BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:Harvesting "\;blue"\; energy from mixing river- and sea wa ter with supercapacitors - Professor Rene van Roij (Utrecht University) DTSTART:20141119T141500Z DTEND:20141119T151500Z UID:TALK55297@talks.cam.ac.uk CONTACT:Aron Cohen DESCRIPTION:Due to the irreversible mixing of fresh and salty water an eno rmous free-energy dissipation of about 2kJ per liter river water takes pla ce in river mouths\, equivalent to a waterfall of 200m. This source of ene rgy\, which is renewable and emission-free\, is currently untapped but cou ld globally account for several percent of the energy demand (and for much more locally in river deltas). Harvesting this so-called 'blue energy' h as become possible in recent years due to the development of nanostructure d devices\, either based on ion-selective membranes or on nanoporous solid -state electrodes that can form supercapacitors with internal surfaces of the order of a km2/kg. In this talk we will mostly focus on cyclic chargin g and discharging processes of these supercapacitors immersed in salty and fresh water\, respectively\, as constructed by Brogioli and coworkers [1\ ,2]. We will perform a thermodynamic analysis of this cycle\, mapping the ion flow and electric voltage-charge work of this 'blue engine' onto the h eat flow and the mechanical pressure-volume work of Stirling's heat engine [3]. Our mapping naturally leads to the prediction of the most efficient 'blue cycle' as an analogue of the Carnot cycle\, which harvests the full 2kJ/liter fully reversibly. Interestingly\, running the Carnot-like cycle backward is the basis for the thermodynamically cheapest desalination proc ess\, where brackish water is separated into fresh and salty water at the expense of a minimum energy input [3]. Microscopically\, on the nanometer scale\, these devices are governed by electric double layers at the electr ode-electrolyte interface\, where ionic packing\, hydration\, and polarisa tion affect the voltage-charge relation and the capacitance [4\,5]\, which we will briefly discuss. Finally\, we will focus on some recent and ongoi ng work on maximum power conditions (involving non-equilibrium (dis-)charg ing processes on the RC-time scale [6])\, temperature effects (involving c old sea water and warm fresh water for more efficient blue-energy harvesti ng using industrial waste-heat [7])\, and generalisations to run these dev ices on other chemical gradients (such as CO2 in clean air and in combusti on gases [8]). \n\n[1] D. Brogioli\, Phys. Rev. Lett. 103\, 058501 (2009). \n\n[2] D. Brogioli\, R. Zhao\, P.M. Biesheuvel\, Energy Environ. Sci. 4\, 772 (2011).\n\n[3] N. Boon and R. van Roij\, Mol. Phys. 109\, 1229 (2011) .\n\n[4] M.M. Hatlo\, R. van Roij\, and L. Lue\, Europhys. Lett. 97\, 2801 0 (2012). \n\n[5] R. van Roij\, in "Electrostatics of soft and disordered matter"\, Pan Stanford Publishing\, Singapore\, 2012\, eds D.S. Dean\, J. Dobnikar\, A. Naji\, and R. Podgornik\; cond-mat 1211.1269. \n\n[6] M. Kooiman\, master thesis\, Utrecht University (2012).\n\n[7] M. Janssen\, A. Härtel\, and R. van Roij\, cond-mat 1405.5830.\n\n[8] H.V.M. Hamelers et al.\, Environ. Sci. Tech. Lett. 1\, 31 (2014).\n LOCATION:Department of Chemistry\, Cambridge\, Pfizer lecture theatre END:VEVENT END:VCALENDAR