Activated carbons derived from sugarcane bagasse for high-capacitance electrical double layer capacitors

Activated carbon (AC) from sugarcane bagasse was prepared using a simple two-step method of carbonization and chemical activation with four different activating agents (HNO₃, H₂SO₄, NaOH, and KOH). Amorphous carbon structure as identified by X-ray diffraction was observed in all samples. Scanning electron microscopy revealed that the AC had more porosity than the non-activated carbon (non-AC). Specific capacitance of the non-AC electrode was 32.58 F g^?1 at the current density of 0.5 A g^?1, whereas the AC supercapacitor provided superior specific capacitances of 50.25, 69.59, 109.99, and 138.61 F g^?1 for the HNO₃ (AC-HNO₃), H₂SO₄ (AC-H₂SO₄), NaOH (AC-NaOH), and KOH (AC-KOH) activated carbon electrodes, respectively. The AC-KOH electrode delivered the highest specific capacitance (about 4 times of the non-AC electrode) because of its good surface wettability, the largest specific surface area (1058.53 m² g^?1), and the highest total specific pore volume (0.474 cm³ g^?1). The AC-KOH electrode also had a great capacitance retention of almost 100% after 1000 GCD cycles. These results demonstrate that our AC developed from sugarcane bagasse has a strong potential to be used as high stability supercapacitor electrode material.

     

Thermal stability improvement of dielectric properties and non-ohmic characteristic of CaCu3+xTi4O12 ceramics via a Cu-nonstoichiometric approach

In this work, the effects of Cu composition on the thermal stability of the dielectric and nonlinear properties of CaCu_3+xTi₄O₁₂ (?0.2 ≤ x ≤ 0.2) ceramics obtained via a polymer-pyrolysis chemical process were studied. The mean grain sizes of Cu-stoichiometric (x = 0), Cu-deficient (x < 0) and Cu-excess (x > 0) CaCu_3+xTi₄O₁₂ ceramics were found to be ~3.2, ~3.4 and ~3.7 μm, respectively. Interestingly, very good dielectric properties (0.020 ≤ tanδ ≤ 0.038 and 4000 ≤ ε′ ≤ 7065) were attained in CaCu_3+xTi₄O₁₂ (?0.2 ≤ x ≤ 0.1, excluding x = 0.2) ceramics. Moreover, the variation of dielectric constant (ε′) within a limit of ±15% (Δε′_{± 15%}) over a wide temperature range (T_R) of ?70 – 220 °C with low tanδ < 0.05 (tanδ_<0.05) over a T_R of ?70 to 80 °C were achieved in a CaCu_2.8Ti₄O₁₂ ceramic. These results suggest that this ceramic could be applicable for X9R capacitors and energy storage devices that require high thermal stability. Additionally, the nonlinear properties of Cu-nonstoichiometric ceramics could be improved when compared with those of the Cu-stoichiometric material. The incremental changes of dielectric and nonlinear properties of CaCu_3+xTi₄O₁₂ (?0.2 ≤ x ≤ 0.2) ceramics revealed the significant role of Cu composition on grain boundary resistance (R_gb), which was confirmed by impedance spectroscopy analysis. In addition, XANES results revealed the proper ratios of Cu⁺:Cu²⁺ and Ti³⁺:Ti⁴⁺ found in these ceramics, indicating the semiconducting behavior of these grains.     

Influence of SCN− moiety on CH3NH3PbI3 perovskite film properties and the performance of carbon-based hole-transport-layer-free perovskite solar cells

Journal of Materials Science: Materials in Electronics - CH3NH3PbI3 perovskite films were prepared via a hot-casting method using six different CH3NH3I, PbI2 and Pb(SCN)2 solutions. Surface...