Acid Distribution In Phosphoric Acid Fuel Cells

I. Okae, A. Seya, M. Umemoto Fuji Electric Co.,Ltd 7 YawataKaigan-dori Ichihara-shi Chiba 290, Japan

Introduction

Electrolyte acid distribution among each component of a cell is determined by capillary force when the cell is not in operation, but the distribution under the current load conditions had not been clear so far.

Since the loss of electrolyte acid during operation is inevitable, it is necessary to store enough amount of acid in every celL But it must be under the level of which the acid disturbs the difiusion of reactive gases. Accordingly to know the actual acid distribution during operation in a cell is very important

In this report, we carried out experiments to clarify the distribution using small single cells.

A phenomenon of acid transfer

To estimate the acid distribution among components of a cell, the acid fill level (AFL) of each of them was measured. The AFL is defined as the ratio of the volume of absorbed acid to the total pore volume of each component.

When the AFL is measured after cell operation in general, the measured values represent the acid distribution determined almost by capillary forces of each component. It is not necessarily the distribution during operation, because it takes many minutes or some hours to disassemble the cell into each parts. And no descriptions concerning the time of disassembly can be seen in the papers which deal with the acid distribution in a cell [ e.g. 1 ]. Therefore we used a special holder and simple structure cells which could be disassembled into each component within extremely short time, thus measured the acid distribution of the load conditions.

Figure 1 shows the single cell used in this study. Each catalytic layer of cathode and anode (A-Cat & F-Cat) was supported by porous carbon substrate (A-Sub & F-Sub). Effective area of each electrode was 3cm2, and the ribbed plates (A-RP & F-RP) made of porous carbon were set for reactive gases at upper and lower of each electrode. The weight of every component was measured in advance. In this experiment, the acid _ I

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