Experimental

An electrolyte-exchangeable single cell was designed for this research. First, the cell temperature was raised to 200°C with electrolyte being exchanged to concentrated (105%) phosphoric acid. At 200 °C, l-V characteristics and oxygen-gain were measured under hydrogen/air and hydrogen/oxygen gas flow. After that, cell temperature was lowered to 25°C with electrolyte being exchanged to diluted (45%) phosphoric acid. At 25°C, the surface area of supported catalyst and the double-layer cuiTent of carbon black support were measured by using cyclic-voltammetry (CV) before and after masking Pt surface with CO poisoning (Fig. I), respectively. By repetition of above operations, the electrolyte fill-level was substantially enhanced. Electrode performance at different electrolyte fill-level was investigated, being monitored the electrolyte fill-level by the double-layer current [1]. Pore distribution of electrode and amount of filled electrolyte in electrode were measured by using Hg-porosimeter and chemical analysis with ICP, respectively.

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