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‘Blue energy’ from ion adsorption and electrode charging in sea and river water

2011; Taylor & Francis; Volume: 109; Issue: 7-10 Linguagem: Inglês

10.1080/00268976.2011.554334

1362-3028

Niels Boon, René van Roij,

Analytical Chemistry and Sensors

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. Keywords: blue energyPoisson–BoltzmannCarnot cycleporous electrodesosmotic power This article is part of the following collections: Longuet-Higgins Early Career Researcher Prize Acknowledgements It is a great pleasure to dedicate this paper to Bob Evans on the occasion of his 65th birthday. RvR had the privilege of being a postdoctoral fellow in Bob's group in the years 1997–1999 in Bristol, where he experienced an unsurpassed combination of warm hospitality, unlimited scientific freedom, and superb guidance on any aspect of scientific and (British) daily life. Bob's words ‘René, you look like a man who needs a beer!’ when entering the post-doc office in the late afternoon, which usually meant that he was ready to discuss physics after his long day of lecturing and administration, trigger memories of evening-long pub-discussions and actual pencil-and-paper calculations on hard-sphere demixing, like-charge attraction, liquid-crystal wetting, poles in the complex plane, or hydrophobic interactions, with (long) intermezzos of analyses of, say, Bergkamp's qualities versus those of Beckham. Even though not all of this ended up in publications, Bob's input, explanations, historic perspective, and style contained invaluable career-determining elements for a young postdoc working with him. RvR is very grateful for all this and more. We wish Bob, and of course also Margaret, many happy and healthy years to come. We thank Marleen Kooiman and Maarten Biesheuvel for useful discussions. This work was financially supported by an NWO-ECHO grant.