Post-Treatment of Carbon Nanotubes Based Electrodes to Realize Low Self-Discharge Supercapacitors

In supercapacitor research, the emphasis is often on enhancing capacitance, while self-discharge is frequently neglected, despite its potential to hinder long-term energy storage. This study investigates a post-annealing process applied to carbon nanotube (CNT) supercapacitor electrodes to lower the self-discharge, conducted in a chemical vapor deposition chamber using hydrogen $\left(\mathrm{H}_{2}\right)$ and nitrogen $\left(\mathrm{N}_{2}\right)$ gases. The optimal annealing parameters were established at $500^{\circ} \mathrm{C}$ for 30 minutes with a $\mathrm{H}_{2}: \mathrm{N}_{2}$ ratio of $20 \mathrm{sccm}: 200 \mathrm{sccm}$. This post-treatment resulted in a significant reduction in self-discharge, decreasing from 91.4% to 29.1% of the initial 2.7 V charge after 16 hours, translating to a 62.3% improvement. Additionally, the supercapacitor with annealed electrodes demonstrated 6.6% better self-discharge performance compared to a commercial capacitor.