EFFECT OF CONCENTRATION OF SURFACE ACIDIC FUNCTIONAL-GROUPS ON ELECTRIC DOUBLE-LAYER PROPERTIES OF ACTIVATED CARBON-FIBERS

The relationship between electric double-layer properties in an organic electrolytic solution and a concentration of surface acidic functional groups (surface acidity) of a phenolic resin-based activated carbon fiber (ACF) was characterized in a system of ACF/electrolytic solution/ACF The lower surface acidity of ACF resulted in the lower apparent leakage current of the electric double layer. The capacitance and the dc resistance of the layer were almost independent of the surface acidity. Further heat treatment of ACF in nitrogen atmosphere decreased the surface acidity of ACF. Types of C-O bonds in surface acidic functional groups were identified as carboxy and ester groups for ACF as-prepared and as phenolic hydroxy and quinone groups for ACF heat treated. The ACF obtained from the phenolic resin-based fibers showed an extremely low surface acidity in comparison with other kinds of ACF. The polarizable electrodes of the phenolic resin-based ACF resulted in electric double-layer capacitors with high capacitance and low leakage current. © 1990.