"Blue energy" from ion adsorption and electrode charging in sea- and river water

Niels Boon (1) , René Van Roij (1)

1 Institute for Theoretical Physics [Utrecht]

A huge amount of entropy is produced at places where fresh water and seawater mix, for example at river mouths. This mixing process is a potentially enormous source of sustainable energy, provided it is harnessed properly, for instance by a cyclic charging and discharging process of porous electrodes immersed in salt and fresh water, respectively [D. Brogioli, Phys. Rev. Lett. 103 , 058501 (2009)]. Here we employ a modified Poisson-Boltzmann free-energy density functional to calculate the ionic adsorption and desorption onto and from the charged electrodes, from which the electric work of a cycle is deduced. We propose optimal (most efficient) cycles for two given salt baths involving two canonical and two grand-canonical (dis)charging paths, in analogy to the well-known Carnot cycle for heat-to-work conversion from two heat baths involving two isothermal and two adiabatic paths. We also suggest a slightly modified cycle which can be applied in cases that the stream of fresh water is limited.

Mots clés: Physical Sciences

Domaines: Matière Condensée [cond-mat]

Niels Boon, René Van Roij. "Blue energy" from ion adsorption and electrode charging in sea- and river water. Molecular Physics, 2011, 109 (07-10), pp.1229-1241. ⟨10.1080/00268976.2011.554334⟩. ⟨hal-00692122⟩