Stickstoff- und Eisen- dotierte Kohlenstoff-Aerogele

Abstract

The aim of this work is the development of nitrogen- and iron-doped carbon aero-gels as substitutes for platinum-containing catalysts in the High-Temperature Poly-mer Electrolyte Membrane Fuel Cell (HT-PEMFC). For this purpose, melamine-formaldehyde (MF)-aerogels with different compositions (variation of mela-mine/formaldehyde and melamine/catalyst ratios) were prepared and then carbon-ized at 700 °C to form a nitrogen-containing carbon aerogel. Iron doping is carried out with ferrocene, either during carbonization of the MF-aerogels or during a sec-ond carbonization of the nitrogen-containing carbon aerogels. Noticeable is, that during the synthesis of the MF-aerogels, the gelation time was very different – from few seconds to several minutes, making handling of samples as well as possible upscaling difficult. The carbonization of the MF-aerogels showed that the carbonization parameters have a great influence on the carbon aerogels. The heating rate of 10 Kmin-1 re-sults in foam-like carbon aerogels with a low surface area of less than 75 m²g-1 and a high nitrogen content of up to 50 wt.-%. Reduced heating rate of about 1,75 Kmin-1 led to carbon aerogels with a higher surface area of up to 644 m²g-1 and a nitrogen content of up to 23 wt.-%. A possible reason for this behavior could be the greater gas evolution at higher heating rates, leading to pore collapse and inflation of the samples. Iron doping of the MF-aerogels was successfully carried out. The iron content ranges from 4,1 to 28,9 wt.-%, which is much higher than the iron content of the iron-doped carbon aerogel. In addition, the samples show a lower mass loss of 75 % in comparison to the carbonized MF-aerogels without ferrocene. The specific surface area, compared to the nitrogen-containing carbon aerogels, remained ap-proximately the same. However, the iron-doped MF-aerogels show a very low mesopore volume as well as a very low conductivity of less than 10 Sm-1. In the TEM analysis, it can be seen that no iron-nanoparticles and carbon nanotubes were formed in the material, which could make the material suitable as a catalyst. How-ever, the performance still needs to be analyzed by further tests such as rotating ring-disk electrode (RRDE) and gas diffusion electrode (GDE).