Influence of the temperature of heat treatment on phosphoric acid fuel cell cathodes

Abstract

The thermal behaviour of electrode materials during heat treatment from 250-400 ~ was studied. The cathode performance changed by two steps depending on temperature of the heat treatment. At the first step (300 320 ~ polytetrafluoroethylene (PTFE) melted unexpectedly, giving hydrophobic character to the catalyst layer. This change drastically improved the cathode performance. At the second step (340-400 ~ support carbon was oxidized by catalytic action of platinum, increasing the PTFE content from 45 to 83 wt%. This caused a gradual decline in the cathode performance. The poor cell performance of the electrode treated below 300~ is due to the fact that PTFE is not melted at that temperature. Triton X-100 used as a surfactant in the PTFE dispersion disappeared completely from the electrode at these temperatures by oxidation, catalysed by platinum.

AC Impedance Analysis of Bifunctional Air Electrodes for Metal-Air Batteries

“…The mixture was dried for 12 h at 90ЊC, then heated to 350ЊC to fix the PTFE onto the carbon surface. 32,46 The resulting powder was mixed with petroleum (Petroleum special, bp 180-220ЊC, Fluka) in a ratio of 1 to 4 (wt %) to produce a wet dough which was spread out into a thin layer. Petroleum kept the dough wet and smooth during the fabrication process, in which the carbon/PTFE composite was rolled step by step to its final thickness.…”