Synthesis, characterization, and electrochemical capacitance of amino-functionalized carbon nanotube/carbon paper electrodes

Amino-functionalization of carbon nanotubes (CNTs) attached to carbon paper (CP) has been achieved using one synthesis protocol: (i) chemical oxidation, (ii) acyl chlorination, and (iii) amidation. The amidation reaction of the carboxylic groups in oxidized the CNT/CP hybrids enables the formation of terminal amino groups on the CNT sidewalls. The functionalized CNTs were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, thermal programmed desorption, and N2 adsorption. The cyclic voltammetry curves of an amino-modified CNT-based capacitor showed a continuum of double-layer and pseudocapacitive behavior. The presence of surface oxides and amides on CNTs imparts not only hydrophilic coverage for the formation of double-layer (double-layer capacitance) but also active sites for the redox reaction (pseudocapacitance). Based on the result of the charge/discharge cycling test, the N-modified CNT/CP capacitor exhibits an enhanced capacitance, high-rate capability, and capacitance stability with high coulombic efficiency.