Experimental Study on Ion Penetration into Pores with Pore Fractality at Carbon Electrode for EDLC

Abstract

Ion penetration into pores during double-layer charging/discharging has been investigated by analyses of potentiostatic current transients ͑PCTs͒ and cyclic voltammograms ͑CVs͒ experimentally measured on porous carbon electrodes with pore fractality. From the analyses of the cathodic PCTs measured on microporous electrodes, it was found that the PCTs showed ideal behavior with a slope of −0.5 in the earlier stage, indicating that the change in the resistance-capacitance ͑RC͒ time constant distribution produced by pore fractal dimension in the micropore size range is too small to affect the shape and value of the PCT. The cathodic PCTs measured on meso/macroporous electrodes exhibited anomalous behavior with a slope lower than −0.5 in the earlier stage due to the considerably wider RC time constant distribution. From the analyses of the cathodic PCTs measured on multifractal electrodes, it is strongly suggested that the current decays more rapidly with increasing relative volume fraction of larger-sized pores. From the analyses of the measured CVs, it is experimentally confirmed that the higher relative volume fraction of larger-sized pores enhances the rate capability ␥, which yields us the higher power density, but it reduces the double-layer capacitance, which provides us the lower energy density.

Charging dynamics of an individual nanopore

“…This is well understood for planar electrodes in bulk solution, where the characteristic charging time is defined by τ c = λ D H / Ɗ (where H is the distance between electrodes and Ɗ is the ion diffusion coefficient) 19 – 22 , but for the case of EDL charging in nano-confined geometries (as in porous electrodes) the dynamics may be much slower. This is because, in small diameter pores, changes to the EDL are constrained by the limited supply of ions within the pore 23 – 27 and the time for ions to access the entire pore from the reservoir with which it is in contact.…”

Theory of the Electrochemical Impedance of Mesostructured Electrodes Embedded with Heterogeneous Micropores

“…At low frequency, ω < ω H , the CPE behavior results from the heterogeneity in the surface of micropores unlike from distribution of penetration length or pore size. , We observed from the plots that the bimodal porous electrode embedded with cylindrical micropores with high surface heterogeneity characterized by low γ* value have slower interfacial EDL dynamics than lesser heterogeneous surface with higher value of γ*. The effect of heterogeneity is very strong in low frequency CPE regime which also indicates that the presence of such features will be important in charge storage in porous carbon supercapacitor. , Glassy carbon electrodes with edge and basal orientation have γ* in the range of 0.91 and 0.96 . This is also prominent in the phase plot (b), which shows lowering in value from ideal 90° to lesser values around 80° and 70° for highly heterogeneous surface with γ* as 0.9 and 0.8, respectively.…”

“…The effect of heterogeneity is very strong in low frequency CPE regime which also indicates that the presence of such features will be important in charge storage in porous carbon supercapacitor. 49,50 Glassy carbon electrodes with edge and basal orientation have γ* in the range of 0.91 and 0.96. 51 This is also prominent in the phase plot (b), which shows lowering in value from ideal 90°to lesser values around 80°and 70°for highly heterogeneous surface with γ* as 0.9 and 0.8, respectively.…”

A Porous Carbon Prepared by Using a Mordenite Mineral as Template and its Cyclic Voltammetry Study in H₂SO₄

“…However, when scan rates increased, ions moved very fast. Large pores are necessary to offer enough large channels for rapid motion of the ions [15,16]. The templated carbon in this paper thus has large capacity at higher scan rate.…”