The investigation of activated carbon by K2CO3 activation: Micropores- and macropores-dominated structure.

In this study, the K2CO3 activation of bamboo was investigated in detail, and the structure and properties of the prepared activated carbons were tested for the feasibility of CO2 capture application and the potential for both ion and bacteria adsorption for use in the field of hazardous wastewater treatment. Activated carbons were produced with different activator ratios, from 0.5 to 6 according to the sample mass ratio. The ratio of H or O to C (H/C or O/C) increased with the increasing amount of K2CO3 added for the activation. The samples had a highly-porous microporous structure, in which the micropore volume was calculated to be 0.6 cm3 g-1 by the DR method of the CO2 adsorption isotherm at 298 K. The BET surface area and total pore volume estimated from the N2 adsorption isotherms at 77 K of the activated materials increased according to the increase of the K2CO3 impregnation ratio to a maximum value of 1802 m2 g-1 and 0.91 cm3 g-1, respectively. Moreover, the K2CO3-activated samples had a specific morphology, that is, macropores which are presumed to be derived from bubbles. The X-ray-CT images showed that the bubble-like structure is not only on the surface but also inside the samples. The results of gas adsorption methods, mercury porosimetry, and SEM showed the co-existence of micropores (<2 nm) and macropores (100-10,000 nm). The results highlighted the unique pore structure, that is, the coexistence of micropores and macropores that would contribute to forming solutions for carbon sequestration in the atmosphere and wastewater treatment.

High-Temperature Degradation Tests on Electric Double-Layer Capacitors: The Effect of Residual Voltage on Degradation.

The demand for electric double-layer capacitors, which have high capacity and are maintenance-free, for use in a variety of devices has increased. Nevertheless, it is important to know the degradation behavior of these capacitors at high temperatures because they are expected to be used in severe environments. Therefore, degradation tests at 25 °C and 80 °C were carried out in the current study to analyze the degradation behavior. Steam-activated carbon, Ketjen black, and PTFE were used as the electrodes, conductive material, and binder, respectively, and KOH was used as the electrolyte. The impedance and capacitance were calculated from the voltage and current in the device using the alternating current (AC) impedance method. The results showed that the impedance increased and the capacitance decreased over 14 days at 80 °C, which is the inverse of what we observed at 25 °C. Rapid degradation was also confirmed from the 80 °C degradation test. The residual voltage after measuring the current and voltage was a prominent factor influencing this rapid degradation.

Modeling of Equivalent Circuit Analysis of Degraded Electric Double-Layer Capacitors.

The demand for electric double-layer capacitors (EDLCs) has recently increased, especially for regenerative braking systems in electric or hybrid vehicles. However, using EDLCs under high temperature often enhances their degradation. Continuously monitoring EDLC degradation is important to prevent sudden malfunction and rapid drops in efficiency. Therefore, it is useful to diagnose the degradation at a lower frequency than that used in charge/discharge. Unused and degraded EDLCs were analyzed using the alternating current impedance method for measurements over a wide frequency range. Each result had a different spectrum up to 1 kHz. In addition, we show the basic inside condition of EDLCs with equivalent circuit analysis. This paper explores the possibility of degradation diagnosis at a high frequency and the basic physical mechanism.