A kilohertz frequency response pseudocapacitor

Abstract

Electrochemical supercapacitors have orders of magnitude higher energy density than a dielectric/electrolytic capacitor (EC), but most are unsuitable for applications involving high-frequency signals since their capacitive behavior is limited by the high equivalent series resistance (ESR) to signals of frequencies below 5 Hz. The kHz frequency response supercapacitors are exclusively carbon electrode-based electric double layer capacitor (EDLC). However, an EDLC's areal capacitance is limited by the straight-channel porous morphology of the electrode required for low electrolyte resistance. Moreover, an EDLC's capacitance decays rapidly for frequencies beyond 10 kHz. A pseudocapacitor has a higher specific capacitance than an EDLC, but a kHz pseudocapacitor is not reported. Here we show a titania-based, kHz pseudocapacitor whose ability to retain capacitive behavior at high frequencies (190 μF cm−2 at self resonance frequency (SRF) of 51 kHz) is far superior to the kHz EDLCs (20 μF cm−2 at 80 kHz SRF or 67 μF cm−2 at 20 kHz SRF). The pseudocapacitor could filter a 50 kHz sinusoidal signal to a smooth line with a variance of less than 9×10−4. The variance of 7×10−4 for filtering a 60 Hz AC signal to a smooth line is considerably better than filtering by an EC.