The invention generally encompasses phosphonium ionic liquids and compositions and their use in many applications, including but not limited to: as electrolytes in electronic devices such as memory devices including static, permanent and dynamic random access memory, as battery electrolytes, as a heat transfer medium, fuel cells and electrochromatic devices, among other applications. In particular, the invention generally relates to phosphonium ionic liquids, compositions and molecules possessing structural features, wherein the molecules exhibit superior combination of thermodynamic stability, low volatility, wide liquidus range and ionic conductivity. The invention further encompasses methods of making such phosphonium ionic liquids, compositions and molecules, and operational devices and systems comprising the same.