Urea-treatment of CoOx carbon nanofibers to improve the electrochemical performance of supercapacitor using aqueous electrolytes

Abstract

Supercapacitors (SCs) play a crucial role in flexible electronics, necessitating innovative approaches to enhance surface faradaic reactions and minimize faradaic diffusion while using aqueous electrolytes. Thus, the urea treatment of cobalt oxide (CoOx)-decorated carbon nanofibers (CNFs) is proposed in this study to decrease the contribution of faradaic diffusion-limited current. Flexible CoOx/CNF electrodes were obtained by annealing ZIF-67-grafted polyacrylonitrile (PAN) fibers via a wet chemical method. The urea treatment of CoOx/CNFs increased the content of sp2-hybridized carbon and pyridinic nitrogen, as confirmed by X-ray photoelectron spectroscopy, effectively enhancing conductivity and pseudocapacitive charge storage capability via nitrogen doping. Notably, urea-treated CoOx/CNF electrode samples exhibited a capacitance of 750 mF cm−2 at a scan rate of 10 mV s−1, while retaining more than 81 % capacitance at a higher scan rate of 100 mV s-1. The cyclic voltammetry curves during variable bending angle testing (0°, 45°, and 90°) exhibited negligible changes, indicating the excellent flexibility of the SCs. The CoOx/CNFs and urea-treated CoOx/CNFs exhibited 80 % and 91 % capacitance retentions, respectively, after 10,000 galvanostatic charge and discharge cycles. Furthermore, the attained energy densities of 76 and 61 µWh cm−2 at the respective power densities of 2 and 20 mW cm−2 indicated the excellent electrochemical performance of the optimal urea-treated CoOx/CNF electrode.