Effect of the Porous Structure on the Electrochemical Characteristics of Supercapacitor with Nanocomposite Electrodes Based on Carbon Nanotubes and Resorcinol–Formaldehyde Xerogel

The influence of the porous structure on the electrochemical characteristics of supercapacitors with nanocomposite paper electrodes based on carbon nanotubes and resorcinol–formaldehyde xerogel is studied. The porous structure and hydrophilic–hydrophobic properties of electrodes based on the carbon paper were studied by the method of standard contact porosimetry in the range of pore radii from ~1 to 10 5 nm. The specific surface area ranged from 780 to 960 m 2 /g. The samples contained both hydrophilic and hydrophobic pores. Cyclic capacitance–voltage curves and impedance spectra in 1 M H 2 SO 4 solution showed practically solely the charging of the electrical double layer without a noticeable effect of the pseudocapacitance from Faraday reactions. When the voltage sweep rate was changed by a factor of 100, the values of the equilibrium specific capacitance changed insignificantly (by a factor of 1.25 to 1.36), which indicates the optimality of the porous structure and the dominant contribution of the electrical double layer capacitance to the total capacitance of the supercapacitor. The dependences of the specific volumetric capacitance of the electrode on the logarithm of the voltage sweep rate have a falling linear character for all studied electrodes. A proportionality between the specific capacitance and the electrode specific surface area is demonstrated. This is due to the high porosity of the electrodes (~80 vol %) and the regularity of their porous structure. In addition, according to estimates, from 87 to 89% of the surface was hydrophilic, i.e., can be attributed to functioning pores; only 13 to 11%, to hydrophobic pores. A very high value of the supercapacitor specific power (45.8 kW/kg) was achieved. This shows that the nanocomposite paper is promising for supercapacitors.