Electron microscopy study of new composite materials based on electrospun carbon nanofibers†
To create a new type of catalytic gas diffusion layer for a high-temperature hydrogen/air polymer-electrolyte membrane fuel cell (HT-PEMFC), a new electrospun carbon nanofiber (CNF)-based platinized nanocomposite was formed. Its structure was studied by scanning, high resolution transmission and scanning transmission electron microscopy, electron diffraction, EDX analysis, electron tomography and Raman spectroscopy. The temperature dependence of the morphology and structure of carbon nanofibers was investigated: high annealing temperatures (1200 and 2800 °C) led to graphitization with straight graphene layer sets in nanofiber bodies, whereas curly graphene layer sets were observed for Fe-containing annealing. Platinization of CNFs with further heating at elevated temperature (280 °C) led to the formation of spherical nanoparticles of 3.0 nm diameter, while at room temperature “finger”-like nanoparticles with a length up to 20 nm grew along <111> directions. Structural evolution of the nanofibers resulted in an increase of their porosity, electroconductivity and thermal stability, as well as formation of a CNF surface relief providing a smoother and more uniform platinum nanoparticle cover. The most uniform one was obtained on carbon fibers synthesized from a polymer mixture and further graphitization in the presence of iron nanoparticles.