8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P2.13“Blue energy” from ion adsorption and electrodecharging in sea- and river waterNiels Boon 1 and René van Roij 11 Utrecht University, Leuvenlaan 4, 3584CE, Utrecht, NetherlandsA huge amount of entropy is produced at places where fresh and salty water mix, for example atriver mouths. This mixing process involves a potentially enormous source of sustainable energy,the equivalent of a waterfall of 100-200m. The global potential of this energy source is of the orderof today’s global electricity consumption. Harnessing this so-called ”blue energy” is possible, forinstance by a cyclic charging and discharging process of porous electrodes immersed in salt andfresh water, respectively [D. Brogioli, Phys. Rev. Lett. 103, 058501 (2009)]. This prototype ”blueengine” involves aqueous electrolytes in contact with highly charged electrodes, double layers,ionic screening and effective RC times. We [1] propose optimal (most efficient) cycles for twogiven salt baths involving two canonical and two grand-canonical (dis)charging paths, in analogyto the well-known Carnot cycle for heat-to-work conversion from two heat baths involving twoisothermal and two adiabatic paths. We also suggest a slightly modified cycle which can beapplied in cases that the stream of fresh water is limited. Interestingly, the latter can also be usedin reverse-mode to desalinate water – at the expense of energy input not unlike a fridge. This workshows that liquid-state theory can directly contribute to the development of sustainable sources ofenergy and fresh water.[1] N. Boon and R. van Roij, Mol. Phys. 109 (2011) DOI: 10. 1080/00268976. 2011 55433413