Ambient-temperature molten salts of formula (I): wherein Y+ is a cation selected from the group consisting of an ammonium ion, a sulfonium ion, a pyridinium ion, a(n) (iso)thiazolium ion, and a(n) (iso)oxazolium ion that may be optionally substituted with C1-10 alkyl and/or C1-10 alkyl having ether linkage, provided that the above cation has at least one substituent of —CH2Rf1 or —OCH2Rf1 (wherein Rf1 is C1-10 perfluoroalkyl); Rf2 and Rf3 are independently C1-10 perfluoroalkyl or may together form C1-4 perfluoroalkylene; and X is —SO2— or —CO—.