Oxygen reduction catalysts in PEFCs have traditionally contained relatively high amounts of platinum or other platinum group metals. There has been a drive towards reducing the loading, but a promising alternative has been discovered in the form of iron and nitrogen-doped carbon. However, their activity is still not acceptable, and their improvement is hampered by the lack of knowledge about the chemical structure of the materials and in particular the active site(s). There is still disagreement over whether the active site is organic or metallic, or even both.

Temperature-programmed techniques such as temperature-programmed desorption (TPD) and temperature-programmed reaction spectroscopy (TPRS) are powerful techniques used in conventional catalysis for probing active sites. Molecules which interact with the active sites are adsorbed on the catalyst, then the system is heated and the desorption of the initial molecule or products can be measured by mass spectrometry. These techniques allow quantification of number of active sites, heats of desorption and reaction, assessment of reaction mechanisms and studies of poisoning behaviour.

This study reports extensive TPD and TPRS work done on an iron and nitrogen doped carbon-based oxygen reduction catalyst. Interactions between various molecules and the active site(s) on the catalyst have been studied and quantified. Correlations between TPRS and TPD studies and electrochemical studies have been made from fresh, aged and poisoned materials, and these have been compared to studies on similar materials containing either no iron, or no iron and nitrogen. In addition, ex situ measurements including EXAFS and Mössbauer on the same materials will be reported on. Together these experiments are used to draw conclusions about the nature of the active site(s) in these materials.