Waste thermal energy, such as that released from industrial or manufacturing processes, is a promising but as-yet underutilized source of sustainable energy. As an alternative to traditional semi-conductor based thermoelectrics, thermoelectrochemical cells use a redox couple in an electrolyte to directly convert thermal energy to electricity using a very simple device design. The good thermal stability of many ionic liquids (ILs) makes them very promising electrolytes for these devices, but the influence of the nature of the cation and anion on the cell performance is not yet well understood. Here we report measurement of the Seebeck coefficient and the thermoelectrochemical device performance of a cobalt redox couple in a series of ILs, and comparison of the electrolyte performance using a modified figure of merit. (C) 2014 The Electrochemical Society. All rights reserved.