Development of Model Gas Diffusion Electrode Apparatus for the Performance Evaluation of Fuel Cells

Currently, fuel cells are of great interest in research and development as a highly efficient power generating apparatus free of toxic emissions. For example, phosphoric acid fuel are now on the commercial stage for industrial use, and the practical use for solid polymer electrolyte fuel cells is on the way to be in the market in the form of electric vehicle and household electric supplies by early 21^st century.

As key technology for the development of fuel cells, the research onthe optimization of the gas diffusion electrode, which is the core of fuel cells, to realize its highly efficient performance is being carried out actively. Gas diffusion electrode are important components in which fuel gas (hydrogen, etc.) or oxidation gas (oxygen or water) are converted to products(H^�{ion or water, etc.) by emitting and receiving electrons. There are still many research themes that should be investigated and developed in order to attain highly efficient performance gas diffusion electrodes; and the research on the development of a new electrode catalyst (substances to promote reactions) as well as a new fabrication method of electrodes are few among others. Relying more or less on the experimental parameters in the try-and-error screening of the performance of catalysts is the actual situation.

Historically, when the above investigation is carried out, experimental apparatus of fuel cells (real cells or single unit electrochemical half cells) have been used for power generating investigations to evaluate the performance in general.

However, constructing fuel cells for this purpose requires much time and cost. In addition, the complexity of analyses involving a variety of experimental parameters is enormous so that it has been difficult to extract and analyse the factors which need to be focused and examined under specific conditions.

Therefore, the development of the apparatus which enables a simple and reproducible investigation about the performance and durability of gas diffusion electrodes has long been expected.

The following figure 1 is the apparatus specially developed for the purpose mentioned above. This is a new model system for the evaluation of catalysts in the gas diffusion electrodes, and this apparatus has been investigated whether it could reproduce the performance in the real fuel cell conditions.

In this apparatus, a test specimen of catalyst loaded on carbon paper is mounted in a Teflon holder and half-dipped in test solutions. The specimen is designed to revolve in the air and solution phase with specific speed, thereby experiencing alternative contacts with gas/liquid phases. The supply of oxygen gas is found to be the largest at the meniscus of the gas/liquid interface with the sample electrode.

The apparatus has been observed to successfully simulate the gas diffusion electrodes, especially those of the polymer electrolyte fuel cells. The performance evaluation of highly dispersed catalysts and mixed catalysts resembles those of the results by electrochemical measurements using rotating ring disk electrodes and a single fuel cell test stand.(Figure 2)

This apparatus is developed by National Institute of Materials and Chemical Research in collaboration with Science University of Tokyo and Mitsubishi Electric Corporation in order to carry out the material investigations of electrode catalysis for fuel cells as well as gas diffusion electrodes. The manufacturer of the apparatus is Hokuto Denko Ltd.

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(Figure 1 The apparatus seen from outside)
Half-Immersed Rotating Vertical Electrode (HIRVE) with rotation and temperature control units

Figure 2