'Blue energy' from ion adsorption and electrode charging in sea and river water
Abstract
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.
- Publication:
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Molecular Physics
- Pub Date:
- March 2011
- DOI:
- 10.1080/00268976.2011.554334
- arXiv:
- arXiv:1012.4946
- Bibcode:
- 2011MolPh.109.1229B
- Keywords:
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- blue energy;
- Poisson-Boltzmann;
- Carnot cycle;
- porous electrodes;
- osmotic power;
- Condensed Matter - Statistical Mechanics
- E-Print:
- 7 Figures