High-frequency supercapacitors with phosphorus-doped Ketjen black

Compact supercapacitors (SCs) have attracted attention for their great potential to replace bulky aluminum electrolytic capacitors (AECs) in alternating current (AC) line filtering applications. Herein, the fabrication of a high-frequency SC is reported using Ketjen black (KB) nanoparticles doped with phosphorus (P) to achieve a high areal capacitance of up to 2.26 mF cm⁻² along with a high-rate capability, with a phase angle of –80.2° at 120 Hz. The high performance of the phosphorus-doped KB (designated PKB) SC with a 6 M KOH aqueous electrolyte is associated with its increased surface wettability and additional capacitive sites provided by the P-doping. Density functional theory (DFT) calculations further indicate that the P-doping enhances the interactions between the electrolyte ions and the carbon surface, thus leading to an improved electrochemical performance. These results suggest that the P-doped carbon-based SC could be highly favored in replacing conventional AECs in various high-frequency electronic devices.