Influence of Loading on the Activity and Stability of Heat‐Treated Carbon‐Supported Cobalt Phthalocyanine Electrocatalysts in Solid Polymer Electrolyte Fuel Cells

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Abstract
The influence of loading on the activity and stability of heat‐treated carbon‐supported cobalt phthalocyanine electrocatalysts for oxygen reduction was studied. The Co loading on the carbon support was varied from , while heat‐treatment temperatures ranging from 500 to 1100δC were studied. There is an optimum value of the Co loading on the carbon support (about ) over which the catalytic activity of the Co on carbon catalyst decreases. This trend is observed in both half‐cell (rotating disk electrode measurements) and fuel cell measurements. The optimum value of the Co loading on the carbon support is independent of the heat‐treatment temperature. An explanation is proposed for this observation. We have also performed short‐term (15 to 18 h) life tests with the Co on carbon‐support materials heat‐treated at various temperatures. It is shown that the current density lost after 18 h of operation is a function of the heat‐treatment temperature being lower the higher the temperature. The observed increase in the stability of the material with the heat‐treatment temperature is best explained by considering the protective role played by the graphitic‐like layer surrounding the Co metal particles.