We show that sustainably harvesting 'blue' energy from the spontaneous mixingprocess of fresh and salty water can be boosted by varying the watertemperature during a capacitive mixing process. Our modified Poisson-Boltzmanncalculations predict a strong temperature dependence of the electrostaticpotential of a charged electrode in contact with an adjacent aqueous 1:1electrolyte. We propose to exploit this dependence to boost the efficiency ofcapacitive blue engines, which are based on cyclically charging and dischargingnanoporous supercapacitors immersed in salty and fresh water, respectively [D.Brogioli, Phys. Rev. Lett. 103, 058501 (2009)]. We show that the energy outputof blue engines can be increased by a factor of order two if warm(waste-heated) fresh water is mixed with cold sea water. Moreover, theunderlying physics can also be used to optimize the reverse process ofcapacitive desalination of water.
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