Aqueous high-energy-density capacitor with 2 V output voltage for alternating current line filtering

High-energy-density aqueous filtering capacitors are essential for the conversion of alternating current to direct current in contemporary integrated circuits. Yet their energy density is limited by the 1.23 V decomposition voltage of water. Here, we report an asymmetric electrolyte configuration to effectively suppress water decomposition activity, enabling the development of an aqueous filtering capacitor with a 2 V operating voltage, as well as an ultrahigh areal specific energy density of 4.51 ± 0.26 mF V 2  cm −2 (1.25 ± 0.07 μWh cm −2 ) at 120 Hz. This significant energy density value surpasses most reported filtering capacitors with a comparable phase angle of −(75.0 ± 1.0)° (Chi et al., 2017; Park et al., 2021; Zhang et al., 2022). Additionally, the capacitor presents outstanding cycling stability with a capacitance retention of 97.9 % after 200,000 cycles. Furthermore, we employ an alternatingly stacked assembly technique to conveniently construct compact and lossless integrated filtering capacitors, enabling efficient alternating current output smoothing from wind generator and ensuring stable power supply for light-controlled circuit. This work substantially advances line filtering electrochemical capacitors toward application in modern circuits.