PLATINUM UTILIZATION IN A PHOSPHORIC-ACID FUEL-CELL

We evaluated the platinum utilization in a gas diffusion electrode of a phosphoric acid fuel cell using a geometrical and an electrochemical methods. The results show that the platinum surface area is utilized by around 50% compared with nominal platinum surface area. The accelerating impregnation of the acid into the electrode led the same EC-MSA value among various hydrophobic electrodes (in Out-of-Cell Test:OCT). This shows that the PTFE content and the heat-treatment temperature are not intrinsically significant for EC-MSA and that the impregnation procedure is of more importance. The process conditions such as a PTFE content and heat-treatment temperature are considered to only define the impregnation rate. It was found that the EC-MSA was decreased at the beginning of operation in the real cell and that the value approached to the value (around 20m(2)/g) of OCT. The present results suggests that the dispersion of PTFE in the gas diffusion electrode defines the maximum platinum utilization (around 50%) and that the real utilization in the cell depends on the impregnation process of the cell. An improved dispersion of PTFE is expected and the corrosion reaction of carbon support is suppressed to enhance the cell performance.