Boosting capacitive blue-energy and desalination devices with waste heat

TL;DR

This paper demonstrates that varying water temperature can significantly boost the efficiency of capacitive blue-energy and desalination devices, leveraging temperature-dependent electrostatic potentials to enhance energy output and water purification.

Contribution

It introduces a novel approach to enhance blue-energy harvesting and desalination by exploiting temperature dependence of electrostatic potentials in nanoporous supercapacitors.

Findings

Energy output can be doubled using waste heat from warm fresh water.

Temperature dependence of electrostatic potential is significant and exploitable.

The physics can optimize both energy harvesting and desalination processes.

Abstract

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