Abstract: Fuel cells are electrochemical devices that convert chemical energy directly into electricity. This environment-friendly technology plays an important role in the future energy landscape. Proton-exchange fuel cells are especially attractive energy devices for automotive propulsion because of their high energy efficiency. Today, platinum-based catalysts are the state of the art, but they contribute to a huge extent to the overall costs of a fuel cell system. Based on this, there are efforts on all continents to find suitable alternatives.

In this work, I would like to present the recent outcome of our development with respect to catalyst preparation and structural characterization. Nuclear inelastic scattering (NIS, also known as NRVS and NRIXS) in combination with low-temperature Mössbauer spectroscopy was used to identify all species present in Fe-N-C catalysts. In situ and operando Mössbauer spectroscopy was used to monitor the iron species that are formed during electrochemical conditioning, to identify the exact coordination environment and possible intermediates of the ORR. On the basis of this, we suggest a reduction cycle on Fe-N-C catalysts and highlight the main difference between our model and the current status discussed in literature.