Supercapacitors (SC) with kHz frequency response have been reported for about a decade as a promising replacement for the bulky aluminum electrolytic capacitors in AC line and other high-frequency signal filtering applications. Their adoption is primarily impeded by low voltage of operation, as the aqueous electrolyte constrains the cell voltage to approximately 1 V. This study demonstrates a kHz SC with operating voltage that is highest among aqueous electrolyte-based kHz SC reported for AC line filtering applications. The SC has reduced \(\textrm{TiO}_{2}\) nanotube array (R- \(\textrm{TiO}_{2}\) ) electrodes and uses 1 M \({\textrm{H}_{2}\textrm{SO}_{4}}\) electrolyte. The R- \(\textrm{TiO}_{2}\) nanotube electrode is synthesized by the anodization of a Ti sheet in an aqueous medium designed to obtain a precise control over the morphology. The R- \(\textrm{TiO}_{2}\) nanotube electrode demonstrates an impressive areal capacitance of 900 \(\mu\) F \(\hbox {cm}^{-2}\) , a phase angle of \(-82.6^{\circ }\) , and a characteristic frequency of 1.6 kHz. Additionally, it operates within a broad potential window of 2.3 V. The high areal capacitance and large voltage window lead to an impressive energy density (E \(\propto\) \(\hbox {V}^2\) ) of 0.33 \(\mu\) Wh \(\hbox {cm}^{-2}\) . The SC successfully filters 60 Hz AC signals (sine, ramp, and square waveforms) into a smooth DC output.
