Design and Demonstration of Concentration Cells for Small Scale Energy Harvesting based on Reverse Electrodialysis
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Design and Demonstration of Concentration Cells for Small Scale Energy Harvesting based on Reverse Electrodialysis Ramin Banan Sadeghian, Oxana Pantchenko, Daniel Scott Tate, Javad Shabani, Mehrdad M. Zarandi, and Ali Shakouri University of California – Santa Cruz, 1156 High St., Santa Cruz, CA 95064, U.S.A. ABSTRACT Experimental results are presented to demonstrate feasibility of small scale power generation using static reverse electrodialysis (RED) of CuSO4 solutions. In contrast to conventional macro scale reverse electrodialysis, the concentrated and diluate compartments were not refreshed, resulting in limited power delivery times. This is important in energy harvesting applications from limited supply of ionic concentrations. Maximum output power density of 0.17 W·cm-2 was recorded using microfiltration membranes. The evolution of the open circuit output voltage with time is accurately modeled at various concentration ratios. INTRODUCTION Miniaturized concentration cells have potential applications as in-vivo power sources for implantable bioelectronics such as sensors and diagnostic devices, as well as power supply in remote locations from limited amount of salt or ionic solutions. A concentration cell uses the Gibbs energy stored in two half-cells containing different concentration of a solute, separated by an ion-exchange membrane. Thus far, large scale concentration cells were designed to generate sustainable electricity from river water and seawater. To maintain a constant output power level the diluate (feed) and concentrated (brine) compartments must be constantly refreshed [1-2]. Modeling attempts so far have been focused on explaining the steady state output characteristics rather than on the decaying behavior of power level with time. In the present study, however, instantaneous output power levels of millimeter-size concentration cells were recorded until the cells were depleted. EXPERIMENTS AND THEORY Experimental details For experimental simplicity reasons we chose copper ribbons and cupric sulphate (CuSO4) solution as the electrodes and electrolyte respectively. Such a configuration belongs to the group of RED systems with opposite electrode reaction where there is no net chemical reaction [3]. Copper ribbons were cut out from adhesive copper tapes. CuSO4 solutions were prepared by dissolving CuSO4·5H2O powder, purchased from Fisher Scientific, in deionized water. The prototype was comprised of a concentration cell fabricated by cast-molding two identical PDMS slabs each having a compartment 5 mm in diameter and 7 mm in height. Each compartment served as a concentration half-cell. The semi-permeable microfiltration membrane, MF-MilliporeTM, was placed between the slabs before they were tightly bonded under pressure. MF-Millipore filters are made of biologically inert mixtures of cellulose acetate and cellulose nitrate and are ~105 μm thick. The half-cell located at one of the PDMS slabs was filled with a
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1.0 Mol·Litre-1 solution of CuSO4 while the half-cell at the other slab was filled wit
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