Experiments

To investigate the PTFE effect in the electrode, FIFE content was varied in the range of from 25 to 65 weight percent at the sintering temperature of 350 "C. To investigate the sintering temperature effect in the electrode, temperature was varied in the range of from 310 to 390 "C and PTFE content was 45 weight percent.

Phosphoric Acid absorption on electrocatalyst layer and the cathode polarization are measured in 190 "C phosphoric acid. When the temperature of electrolyte is heated from room temperature to WOt;, the acceleration time is defined as the 0 hour. The 24 hour acceleration test is defined as the condition when the electrode is placed in open circuit potential for 24 hours under 190*0.

RESULTS AND DISCUSSION'

Acid absorption in electrocatalyst layer with PTFE contents is shown in Fig.l. Acid absorption in electrocatalyst layer is increased with increasing time and saturated after 10 hours. Acid absorption in electrocatalyst layer is increased rapidly in the case of low PTFE contents like 25 wt%. In the case of high PTFE contents like 65 wt.%, the slow rate of acid saturation in electrocatalyst layer-is observed. But both eases are saturatcd-within 10 hours.

In phosphoric acid fuel cell, carbon corrosion in clectrocatalyst layer and the loss of FIFE film are produced continuously with increasing operation hours. The loss of PTFE film leads to decrement of hydrophobicity in electrocatalyst layer, phosphoric acid can be penetrated continuously into electrocatalyst layer. When the electrocatalyst contacts with phosphoric acid electrolyte, carbon corrosion and loss of PTFE film start in electrocatalyst layer. The corrosion of carbon is more severe when the electrocatalyst layer is placed at OCP. During acid absorption test acid absoiplion rate decreases with increasing acid absorption time.After acid absorption arrived at saturation, the increased weight of electrocatalyst layer by acid absorption is same as its weight loss by carbon corrosion and loss of PTFE loss. Therefore the acid absorption is apparently shown to be saturated.

Electrode performance as a function of PTFE contents is shown in Fig.2. With increasing PTFE contents, the performance of cathode increases in the low PTFE region but decreases in the high PTFE region. In medium point of PTFE the electrode has maximum performance. The PTFE content that shows maximum performance in the variation of acceleration time is shifted from 35 wt% to 45 wt.% of PTFE content with increasing of acceleration time. In the case of low PTFE

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