Experimental

To clarify the effect of the degradation of catalysts themselves on the electrode performance or the life-time, catalysts in different degradation states prepared by electrochemical treatments of same mother catalysts under different conditions were examined in gas-diffusion electrodes loaded them.

1) Preparation of catalysts in different degradation states

The mother catalyst was an as-received Pt/Ni/Co catalyst (ca. 2/1/1 gross atomic ratio)

supported on a carbon black (CB) (ca. 100m2/g). The loading at the catalyst was 20 percent (w/o) in platinum weight.

The paste of catalysts mixed with phosphoric acid (ca.l05%H3P04) was sandwiched between the two sheets of carbon paper (thickness=0.1mm) and was mounted into a SiC matrix type cell as a working electrode. Before electrochemical treatment, catalysts were held at 120°C with air flow humidified at room temperature for 14 hours which was a similar condition to the initial electrolyte filling in practical PAFCs. Electrochemical treatments were performed in the cell apparatus controlled at different temperature and potential conditions for 48 hours. A gas diffusion electrode, which is same as a conventional PAFC anode, served both as reversible hydrogen reference electrode (RHE) and counter electrode. The concentration of phosphoric acid electrolyte was controlled at 100%H3P04 by humidification.

2) Characterization of prepared catalysts

The electrochemical metal surface area (Spt), double layer current (IDL) under CO poisoned condition, which corresponds to surface area of the CB support wet with electrolyte [1], were measured by using cyclic voltammetry (CV). Spt was calculated from the amount of charge of hydrogen adsorption peak in CV assuming 210/i C/cm2. Idl was defined as a width (mA/mg-C) of C V at 450m V vs RHE in a double layer region under CO poisoned condition. Potential sweep rate was 50mV/s.

gas outlet gas diffusion electrode gas inlet

. carbon plate electrolyte outlet

PIPE sheet.

carbon paper '

gas outlet gas diffusion electrode gas inlet electrolyte outlet

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