Nickel MXene Nanosheet and Heteroatom Self-Doped Porous Carbon-Based Asymmetric Supercapacitors with Ultrahigh Energy Density

For high-energy-density supercapacitors, two-di-mensional (2D) MXenes are being increasingly explored due to their inherent conductivity and excellent chemical properties. However, MXenes failed to achieve high power density and exceptional stability. Addressing this, we report the fabrication of an asymmetric supercapacitor with nickel MXene (cathode) and nitrogen (N), sulfur (S), and phosphorus (P) self-doped biomass-derived activated carbon (anode). Detailed structural and chemical characterization studies reveal layered nanosheets in NiMX caused due to solvothermal etching cum exfoliation and unique micro- mesopore distribution in the optimized Euphorbia milii plant leaf-derived heteroatom self-doped activated carbon (EMAC-700) because of KOH activation. NiMX and EMAC-700 delivered high capacitances of 474.3 and 575.8 F/g, respectively, at 1 A/g with a 6 M KOH electrolyte. This is attributed to the pseudonature of NiMX and the presence of heteroatoms and the large surface area (2349 m2/g) of EMAC-700, facilitating fast electrolytic ion transfer. Finally, an asymmetric device with NiMX//EMAC configuration in 6 M KOH delivered a 152.6 F/g cell capacitance at 0.5 A/g under 0-1.5 V. Additionally, an ultrahigh energy density of 47.6 W h/kg at a 375 W/kg power density was achieved along with an 81.7% capacitance retention after 30,000 cycles at 15 A/g, signifying its potential for next-generation energy storage applications.

Automated summary

In this study, an asymmetric supercapacitor was fabricated using nickel MXene as the cathode and self-doped biomass-derived activated carbon with nitrogen, sulfur, and phosphorus as the anode. The results showed that this supercapacitor exhibited high energy density and stability, and demonstrated excellent ionic transfer performance. Therefore, this research is of great importance for next-generation energy storage applications.