Experimental and Theoretical Investigation of Porous Carbon Nanospheres for Supercapacitor Application

Activated carbon holds a promising avenue in the context of energy storage because of its special attributes like high surface area, large pore volume, and ease of preparation. Herein, we synthesized the activated carbon from low-cost candle soot and employed it as an electrode for supercapacitor application. Activation resulted in a high specific surface area of 1679 m² g⁻¹ The electrochemical properties of activated candle soot (ACS) and unactivated candle soot (CS) are evaluated in a three-electrode setup using 1 M H₂SO₄ as an electrolyte. ACS and CS exhibited specific capacitance of 467 and 180 F g⁻¹ at a current density of 2 A g⁻¹, respectively. The improved electrochemical performance of ACS is attributed to an increase in surface area upon activation, which acts as a reservoir to accommodate a large number of electrolyte ions. Furthermore, two-electrode studies of ACS symmetric cells revealed the extraordinary capacitance of 397 F g⁻¹ at 1 A g⁻¹. The ACS system retained a capacitance of 82% for 10,000 cycles at a high current density of 10 A g⁻¹. This system exhibited a specific energy of 19.8 Wh kg⁻¹ at a specific power of 574.8 W kg⁻¹. We performed density functional theory (DFT) simulations to validate the experimental observations and found that the quantum capacitance of ACS is greater than that of CS. Furthermore, the barrier energy for ionic diffusion across the surface of ACS is lower than that of CS, indicating improved mobility upon activation.