Sang Jae Kim

Electrochemical performance of an asymmetric supercapacitor based on graphene and cobalt molybdate electrodes

In this article, we report the fabrication and electrochemical performance of asymmetric supercapacitors (ASCs) based on a reduced graphene oxide (rGO) negative electrode and a cobalt molybdate (CoMoO4) positive electrode. The rGO and CoMoO4 electrode materials were synthesized by hydrothermal and sonochemical methods, respectively. Physico-chemical characterization techniques such as X-ray diffraction, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and nitrogen adsorption–desorption isotherm analysis were used to characterize the electrode materials. The rGO nanosheets and CoMoO4 nanostructures delivered a specific capacitance of about 168.8 and 98.34 F g−1, respectively measured in a three electrode system. The rGO‖CoMoO4 ASC device demonstrated a maximum specific capacitance of 26.16 F g−1 (at a current density of 0.5 mA cm−2), an energy density of 8.17 W h kg−1, and a maximum working voltage of 1.5 V. The fabricated device possessed excellent capacitance retention of about 85% after 4000 cycles (at a current density of 1.0 mA cm−2) suggesting the superior cyclic stability of the fabricated ASC device.

Defect-induced metallic-to-semiconducting transition in multilayer graphene

We investigate the electrical transport properties of multilayer graphene (MLG) following irradiation with Ar plasma. The plasma induces defects, including vacancies, voids, and nanoholes, which altered the resistance of the MLG. The resulting defect-rich MLG device exhibits an asymmetric ambipolar behavior, with a strong p-doping effect, which considerably deteriorates the electron conductivity, implies defect generation on the MLG surface. The pristine MLG was metallic; however, the resulting defect-rich MLG following plasma treatment exhibited a semiconductor-like temperature dependence of the resistance. Thus, MLG with morphological disorder exhibits a metallic-to-semiconductor transition in the resistance as a function of temperature.