Advances in Science and Engineering for Brackish Water and Seawater Desalination II September 29 – October 3, 2013 Cetraro (CS), Italy Probing membranes and interfaces properties by impedance spectroscopy Enrica Fontananova 1 , Z. Wenjuan 1 , W. van Baak 2 , I. Nicotera 3 , C. Simari 3 , G. Di Profio 1 , E. Curcio 3 , E. Drioli 1,3 1 Institute on Membrane Technology (ITM – CNR), Rende (CS), Italy 2 Fujifilm Manufacturing Europe BV, Tilburg, The Netherlands 3 University of Calabria, Rende (CS), Italy
Salinity Gradient Power (SGP) is the energy available from the controlled mixing of two solutions with different salt concentrations. Pressure-retarded osmosis (PRO) and reverse electrodialysis (RE) are emerging as sustainable processes for capturing energy from saline solutions PRO RE Traditional approach: Diluate: fresh water Concentrate: seawater B. E. Logan, M. Elimelech, Membrane-based processes for sustainable power generation using water, Nature 488 (2012) 313-319
Reverse Electrodialysis Alternative Power production REAPOWER www.reapower.eu Project (n. 256736) The idea: • Power production through Salinity Gradient Power- Reverse Electrodialysis (SGP- RE) using brine as concentrated solution, and seawater as diluted solution. • To avoid the use of freshwater • Higher theoretical energy extractable Nernst potential: • Reduction of the internal electrical RT a resistance of the stack 0 c V ln theo zF a d
Reapower objectives: Create/select and optimise materials and components tailored to the requirements of New Ion Exchange the SGP-RE technology operating with high Membranes for highly salinity brine and seawater. These include the concentrated solutions membranes , spacers, electrodes and electrolytes Optimise the design of the SGP-RE cell pairs and High permselectivity stack using a computer modelling tool developed for that purpose Chemical and mechanical Verify the model, and assess the developed Stability materials, components and design through tests on laboratory stacks. Low electrical resistance Evaluate and improve the performance of the overall system through tests on a prototype fed with real brine from a salt pond Evaluate the results, analyze the economics and assess the perspectives of the technology www.reapower.eu
Membrane electrical resistance Ohm’s law With AC: impedance (Z) With DC: resitance (R) V V R ω = 2𝜌 Z ω I I ω Using an AC over a frequency range, it is possible to distinguish phenomena proceeding at different rates like bipolar concentration polarization E. Barsoukov, J. R. Macdonald, Impedance Spectroscopy. Theory, Experiment, and. Applications, Second Edition. John Wiley & Sons, New Jersey, 2005.
Electrochemical Impedance Spectroscopy (EIS) V ω Z ω I Z ω Z cos j Z sin ω V V sin t ω o Real part: Imaginary part: ( ω φ I I sin t ) ω o resistance reactance 𝑘 = −1
Concentration polarization: electrical double layer (EDL) and diffusion boundary layer (DBL) AEM CEM R edl R dbl + R edl R dbl - - - + + + - - + + - - + + - - + + - - + + - + - R tot = R m+s + R edl + R dbl At the interfaces between a solid ionic conductor and a liquid electrolyte, physical and electrical properties change suddenly because of an heterogeneous charges distribution (polarization) which reduce the overall electrical conductivity of the system.
The bipolar concentration polarization is time dependent and it undergoes an inversion during each AC cycle - + + + - CEM - + + + + - - + + + - + - + - - + [-] - - [+] - Catode + - + - + + Anode + [+] + + [-] - + - - + - + + + - - + + + + - - + DL SL SL DL DBL EDL EDL DBL
The bipolar concentration polarization is time dependent and it undergoes an inversion during each AC cycle + - + + - CEM - + + + + - - + + + - + - + - - + [+] [-] - - Anode + - + - + - + + Catode [-] + + - + - - + - [+] + + + - - + + + + - - + DL SL SL DL DBL EDL EDL DBL
Homogeneous reinforced IEM membrane Fuji-CEM-1 sdeveloped by Fujifilm Manufacturing Europe BV for SGP-RE Ion Density exchange Thickness Swelling of fixed Membrane capacity (µm)* (%)* charges (mmol/g (mol/L)* membrane) Fuji-AEM- 1.1 ± 0.1 166 ± 1 50.1 ± 2 2.2 ± 0.3 1 Fuji-AEM- 129 ± 2 1.4 ± 0.1 36.7 ± 0.04 3.8 ± 0.2 2 Fuji-AEM- 109 ± 2 1.6 ± 0.3 2.9 ± 0.6 53.1 ± 1.2 3 Fuji-CEM- 170 ± 1 1.6 ± 0.1 47.3 ± 0.8 3.4 ± 0.2 1 Fuji-CEM- 114 ± 2 1.1 ± 0.1 45.4 ± 0.4 2.4 ± 0.2 2 Fuji-CEM- 1.0 ± 0.3 113 ± 2 55.3 ± 0.2 1.8 ± 0.5 3 * NaCl 0.5M at 20 ° C E. Brauns Desalination 237 (2009) 378 – 391
Electrochemical Impedance Spectroscopy (EIS) 1000-0.01 Hz, signal amplitude of 10 mV • Solution velocity (1.5-4 cm s -1 ) • Solution concentration (0.5-4 M) • Temperature (20-40 ° C) E. Fontananova et al. submitted
Equivalent circuit model used to fit EIS spectra: R dbl R edl R m+s CPE dbl C edl Fuji-CEM-1 Fuji-AEM-1 Conditions: 1000-0.01 Hz; 0.5 M NaCl; 20 ° C; velocity 1,5 cm s -1 Good convergence of the fitting model with the experimental data
Effect of the velocity on the resistances 0.01 Hz 1.5 cm/s 2.8 cm/s 4 cm/s 1000 Hz Fuji CEM-1: 0.5 M NaCl; 20 ° C
Effect of the velocity on the resistances Fuji-AEM-1 R m > R dbl >R edl 0.5 3.0 Areal membrane resistance ( cm R dbl decreases with the 2 ) 2.5 0.4 Interfaces resiatance ( cm increasing of flow rate 2.0 0.3 R m R m and R edl are not 1.5 0.2 significantly influenced from R dbl 1.0 0.1 0.5 the flow rate R del 2 ) 0.0 0.0 1 2 3 4 -1 ) Velocity (cm s Fuji-AEM-2 Fuji-AEM-3 0.5 0.5 3.0 3.0 Areal membrane resistance ( cm Areal membrane resistance ( cm 2 ) 2 ) 2.5 2.5 0.4 0.4 Interfaces resistance ( cm Interfaces resistance ( cm 2.0 2.0 0.3 0.3 R m 1.5 1.5 0.2 0.2 R m 1.0 1.0 R dbl R dbl 0.1 0.1 0.5 0.5 R del R del 2 ) 2 ) 0.0 0.0 0.0 0.0 1 2 3 4 1 2 3 4 -1 ) -1 ) Velocity (cm s Velocity (cm s Conditions 0.5 M NaCl; 20 ° C
Effect of the velocity on the resistances R m > R dbl >R edl Fuji-CEM-1 0.5 R dbl decreases with the 3.0 R m Areal membrane resistance ( cm 2 ) Interfaces resistance ( cm 2.5 0.4 increasing of flow rate, but R dbl 2.0 also the R edl is influenced 0.3 R del 1.5 R m is not significantly 0.2 1.0 influenced from the flow 0.1 0.5 rate 2 ) 0.0 0.0 1 2 3 4 -1 ) Velocity (cm s Fuji-CEM-2 Fuji-CEM-3 0.5 0.5 3.0 3.0 R m Areal membrane resistance ( cm Areal membrane resistance ( 2 ) 2.5 2.5 0.4 0.4 Interfaces resistance ( cm 2 ) Interfaces resistance ( cm R dbl R dbl 2.0 2.0 0.3 0.3 R m 1.5 1.5 R del 0.2 0.2 1.0 1.0 R del 0.1 0.1 0.5 0.5 cm 2 ) 2 ) 0.0 0.0 0.0 0.0 1 2 3 4 1 2 3 4 5 -1 ) -1 ) Velocity (cm s Velocity (cm s Conditions 0.5 M NaCl; 20 ° C
R dbl AMR R edl AEMs have lower ( Ω cm 2 ) Membrane ( Ω cm 2 ) ( Ω cm 2 ) resistances than Fuji-AEM-1 1.63 0.0259 0.0860 CEMs Fuji-AEM-2 1.55 0.0135 0.0667 Ion Mobility Fuji-AEM-3 1.12 0.0184 0.0562 u (10 -8 m 2 V -1 s -1 ) Fuji-CEM-1 2.63 0.362 0.107 4.98 ± 0.19 Na + Fuji-CEM-2 2.96 0.0759 0.299 6.88 ± 0.31 Cl - Fuji-CEM-3 1.65 0.149 0.146 Data from S. Koneshan et al. J. Phys. Chem. B 1998, 102, 4193-4204 NaCl 0.5M; 20 ° C; 2.75 cm s -1 PS between concentrated solution Apparent Permselectivity (PS) (0.5M/4M NaCl) is above the between 0.05M/0.5 M NaCl*: threshold of 60% for*: > 90% for all samples Fuji-AEM-2: 65% Fuji-CEM-2: 84% *M. Papapetrou 4th International Conference on Ocean Energy, 17 October 2012, Dublin
Effect of the temperature on the resistances Fuji-CEM-2 Fuji-AEM-2 0.5 0.5 3.0 3.0 Areal membrane resistance ( Areal membrane resistance ( 2.5 0.4 2.5 0.4 2 ) 2 ) Interfaces resistance ( cm Interfaces resistance ( cm 2.0 2.0 R dbl 0.3 R m 0.3 1.5 1.5 0.2 0.2 R m 1.0 1.0 R del 0.1 R dbl 0.1 0.5 cm 0.5 cm R del 2 ) 2 ) 0.0 0.0 0.0 0.0 20 30 40 20 30 40 NaCl 0.5 M; 2.75 cm s -1 Temperature (°C) Temperature (°C) The resistance of the ion transport through the membrane, as well as through the interfaces, decreases with the temperature, because of the increasing ion mobility
Effect of the increasing solution concentration: test with 4 M NaCl (A) (B) Fuji-CEM-2; NaCl 4 M; 20 ° C; 1.5 cm s -1 In the case of the EIS experiments with 4 M NaCl solution, the fitting with the equivalent circuit (A) does not converge for most of the experiments. Only in few cases , the model converges but it gives a R edl values very low ( m Ω ) or negative, and the estimated error for R edl is high (> 100%). The data are successfully fitted with the equivalent circuit (B) reaching the convergence and a low estimated error (< 10 %)
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