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    Self-activation of carbons derived from bio-waste cabbage for a green supercapacitor based on seawater electrolyte
    (2024-12-01)
    Phakkhawan, Authit
    ;
    Sakulkalavek, Aparporn
    ;
    Chanlek, Narong
    ;
    Nijpanich, Supinya
    ;
    Ngernyen, Yuvarat
    Carbonized carbons (CC) derived from cabbage were self-activated via a carbonization process at 500–900 °C in Ar. CC synthesized at 800 °C (CC-800), containing KCl, CaCO<inf>3</inf>, Ca(ClO)<inf>2</inf>, K<inf>2</inf>SO<inf>4</inf>, and Ca<inf>5</inf>(PO<inf>4</inf>)<inf>3</inf>(OH), has the highest specific surface area (S<inf>BET</inf>, 130.04 m<sup>2</sup> g<sup>−1</sup>), a high specific capacitance (64.06 F g<sup>−1</sup>), and an excellent rate capability (65.12 %). After washing the CC-800 powder in either deionized (DI) water (AC-DI) or hydrochloric acid (HCl) followed by DI water (AC-HCl-DI), S<inf>BET</inf> values increased to 919.22 and 1146.51 m<sup>2</sup> g<sup>−1</sup>, respectively. KCl, Ca(ClO)<inf>2</inf>, and K<inf>2</inf>SO<inf>4</inf> are removed from the AC-DI, whereas all compounds are washed from the AC-HCl-DI. Removing these compounds enlarges S<inf>BET</inf> values, specific capacitance (114.47 F g<sup>−1</sup> at 0.5 A g<sup>−1</sup>), and rate capability (68.95 %). A high capacitance retention of 97.56 % after 20,000 cycles was achieved from the AC-HCl-DI electrode with 6 M KOH. 0.6 M NaCl and seawater were applied as green electrolytes with the AC-HCl-DI electrode, resulting in the promising specific capacitance of 116.89 and 102.21 F g<sup>−1</sup> at 0.5 A g<sup>−1</sup>, respectively. Symmetric AC-HCl-DI/seawater/AC-HCl-DI cell gives a high energy density of 2.32 Wh kg<sup>−1</sup> at a large power density of 0.25 kW kg<sup>−1</sup>. The four serial AC-HCl-DI/seawater/AC-HCl-DI coin cells could light an LED over 60 s.
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    Investigation of Radiation Effect on Structural and Optical Properties of GaAs under High-Energy Electron Irradiation
    (2022-09-01)
    Phakkhawan, Authit
    ;
    Sakulkalavek, Aparporn
    ;
    Buranurak, Siritorn
    ;
    Klangtakai, Pawinee
    ;
    Pangza, Karnwalee
    A systematic investigation of the changes in structural and optical properties of a semi-insulating GaAs (001) wafer under high-energy electron irradiation is presented in this study. GaAs wafers were exposed to high-energy electron beams under different energies of 10, 15, and 20 MeV for absorbed doses ranging from 0–2.0 MGy. The study showed high-energy electron bombardments caused roughening on the surface of the irradiated GaAs samples. At the maximum delivered energy of 20 MeV electrons, the observed root mean square (RMS) roughness increased from 5.993 (0.0 MGy) to 14.944 nm (2.0 MGy). The increased RMS roughness with radiation doses was consistent with an increased hole size of incident electrons on the GaAs surface from 0.015 (0.5 MGy) to 0.066 nm (2.0 MGy) at 20 MeV electrons. Interestingly, roughness on the surface of irradiated GaAs samples affected an increase in material wettability. The study also observed the changes in bandgap energy of GaAs samples after irradiation with 10, 15, and 20 MeV electrons. The band gap energy was found in the 1.364 to 1.397 eV range, and the observed intense UV-VIS spectra were higher than in non-irradiated samples. The results revealed an increase of light absorption in irradiated GaAs samples to be higher than in original-based samples.