resolution TEM revealed that the driving force behind the active movement of Pt particles was the oxidation of carbon support selectively at the interface between Pt particle and carbon support, accelerated by water. It appears that the humidity of the air plays an important role in the degradation of the Pt/C electrocatalyst.

Potential cycle tests that simulate the operation of a fuel cell vehicle are widely adopted as a durability testing method of membrane-electrode assemblies (MEAs). The Fuel Cell Commercialization Conference of Japan (FCCJ) has proposed methodologies for testing MEAs and their materials in 2007, focusing on the evaluation of the durability of electrode materials. The two protocols, start/stop durability test and load cycle durability test, were revised in 2011 based on the up-to-date knowledge concerning fuel cell durability. In this study, we applied the revised protocols to a standard electrocatalyst, and the effect of the revision was verified. We have demonstrated that the revision of the protocols accelerates the evaluation of fuel cell materials and verified that the revised protocols effectively separate the degradation of Pt electrocatalyst from that of carbon support.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

To clarify the influence of moisture on the structural changes of heated nano materials, in situ high temperature transmission electron microscopy (TEM) has been carried out using a conventional analytical TEM combined with a gas injection-specimen heating holder. Air with high moisture content, above 94% relative humidity (RH), from a humidifier was directly injected onto the heated platinum catalyst dispersed on carbon black (Pt/CB), and the morphological changes of the specimens were observed at high magnification dynamically. The result of the experiment was compared with a result obtained from an experiment using air with a low moisture content, 34% RH. Active movement of the Pt particles, leading agglomeration and grain growth, occurred prior to degradation of the CB support at high moisture content. In contrast, the degradation of the CB support leading agglomeration and grain growth of the Pt particles occurred before the displacement of the Pt particles on the CB supports in a low humidity environment.