Experiments

A 250W portable fuel cell (hereafter referred to as the power source) was used for the experiments. 30 cells with 190 cm 2 of active electrode area were used in the stack. The supply and removal of water from inside the stack can be calculated by measuring the amount flow, temperature and humidity of the reactive gas supplied to the stack and the exhaust from the stack. However, when weight changes in the stack are measured from when this power source is being stored until it is started up, operated and stopped, it is thought that the amount and rate of water accumulated in the stack and the amount and rate of exhaust from the stack can be calculated with greater ease and more accuracy. Figure 1 shows the method used in the experiment The power source was placed on an electronic balance. Weight data and power source operation data were sent to and recorded in a computer. Fuel hydrogen was supplied to the stack through a tube from a hydrogen gas cylinder. The concentration and volume of the phosphoric acid were calculated in the following manner.

(1) The amount of the phosphoric acid when the stack was assembled was used for the amount in the stack.

(2) The temperature and humidity of the atmosphere around the stack was measured immediately before it was started up, and the initial phosphoric acid concentration value was calculated from the relationship[3]between the steam pressure and concentration of the phosphoric acid water solution.

(3) It was assumed that all weight changes were the result of the phosphoric acid absorbing and releasing the water.

(4) It was assumed that only the phosphoric acid within the active electrode area absorbed and released water.

(5) It was assumed that concentration of the phosphoric acid in each component of the electrode was uniform.

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