Electrocatalysts and components for polymer-based composite films: pyrolytic carbon deposited on metal and metal oxides derived from hydrotalcite-like materials

Abstract

N- and Fe-containing carbon-based materials were prepared at 600 and 700 °C via catalytic chemical vapor deposition (CCVD) with acetonitrile (as carbon and nitrogen source) with the application of metal/metal oxides generated in situ from Mg–Fe–Al hydrotalcite-like materials (HTs). The impact of synthesis temperature and transition metal (Fe) concentration in a blend of metal oxides derived from HTs on carbon deposit content and its structural ordering, nitrogen doping, location of N-containing groups in graphitic array, morphology and porosity was investigated using XRD, EA, XRF, XPS, SEM, HR-TEM, Raman and Mössbauer spectroscopy, and N2 sorption. Higher synthesis temperature and increased concentration of Fe-containing species occurring in a mixture of metal oxides derived from Mg–Fe–Al HTs enhanced the quantity of carbonaceous product, the mesopore volume and the thickness of graphitic domains occurring in the carbon materials and lowered nitrogen doping extent in carbon framework. Enhanced accessibility to active sites via pore network, as well as, improved electrical conductivity associated with increased graphitic domain thickness and reduced amorphous carbon content were found to be critical factors in their performance for oxygen reduction reaction (ORR) in alkaline electrolyte. No direct correlation between the population of N-containing species and ORR activity is observed but the presence of quaternary N appears to enhance selectivity for the 4-electron pathway. In addition, the influence of the carbon materials dispersed in polymer matrix in polycaprolactone (PCL)-based composite films on bulk (conductivity, dielectric constant) and surface (morphology, topography, roughness and water contact angle) properties was also described.