Thermally Regenerable Redox-Flow Batteries

A Thermally Regenerable redox-flow Batterie (TRB) is an electrochemical cell which produce electrical current by consuming solutions, with the same composition, but different concentrations. In this kind of device, the two solutions can be regenerated by distillation, exploiting low temperature heat (<100°C) produced in different industrial applications. The produced energy is extracted at the expenses of the mixing free energy of the two solutions. This cell stores energy in form of solutions and it will enable to convert heat from geothermal sources, industrial waste and solar heat collected by low-concentration optics, in a more efficient way then the traditional thermoelectrical converters. The efficiency of the whole device depends by the efficiency of the electrochemical cell and the efficiency of the distillation unit, which can be improved choosing a salt that gives a high boiling point elevation. An example of TRB is based on LiBr solutions, in which the different electrochemical equilibrium reached at the electrodes (Pt) lead to an efficient production of electrical current, with the passage of Li+ and production/consumption of Br2 and Br– at the electrodes. To equilibrate the bromine concentration (to extract the maximum energy possible), the solutions are pumped in a second device called “through liquid exchanger” which is based on the passage of bromine through an organic solvent in which LiBr and water are insoluble. A cell based on LiBr could provide 38,5 Wh/L starting from two solutions at 26% and 2.5% of molar fraction at room temperature.