The effect of the functionalization of carbon nanofibers on their electronic conductivity

The effects of the functionalization of carbon nanofibers (CNFs) on their electronic conductivity, in addition to their physico-chemical properties have been studied. Oxygen surface groups have been created on the surface of three CNFs with different properties, following three oxidation treatments with diverse severity. The oxygen content increased from two to six times the original content, depending on the CNF texture, from 1.5-2.6 wt.% up to 15.1 wt.%. Whereas some important properties are not significantly modified after functionalization (texture, crystalline structure, etc.), other properties like the electronic conductivity are affected depending on the extent of the process. The electronic conductivity of CNFs decreases from 200-350 S m-1 up to 20-100 S m-1 (the precise value depends on carbon crystallinity and compaction degree) when surface oxygen content increases from 1.5 wt.% to 5 wt.%. A further oxidation degree leads to a 90% decrease in conductivity, and in the end can even destroy the original fibrous structure. As a first approach, oxidizing at room temperature with rather strong acid solutions is a better strategy to create functional groups and maintain the electronic conductivity than increasing the process temperature with less severe oxidizing agents.