Temperature Effects on Energy Production by Salinity Exchange

Abstract

2In recent years, the capacitance of the interface between charged electrodes and 3 ionic solutions (the electric double layer) has been investigated as a source of clean 4 energy. Charge is placed on the electrodes either by means of ion-exchange membranes 5 or of an external power source. In the latter method, net energy is produced by simple 6 solution exchange in open circuit, due to the associated decrease in the capacitance of 7 the electric double layer. In this work, we consider the change in capacitance associated 8 to temperature variations: the former decreases when temperature is raised, and hence, 9 a cycle is possible in which some charge is put on the electrode at a certain potential 10 and returned at a higher one. We demonstrate experimentally that it is thus viable 11 to obtain energy from electric double layers if these are successively contacted with 12 water at different temperatures. In addition, we show theoretically and experimentally 13 that temperature and salinity variations can be conveniently combined to maximize 14 the electrode potential increase. The resulting available energy is also estimated.

Heat-to-current conversion of low-grade heat from a thermocapacitive cycle by supercapacitors

“…The proposed engine effectively isolates the "thermal voltage rise" (TVR), introduced in earlier work to boost the work output of capacitive mixing engines [20,21]. Compared to a method which combines Capmix and a distiller [17], our thermocapacitive HTCC device has a less complex lay-out, since it consists solely of the supercapacitor.…”

“…The engines proposed in this study can work with (but are not restricted to) very low-temperature heat, which makes them especially interesting for the use of non-combustion waste heat of, for example, data centers, geothermal reservoirs, bio-mass heat or ocean thermal energy. Moreover, in our HTCC no solvents or electrolytes must be exchanged, as necessary in Capmix [21]. Instead, the whole sealed device at once is successively connected to heat reservoirs at different temperatures.…”

Microscopic insights into the efficiency of capacitive mixing process

“…There have been a number of experimental efforts to measure the energy output of CDLE processes . Most experimental works focus on the exploration of appropriate electrode materials.…”

Harvesting vibrational energy with liquid-bridged electrodes: thermodynamics in mechanically and electrically driven RC-circuits

“…The change in capacitance can be caused by a mechanical stimulus as in the case of vibrational-energy harvesters, but also by a change in the properties of the dielectric or electrolyte material. Examples of the latter include electrolyte-filled nanoporous supercapacitors where variable capacitance is achieved by changing electrolyte concentration (in capacitive mixing) [7,8], or temperature (in capacitive thermal energy extraction) [9], or combinations thereof [10,11].Variable-capacitance engines driven by mechanical energy typically consist of air-filled parallel-plate capacitors connected to a battery, where the capacitance is modified either by varying the plate separation or the lateral plate overlap [12]. A key new development in these engines was recently realized by Krupenkin and Taylor [4] who suggested to inject an array of small liquid droplets (Mercury and Galinstan) between the electrodes.…”

“…The change in capacitance can be caused by a mechanical stimulus as in the case of vibrational-energy harvesters, but also by a change in the properties of the dielectric or electrolyte material. Examples of the latter include electrolyte-filled nanoporous supercapacitors where variable capacitance is achieved by changing electrolyte concentration (in capacitive mixing) [7,8], or temperature (in capacitive thermal energy extraction) [9], or combinations thereof [10,11].…”