Ionic liquids composed of a hydrophobic anion, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB-), and various aromatic and aliphatic ammonium have been prepared. TFPB salts of N-octadecylisoquinolinium (C(18)Iq(+)) and trioctylmethylammonium (TOMA(+)) show low melting points of 31 and 36 degrees C, respectively, whereas TFPB-based ionic liquids of 1-alkyl-3-methylimidazolium with the alkyl chain length of 5-12 show melting points lower than 90 degrees C. The [C(18)Iq][TFPB]vertical bar water (W) and [TOMA][TFPB]vertical bar W interfaces have the polarized potential window (ppw) of 0.8 V at 56 T, which is twice as wide as the ppw at the interface between W and room-temperature ionic liquids of bis(perfluoroalkylsulfonyl)imide so far reported. The extension of the ppw by more than 0.4 V to the positive direction enables voltammetric measurements of the ion transfer of relatively hydrophobic anions such as bis(trifluoromethylsulfonyl)imide and bis(pentafluoroethylsulfionyl)imide and of hydrophilic cations such as tetraethylammonium and acetylcholine ions.