Variability within a single type of polyacrylonitrile-based graphite felt after thermal treatment. Part II: chemical properties

Graphite felts are often activated thermally before use in electrochemical reactors. This has the effect of improving wetting and decreasing charge-transfer resistance. In part I of this study, considerable variations were observed between two polyacrylonitrile (PAN)-based felts from different production charges after thermal activation, despite both charges being of the same type of felt from one supplier. A difference due to bulk crystallinity or due to pronounced core-rim structures of the fibres has been excluded. In this second part a limitation from tarry coatings, which are a possible side products of graphitization, could not be corroborated. However, differences were ascribed to variations in the surface chemistry, which was characterised by Boehm method titration and cyclic voltammetry. The composition of the oxides is discussed together with the possible role they play in the activation and wetting of the felts. The rather high amount of oxides suggests that the Boehm method measures subsurface groups in addition to surface groups. The wetting quality of activated felts can be correlated well with the concentration of neutral quinone groups, characterised by cyclic voltammetry.