Widening the limit of capacitance at high frequency for AC line-filtering applications using aqueous carbon-based supercapacitors

Portable electronic devices require high-performance miniaturised electronic components, preferably produced at low cost. In most line-powered applications, alternating current (AC) line filters are used to filter AC lines to direct current (DC) signals, making filtering capacitors a key necessity in modern electronic devices. Currently, aluminium electrolytic capacitors (AECs) are commonly used, which are bulky and have narrow electrochemical performance. Thus, replacing AECs with a compact capacitor design is highly desirable for future portable electronic devices but simultaneously very demanding. Here, we report the fabrication of an electrochemical capacitor with an electrode based on vertically aligned carbon nanostructures produced by a green plasma-enabled deposition technique. These capacitors delivered a high capacity of 1145 μF with a phase angle close to −80° at 100 Hz in a lab-scale two-electrode set-up. A prismatic prototype capacitor fabricated by stacking 10 pairs of electrodes (2.5 × 3.5 cm2) showed one of the lowest equivalent series resistance values, about 5.8 mΩ, with a high capacitance of ∼12 mF at 100 Hz. This performance delivered at the lab scale and in industrial-relevant environments suggests such electrochemical capacitors represent a suitable alternative to conventional AECs for high-frequency filtering applications.