Effect of sulfated/carboxylated cellulose nanocrystals with different degrees of substitution on the morphology and electrochemical performance of polypyrrole electrodes

Abstract

As a result of different extraction methods, CNCs bear different surface groups with different degrees of substitution (DS), which may affect the electrode properties when incorporated as the reinforcing template in conducting polymer electrodes. After depositing polypyrrole (PPy) electrodes with different CNCs as dopants, we found that the PPy/CNCs electrode structure and electrochemical performance were sensitive to the DS of CNCs sulfate groups, while variation in the DS of carboxylates did not have any significant effect. PPy/CNCs electrodes deposited with carboxylated CNCs and a low sulfate group DS showed a porous and interconnected structure, while PPy/CNCs electrodes deposited with carboxylated CNCs with a high sulfate DS had a dense structure. Higher areal capacitance, higher rate capability, and smaller resistance were achieved with PPy/CNCs electrodes deposited using CNCs bearing carboxylates and a low DS of sulfate groups on CNCs. Cycling studies showed that porous electrodes reduced their charge storage capacity over 3000 cycles, however, dense PPy electrodes prepared using high-sulfate DS CNCs increased their charge storage capacity by 715% (from 0.15 to 1.07 F cm−2) over the first 1200 cycles showing opening of the structure and better electrolyte perfusion. This capacitance then stayed constant for at least another 1700 cycles.