Accessing electrode nanostructure with Small Angle Neutron Scattering: a tool to probe the aging effect over the ionomer
Résumé
The low PEFC durability is a critical hindrance for its development. As a crucial component for fuel cell operation, catalysts layers are highly sensible to aging. Decay phenomenon affecting catalysts material are well described in the litterature. However, few is known about the behaviour upon aging of the ionomer contained in the catalyst layer. Ionomer binder is the same material as membrane but its properties and behaviour differ from the bulk component. Therefore, degradation mechanisms may also be different but suffered a lack of interest due to the complex ionomer characterisation. Indeed, as shown by AFM measurements[1], ionomer disperses as an heterogeneous film from 5 to 20 nanometres or creates larger agglomerates around 200 nm. Trapped between carbon and platinum, typical characterisations methods (microscopy, electrochemistry…) needs to be developed in order to probe the ionomer. As a promising path, Small Angle Neutron Scattering allows accessing the ionomer binder structure. Indeed, SANS is the technique of choice to study soft matter and nanoscale structure. Moreover, due to their high interaction with water, Neutrons probe the ionomer nanophase separation structure. These both points established SANS as the best way to study the impact of operation over the ionomer and the catalyst structure. As a recent work, we studied ex-situ catalyst layers with SANS to elucidate the aging affect over the ionomer. Here we will report results obtained from several tests campaigns.