Supercapacitor properties of N/S/O co-doped and hydrothermally sculpted porous carbon cloth in pH-universal aqueous electrolytes: Mechanism of performance enhancement

Carbon cloth (CC) was hydrothermally etched in a highly oxidizable solution to form a porous structure for supercapacitor electrodes on the surface of CC. The oxygen-rich groups on porous CC (OCC) were then partially replaced by N and S elements to produce N/S co-modified porous OCC (MOCC). This method uses a lower temperature than the KOH etching method while maintaining the flexibility and self-supporting properties of CC. The modified MOCC electrodes were investigated as symmetric supercapacitors (SSCs) and compared to conventional collectors such as copper and aluminum foils. The SSCs were tested for electrochemical performance in acidic, alkaline, and neutral electrolytes, enabling them suitable for a wider range of applications. In the acid electrolyte, the device has an area capacitance of up to 3132 mF cm⁻² at 1 mA cm⁻² and a capacitance retention of 91 % after 20,000 cycles at 20 mA cm⁻², outperforming the alkaline and neutral electrolytes. The devices had a maximum volume energy density of 1.82 mWh cm⁻³ and a maximum volume power density of 11.42 mW cm⁻³ when the MOCC electrodes were assembled as symmetrically flexible SCs with an acidic colloidal electrolyte, in addition to passing essential flexibility tests, which proved possible for application in the booming field of flexible energy storage. DFT simulations were conducted on CC, OCC and MOCC, which showed that N/S co-doping enhances the conductivity of OCC and increases the number of active sites, resulting in higher capacitance. This study demonstrates that MOCC can be mass-produced for consistent, high-performance flexible energy storage devices.