CMK-5-Based High Energy Density Electrical Double Layer Capacitor for AC Line Filtering

Abstract

Compact electrical double layer capacitors (EDLCs) can be applied to the AC line filtering process and potentially replace conventional bulky aluminum electrolytic capacitors. However, to realize the AC line filtering application, the energy density of the EDLCs needs to be significantly increased while high power density is maintained. In this work, we demonstrate the EDLCs fabricated with ordered mesoporous carbon, CMK-5, and small amounts of single walled carbon nanotubes (SWNTs), which exhibit the highest areal energy density among various EDLCs reported so far and power performance sufficient for AC line filtering. High energy density of CMK-5/SWNT EDLCs can be attributed to high capacitance arising from the bimodal mesoporosity of CMK-5 and high operation voltage owing to the pores compatible with ion sizes in organic electrolytes. High power density is ascribed to the high electrical conductivity and straight ordered pore structure of CMK-5, enabling facile ion movements. Therefore, the carbon pore structure is one of the critical factors to be controlled for the enhancement of the overall performance of EDLCs for AC line filtering. Our demonstration would greatly contribute to the scientific and technological advancement of AC line filtering EDLCs.

Nickel Alloying Significantly Enhances the Power Density of Ruthenium‐Based Supercapacitors

“…[27] A previous report suggests that RuO 2 can undergo a redox reaction in a nonacidic environment according to Equation (1): [40] Ru IV Figure 3F depicts the discharge peak current density as a function of the scan rate, showing a linear behavior nearly up to 2000 V s À 1 , which is higher than previously reported RuO 2 devices, [41] MXene devices [27,28] and carbon-based devices. [10,13,19] A high capacitance of 1.93 mF cm À 2 at 10 V s À 1 , 0.79 mF cm À 2 at 1000 V s À 1 (41 % retention), and 0.46 mF cm À 2 at 2000 V s À 1 (24 % retention), calculated from the CV curves ( Figure S9), far exceed corresponding values reported for other ultrahigh power supercapacitors. [13,19,27] The important contribution of the nickel constituent to the remarkable electrochemical performance of the NiRu/RuO 2 device (e. g. Figure 3), both as enhancer of the porous morphology and vehicle for greater conductivity, is further supported by the observation of a highly limited capacitive properties of a Ni-only device ( Figure S10).…”

“…[10,13,19] A high capacitance of 1.93 mF cm À 2 at 10 V s À 1 , 0.79 mF cm À 2 at 1000 V s À 1 (41 % retention), and 0.46 mF cm À 2 at 2000 V s À 1 (24 % retention), calculated from the CV curves ( Figure S9), far exceed corresponding values reported for other ultrahigh power supercapacitors. [13,19,27] The important contribution of the nickel constituent to the remarkable electrochemical performance of the NiRu/RuO 2 device (e. g. Figure 3), both as enhancer of the porous morphology and vehicle for greater conductivity, is further supported by the observation of a highly limited capacitive properties of a Ni-only device ( Figure S10). Figure 4 presents the frequency response of the symmetric NiRu/RuO 2 device, calculated through application of electro-chemical impedance spectroscopy.…”

“…Echoing the superior electrochemical properties highlighted in Figures 3 and 4A-B, the high capacitance at 120 Hz (1.31 mF cm À 2 ) outperforms devices fabricated by varied other methods, including vertically aligned graphene on cellulose fibers, [39] vertically aligned CNTs, [10] MXene, [27] and other carbonbased materials. [13,19,44] This result is likely due to the high surface area afforded by the NiRu nanostructures. From the calculated capacitance and resistance at 120 Hz, a very low RC time constant (τ RC ) of 0.31 ms was obtained.…”

“…[8] The resistance at 120 Hz of NiRu/RuO 2 device, extracted from the Nyquist plot in Figure 4A, is 0.260 Ω cm 2 , which is lower than previously reported planar devices comprising graphene, [16] carbon nanotubes, [10,31] and electrodeposited RuO 2 , [41] and comparable to mesoporous carbon devices fabricated on 3D templates. [13] The capacitive behavior of the NiRu/RuO 2 symmetric supercapacitor was further assessed by calculating the phase angle as a function of frequency ( Figure 4B, black circles). In such measurements, a phase angle of À 90 0 corresponds to ideal capacitive behavior, while a phase angle of 0 0 is indicative of a resistor.…”

“…[10] Motivated by these studies, research on SCs which can operate at high frequency/scan rates have mostly focused on devices based upon electric double-layer capacitor (EDLC) mechanisms. Materials such as onion-like carbon, [11] mesoporous carbon, [12][13][14] covalent organic frameworks, [15] and exfoliated graphene, [16] have been promoted as candidates for highfrequency EDLC-based supercapacitors. Yet, low material densities and reduced specific capacitance generally require high mass loading in such devices in order to achieve high capacitance.…”