Thermally Regenerable Redox Flow Battery

Abstract

The efficient production of energy from low-temperature heat sources (below 100°C) would open the doors to the exploitation of a huge amount of heat sources such as solar, geothermal, and industrial waste heat. Thermal regenerable redoxflow batteries (TRBs) are flow batteries that store energy in concentration cells that can be recharged by distillation at temperature < 100°C, exploiting low-temperature heat sources. Using a single membrane cell setup and a suitable redox couple (LiBr/Br 2), a TRB has been developed that is able to store a maximum volumetric energy of 25.5 Wh dm À 3 , which can be delivered at a power density of 8 W m À 2. After discharging 30 % of the volumetric energy, a total heat-to-electrical energy conversion efficiency of 4 % is calculated, the highest value reported so far in harvesting of low-temperature heat.

Thermally regenerative electrochemically cycled flow batteries with pH neutral electrolytes for harvesting low-grade heat

“…The scaled efficiency is 0.9% relative to the Carnot / limit. Figure 8b 24,53 thermally regenerative electrochemical cycles (TREC), [25][26][27] vacuum distillation -concentration redox flow battery (VD-CRFB), 21,22 vacuum distillation/membrane distillation -reverse electrodialysis (VD/MD-RED), 54,55 thermolysisreverse electrodialysis (TL-RED), 56 vacuum distillation/membrane distillation-pressure retarded osmosis (VD/MD-PRO), 57,58 thermo-osmosis energy conversion (TOEC), 59 thermally charged batteries including thermally regenerative ammonia battery (TRAB), [12][13][14][15][16][17][18][19] thermally regenerative copper acetonitrile battery (CuACN). 20 To provide insights for future improvement of power density and higher efficiency, it is important to understand the factors contributing to the overpotential as an irreversible loss.…”

“…(20) and the boundary conditions in Eq. (22). At each point along the flow direction, the overpotential profile as a function of is solved, and the final measured overpotential is taken as the ± averaged value of inside the electrode domain.…”

“…More recently, VD-CRFBs have been developed utilizing the concentration difference induced electromotive forces for energy conversion, with a vacuum distillation for regenerating the concentration difference. 21,22 VD-CRFBs also showed competitive power density and even higher efficiency than copper ammonia batteries. Thermogalvanic cells, on the other hand, generate electricity continuously as long as there is a temperature difference across the device.…”

“…This recent pursuit is because the "effective thermopower" (on the order of 1 to 10 mV/K) [2][3][4][5] is relatively high compared with thermoelectric materials (~ 200 μV/K). 6 Several different types of devices have been investigated, [7][8][9] including thermionic capacitors, 10,11 thermally charged batteries, [12][13][14][15][16][17][18][19][20] , vacuum distillation -concentration redox flow battery (VD-CRFB), 21,22 thermogalvanic cells, 23,24 thermally regenerative electrochemical cycles (TREC) [25][26][27] and thermally regenerative electrochemically cycled flow batteries (TREC-FB) 28,29 . Thermionic capacitors rely on the thermodiffusion of ions, also known as the Soret effect.…”

Thermo-Electrochemical Redox Flow Battery for Continuous Conversion of Low-Grade Waste Heat to Power

“…Newer heat-to-power technologies, e.g. Reverse Electrodialysis 4,5,6 , Thermal Regenerable redox-flow Batteries 7,8 or Pressure Retarded Osmosis combined with membrane distillation 9,10 , have not shown higher energy efficiencies. Hence, a heatto-power technology with potential for high energy efficiency is demanded.…”