Highly Stable Electrochemical Supercapacitor Performance of Self- Assembled Ferromagnetic Q-Carbon

Novel phase Q-carbon thin films exhibit some intriguing features and have been explored for various potential applications. Herein, we report the growth of different Q-carbon structures (i.e., filaments, clusters, and microdots) by varying the laser energy density from 0.5 to 1.0 J/cm2 during pulsed laser annealing of amorphous diamond-like carbon films with different sp3-sp2 carbon compositions. These unique nano-and microstructures of Q-carbon demonstrate exceptionally stable electrochemical performance by cyclic voltammetry, galvanostatic charging-discharging, and electro-chemical impedance spectroscopy for energy applications. The temperature-dependent magnetic studies (magnetization vs magnetic field and temperature) reveal the ferromagnetic nature of the Q-carbon microdots. The saturation magnetization and coercive field values decrease from 132 to 14 emu/cc and 155 to 92 Oe by increasing the temperature from 2 to 300 K, respectively. The electrochemical performances of Q-carbon filament, cluster, and microdot thin-film supercapacitors were investigated by two-electrode configurations, and the highest areal specific capacitance of similar to 156 mF/cm2 was observed at a current density of 0.15 mA/ cm2 in the Q-carbon microdot thin film. The Q-carbon microdot electrodes demonstrate an exceptional capacitance retention performance of similar to 97.2% and Coulombic efficiency of similar to 96.5% after 3000 cycles due to their expectational reversibility in the charging-discharging process. The kinetic feature of the ion diffusion associated with the charge storage property is also investigated, and small changes in equivalent series resistance of similar to 9.5% and contact resistance of similar to 9.1% confirm outstanding stability with active charge kinetics during the stability test. A high areal power density of similar to 5.84 W/cm2 was obtained at an areal energy density of similar to 0.058 W h/cm2 for the Q-carbon microdot structure. The theoretical quantum capacitance was obtained at similar to 400 mF/ cm2 by density functional theory calculation, which gives an idea about the overall capacitance value. The obtained areal specific capacitance, power density, and impressive long-term cyclic stability of Q-carbon thin-film microdot electrodes endorse substantial promise in high-performance supercapacitor applications.

Automated summary

In this study, different Q-carbon structures were fabricated by varying the laser energy density during pulsed laser annealing, and these structures showed potential applications in electrochemical, magnetic, and energy storage devices. The Q-carbon microdots exhibited excellent electrochemical performance and stable magnetic properties, indicating their promise as high-performance supercapacitor electrodes.