Nitrogen-doped porous carbon electrode for aqueous iodide redox supercapacitor

The incorporation of redox-active anions into aqueous electrolytes endows electrodes with enhanced specific energy density for supercapacitors. However, the congruent relationship between the redox chemistry of electrolytes and electrode surfaces is still not well understood. Herein, two-dimensional nitrogen-doped porous carbon nanosheets (denoted as NC-x with x being the carbonization temperature in Degree Celsius) are systematically synthesized by using general dual-crystals templating assisted strategy with pore structure and surface composition optimized. Employed as both positive and negative electrodes, the as-prepared NC-900 with a large specific surface area and ample graphitic N sites shows a high specific capacitance of 251 F g⁻¹ with a voltage window of 1.6 V and energy density of 22.4 Wh kg⁻¹ associated with 86.5% capacity retention after 30,000 cycles using aqueous iodide redox electrolyte. The experimental and theoretical analyses reveal the contributions of nitrogen configurations on the carbon scaffolds to accelerate the redox chemistry of iodides. The enhanced redox performance of the porous carbon nanosheets is linearly proportional to the graphitic N content, which is consistent with the large electron-donating area and the strong adsorption capacity towards iodine species at the graphitic N sites. This work shows a new design strategy of carbon electrodes for high-performance supercapacitors with the aqueous redox electrolytes.