Results And Discussion

The relationship between the double-layer current (Idl) which corresponds to the electrolyte fill-level and the oxygen-gain which corresponds to the diffusion-polarization was shown in Fig.2. As the double-layer current increases, the oxygen-gain decreases first. During this process, the fill-level was proceed to an appropriate level. As the double-layer current increases more, the oxygen-gain shows a minimum value, then increases. During this process, the fill-level exceeds the appropriate level. So, the electrodes at high gas-diffusion loss-level (oxygen-gain=121mV, or Idl=4.5mA/cm2) and at low gas-diffusion loss-level (oxygen-gain=91mV, or ldl=3.7mA/cm2), were investigated regarding the dependency of the performances upon the electrolyte fill-levels, respectively. Results were shown in Fig.3. In the case of electrolyte fill-level (vs. total pore volume), the fill-level of the electrode at high gas-diffusion loss was much higher than that of low gas-diffusion loss. For the detail discussion, the electrolyte fill-level was measured, combined with the measurement of pore size distribution, i.e., electrolyte distribution into the primary and secondary pores. The primary pores concerned to be formed between the primary CB particles and acting as reaction sites, and secondary pores to be formed between the CB agglomerates and acting as gas-networks, respectively [2]. At high gas-diffusion loss electrode, the electrolyte fill-level of secondary pores (70%) was extremely high in comparison with that of primary pores (45%). On the other hand, at low gas-diffusion loss electrode, the electrolyte fill-level of the secondary pores was very low (16%), in spite of the electrolyte fill-level of the secondary pores (44%) being equal to that of high gas-diffusion loss electrode. As indicated above, it was clarified that the electrolyte fill-level of the primary pores acting as reaction sites is independent to gas-diffusion loss, and the electrolyte filling to the secondary pores acting as gas-networks inhibits gas diffusion to reaction sites, resulting in an increase of gas-diffusion loss. It was also clarified that the utilization of platinum clusters was constant (45%) at these electrodes.

0 0

Post a comment