Carbide derived carbons investigated by small angle X ray scattering Inner surface and porosity vs. graphitization

Small angle X ray scattering SAXS was used to study the nanostructure of Mo2C derived carbon powders CDC synthesized at five different chlorination temperatures. The SAXS intensities have two contributions i a fluctuation contribution from small partially graphitized areas that gives quantitative information about the extent of graphitization, and ii the scattering from the pores. The fluctuation contribution that scales with q2 was quantified in term of a length parameter lR and a disorder parameter that can directly be correlated with the increasing graphitization with increasing temperature. The specific inner surface area of the CDC together with the volume fraction f of the pores increases with the chlorination temperature until 900 C, followed by the significant decrease of both parameters at 1000 C. Further analysis led to the conclusion that CDC obtained at 600 and 700 C are ultramicroporous systems with slit pores having an average size of the order of 0.6 nm. CDC obtained at a high chlorination temperature have pores with sizes between 1 and 3 nm that are of the same size as the walls between the pores. A first comparison demonstrates that the stored energy Emax is directly proportional to the anisometry of the pores embodied in the ratio lc lp obtained by SAX