Tetrakis(diethylamino)phosphonium tetrafluoroborate (TDENPBF₄), tetrakis(diethylamino)phosphonium hexafluorophosphate (TDENPPF₆), and tetrakis(dimethylamino)phosphonium tetrafluoroborate (TDMNPBF₄) in acetonitrile (AN) have been studied as electrical double-layer capacitor electrolytes in a two-electrode test cell using titanium carbide derived carbon, C(TiC), as an electrode material. Electrochemical characteristics for C(TiC)|1 M TDENPBF₄ + AN, C(TiC)|1 M TDENPPF₆ + AN, and C(TiC)|1 M TDMNPBF₄ + AN interfaces have been obtained by cyclic voltammetry, constant current charging/discharging, and electrochemical impedance spectroscopy. High-capacitance (85 °F/g) and gravimetric power (269 kW/kg) have been achieved at cell voltage 3.2 V. Data obtained have been compared with results published previously.