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carbon plate test electrode

,electrolyte inlet 7 PTFE packing v electrolyte matrix gas outlet test electrode carbon plate

Fig. 1 Structure of electrolyte-exchangeable cell

The CV measurements were performed in 45% h3po4 using an electrolyte exchangeable cell (Fig.l). The catalysts sandwiched between a carbon paper wet-proofed with polytetrafluoroethylene (PTFE) (gas side) and a SiC electrolyte matrix attached with a non-wet-proofed carbon paper (electrolyte side) was set as a test electrode. A gas diffusion electrode (same as conventional PAFC anode) was used as a counter electrode. RHE connected to the electrolyte outlet was used as a reference electrode.

X-ray diffraction analysis (XRD) were performed to determine the average crystalline sizes of each phase of Pt[Co*Ni], PtjfCo'Ni] and Pt.

3) Evaluation of electrode

The degraded catalyst was fabricated into a PTFE-bonded catalyst layer on the carbon paper substrate wet-proofed with PTFE. Each electrode had a constant platinum loading of 1.0mg/cm2 and about 38 w/o PTFE for carbon support.

By using electrolyte-exchangeable cell mentioned above, the electrode performances (I-V characteristics and oxygen-gain) were measured in about 100% h3po4 at 200°C. Then Ini. and Spt were measured by using cyclic voltammetry (CV) in 45% H3P04 at 25°C in order to know the electrolyte fill-level and the catalyst utilization.

During the repetition of these measurements, a performance was changed with the increase of the electrolyte fill-level from starved level to appropriate level and subsequently to excessive level.

RESULTS AND DISCUSSION 1) Metal surface area

Table 1 shows the values of surface area determined by electrochemical method for catalysts degraded under various conditions.

Table 1 Metal surface areas of catalysts treated under different temperatures and potentials for 48 hours _

Temperature (°C)

Potential (VvsRHE)

Metal surface area (SpO (mVg-Pt)

before electrochemical treatment*

0 0

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