Desalination 285 (2012) 147–152

Contents lists available at SciVerse ScienceDirect

Desalination

j ourna l homepage: www.e lsev ie r .com/ locate /desa l

Improved electrode systems for reverse electro-dialysis and electro-dialysis

Odne S. Burheim a, Frode Seland b, Jon G. Pharoah c, Signe Kjelstrup d,⁎a Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway and Wetsus, P.O. Box 1113, 8900 CC Leeuwarden, The Netherlandsb Department of Material Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norwayc Fuel Cell Research Centre, Queen's University, Kingston ON, Canada K7L 3N6d Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway

⁎ Corresponding author.E-mail address: signe.kjelstrup@chem.ntnu.no (S. Kj

0011-9164/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.desal.2011.09.048

a b s t r a c t

a r t i c l e i n f o

Article history:Received 2 March 2011Received in revised form 20 September 2011Accepted 29 September 2011Available online 27 October 2011

Keywords:Reverse electro-dialysisElectro-dialysisCarbon electrodesNoble metal oxide electrodes

Reverse Electro-Dialysis, RED, is an electrochemical technique to extract work by mixing aqueous solutions ofdifferent salinities. Electro-Dialysis, ED, is an electrochemical technique to extract potable water from seawa-ter. Both RED and ED typically employs noble metal oxide catalysts in the conversion between electroniccurrent and ionic current. By testing several different electrode materials and red-ox salts, this paper demon-strates that these electrochemical reactions are controlled by mass transfer in the electrolyte rather than bythe electrocatalytic properties of the electrode material. By comparing two different carbon materials andstandard noble metal oxides, we show, for two red-ox salts, that the electrochemical performances of the in-expensive and expensive materials are similar. Relatively inexpensive graphite along with environmentallybenign FeCl2 and FeCl3 in moderate concentrations was demonstrated to lower the electrode concentrationoverpotential.

elstrup).

rights reserved.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Chemical energy is continuously being dissipated as rivers world-wide mix with the ocean. The potential work, as 1 m3 of river watermixes with 1 m3 of sea water is of the order 2 MJ [1]. There are severalways to harvest this work, though in recent literature, the three mostfrequently discussed processes are; Pressure Retarded Osmosis (PRO)[2,3], Porous Capacitive Electrodes (PCE) [4-6] and Reverse Electro-Dialysis (RED) [1,7,8]. The three techniques may be subdivided intotwo categories, where RED and PCE are electrochemical processes(ionic selective membranes and electrodes for electricity production)and PRO is a mechanical process (water selective membranes andturbines for electricity production).

The main subject of this paper is RED as an electrochemical powersource, with focus on the electric power of a single cell. Realistic elec-trodes and electrode overpotentials will be studied.

The renewable power techniques all stem from their reversed de-salination technologies. Thus Electro-Dialysis (ED) indirectly becomesa present subject when RED is of interest. ED was introduced for com-mercial use in the 1960s to obtain potable water, about ten years be-fore Reverse Osmosis (RO) [9,10].

Since first reported by R.E. Pattle in the 50's [1], the idea of RED(and PRO) was left until the seventies when Weinstein [7] and Lacey[8], due to membrane development and a temporarily scarcity of oil

in the world market, took a renewed interest in this technology.Lacey performed a thorough evaluation of the economic and engineer-ing aspects of RED [8]. At the time it was found to be too expensive tobuild a commercial RED power system. During the last ten years, how-ever, the prices of membrane materials have dropped considerably (afactor of ten), and plans have been put forward for a commercial andeconomically viable plant within the next five years [11].

In general and over the most recent years, several aspects related toRED technology have been investigated. In particular, we have seen in-creased activity to find data related to membrane selectivity and resis-tance [12-14], to study the impacts of different spacers [15,16], toscale up stacks to give more power [17] and examine why RED has ahigh potential for harvesting power (electric work) from the mixingof sea and river water [18].

As with RED, the ED technique has received little attention when itcomes to optimisation of the electrode systems. This was reviewedand discussed by Veerman et al. [19]. Ag/AgCl-electrodes [20], Pt orRuO2 coated Ti anodes and stainless steel cathodes [21-24] havebeen deployed. In models, the concentration polarisation is only men-tioned briefly, e.g. [25]. Most ED units use water electrolysis, a highlyinefficient use of electric power [26,27]. The ED process can affordgreater dissipation of energy than RED, because its main objective ispotable water production, while RED has a limited potential energyto extract. The present work is motivated by an aim to aid cost reduc-tions for ED as well as RED, though it is the RED performance enhance-ment that is the main objective.

When scaling up small stacks to a large power plant, it is importantto deal with all types of dissipated energy (lost power or lost exergy)

148 O.S. Burheim et al. / Desalination 285 (2012) 147–152

in the cell. In this work, however, we focus on the energy dissipationrepresented by the electrode overpotential for active red-ox coupleand electrode reactions applicable in RED and ED. In practice, two sys-tems are of interest. The first has several small stacks, the advantagebeing that one unit can be replaced while the others are still running.The second has one large stack, the advantage being that few elec-trodes represent a relatively small loss [17]. This aim of this paper isto contribute to increasing the work output, especially in the first sys-tem, by reporting how power losses at the electrodes can be reducedduring operation by simple means. In the search for inexpensive, du-rable and electronically conducting materials, carbon materials arecentral, and we shall compare some types to highly active, noblemetal oxide electrode materials as well the effect of the concentrationof electroactive species.

We start by giving a short survey of the theoretical background(Section 2) before we present the experiments (Section 3), resultsand discussion (Section 4).

2. Electrochemical relations

After a presentation of an electrochemical system that is applicableboth for RED power production (and ED desalination), we give anoverview of the phenomena that are relevant for power losses in theelectrodes system.

2.1. The RED (and ED) system

The system in the present study uses the iron (II)/iron (III) red-oxcouple for the electrochemical conversion. At the anode, we have ox-idation of iron (II) Fe2+→Fe3++e− while reduction of iron(III)takes place at the cathode; Fe3++e−→Fe2+. The red-ox couple canbe added via different salts, e.g. K3Fe(CN)6/K2Fe(CN)6 or FeCl2/FeCl3.

The reverse electrodialysis stack can be described as follows;

AjFe2þ aqð Þ; Fe3þ aqð Þ;NaCl 1Mð ÞjjASM…… NaCl cCð Þ½ j CSMNaCl cDð Þj j ASMj � � N…

…Fe2þ aqð Þ; Fe3þ aqð Þ;NaCl 1Mð ÞjC ð1Þ

A range of materials can serve as anode or cathode, A and C, re-spectively, and N represents the number of repeating unit cells inthe stack. The repeating unit consists of a concentrated saline solutioncC, a Cationic Selective Membrane (CSM), a dilute saline solution cDand an Anionic Selective Membrane (ASM). The saline solutions in alaboratory are typically NaCl solutions, though for a real system seaand river water will be used. Sea water contains additional ionssuch as Mg2+, Ca2+, K+ and SO4

2− which hinder the performanceof the RED (and ED) unit, though monovalent ion selective mem-branes have been demonstrated to lower these effects [28].

The cell potential is proportional to the number of unit cells, N.The following effects reduce the cell potential and increase the dissi-pation of power in a RED (and ED) electrode surface; i) activationoverpotential, ii)concentration overpotential, iii) resistance towardselectron transport in the electronic conductors, and resistance to-wards ion transport in the electrolyte. We shall only be concernedwith the first two. A short description is given; for details we referto e.g. Newman [29].

2.2. Activation overpotential

At potentials close to the equilibrium value, the current density issmall, and the electrode overpotential is determined by the electrode–electrolyte interface and its ability to transport electrons between theelectrode and the active red-ox species. The relation between current

density and potential can be expressed by the well-known Butler–Volmer equation:

j ¼ j0 exp1−αð ÞnF

RTηs

� �−exp

αnFRT

ηs

� �� �ð2Þ

α,n,F,R and T are the transfer coefficient, mole electrons transferred inthe reaction, Faraday's constant, the universal gas constant, and thetemperature in Kelvin, respectively, while ηs, j0 and j are the surfaceoverpotential (or activation overpotential at the electrode), the ex-change current density and the net current density. At electrochemicalequilibrium, the anodic and cathodic partial current densities at theelectrode are equal, giving the exchange current density. An active in-terface gives a high exchange current density, normally implying asmall activation overpotential.

The Butler–Volmer equation can be simplified at high overpoten-tials, as one of the terms can be neglected. The resulting equation isthe renowned Tafel equation, which yields a straight line in an E-logjdiagram, Eq. (3). The charge transfer coefficient α depends on the ma-terial. It expresses howmuch the activation energy barrier will changeupon application of a potential.

ηa ¼ ln10RT

1−αð ÞnF logjj0

� �and ηc ¼ − ln10

RTαnF

logjj0

� �ð3Þ

The Tafel slope depends on the reaction mechanism, temperatureand symmetry coefficient. For simple one-electron transfer, we have;

ηα¼12;n¼1;T¼293K ¼ �0:116 log

jj0

� �ð4Þ

2.3. Concentration overpotential

While the activation overpotential dictates the current-overpotentialrelation at low tomoderate current densities, the concentration overpo-tential, ηcons, arises at large current densities. It is due to limitations inmass transfer of reactant and/or products to and/or from the electrodesurface. Mass transfer limitations occur when the flux of the electroac-tive components is insufficient to keep up with the changes at the sur-face, hence lowering the surface concentration of the reactant andincreasing the concentration of the product. This then leads to a reduc-tion in the reversible potential from the bulk phase and across the diffu-sion region towards the electrode surface and eventually to a masstransfer limited current density, jlim.

Across the diffusion layer, of thickness δd, concentration gradientsof the electroactive species arise. For the interdiffusion flux, J, of Fe2+

and Fe3+, we have

J ¼ −Ddcrdx

−dcpdx

� �ð5Þ

Here D is the interdiffusion coefficient, and j=FJ. A thinner diffu-sion layer, improves the flux of the active species, J, and increases j.

It follows that the concentration overpotential, in the presence ofNaCl as supporting electrolyte, becomes

ηcons ¼RTF

lncp;scr;bcp;bcr;s

!ð6Þ

where subscript r and p are reactants and products, respectively, sstands for the surface as before, and b is for the bulk solution outsidethe diffusion layer.

One way of reducing the mass transport limitations would be toagitate the electrolyte, either by a rotating disk electrode forming acontrolled, well-defined transport regime, by inert gas purging or by

149O.S. Burheim et al. / Desalination 285 (2012) 147–152

a magnetic stirrer. In practice, the simplest way is by forced convec-tion of the electrolyte, improving the transport properties of the elec-trolyte and its components, or simply by increasing the concentrationsof electroactive species.

3. Experimental

3.1. Cell setup

A three-electrode setup was used in the experimental investiga-tion of the electrode performance, see Fig. 1. The set-up consisted oftwo glass containers. The large glass (⊘=130 mm) was used as theelectrochemical cell while the small one (⊘=110 mm) was used asthe reference electrode compartment, accommodating a saturatedcalomel electrode in saturated potassium chloride, KCl(sat). The con-tainers were connected via a salt bridge containing Agar Gel with 1 MKCl. The salt bridge is made such that the tip can be placed rightunder or next to the working electrode area.

The working electrode consisted of pieces of materials cut to fitinto a custom made sample holder. In Fig. 1 the holder is sketchedand the black circle on the front of it shows the electrode material ex-posed to the electrolyte. The face of the electrode is 13 mm in diame-ter and is facing a Pt foil (11×11 mm2), sealed in glass, functioning asthe counter electrode. The face of the working electrode is sunk 4 mmfrom the edge of the sample holder. Considering this gap and the tip ofthe Agar Gel salt bridge being conical, the reference potential is 6–8 mm away from the electrode surface. The main advantage of theelectrode holder employed here is the simple replacement of workingelectrode material.

Fig. 1. The experimental setup for the electrode test rig using three electrodes. The ref-erence electrode is kept in a separate glass container and connected to the two otherelectrodes via an agar gel salt bridge. Convection in the cell is provided via a rotatingmagnet in the bottom of the main container.

Convection in the cell was provided from a magnetic stirrer and amagnet (l×⊘=60×9 mm) in the bottom of the large beaker.1 Nitro-gen, industrial quality 2.5, was continuously purged to remove dis-solved oxygen in the large beaker. A custom made lid of Teflon wasput on the top to seal the cell (not shown in the Figure).

3.2. Materials

Four different electrode materials were applied as working elec-trodes; PSC 101, PSC120, graphite and glassy carbon. The PSC mate-rials are DSA (Dimensional Stable Anode) materials supplied byPermascand AB. These materials consist of titanium support withnoble metal coatings designed to catalyse electrochemical reactionsin aqueous systems (e.g. the chlorine evolution in the chloralkali pro-cess and nickel electrowinning) and are thus promising electrodematerials also for RED (and ED). Graphite is a cheap material that en-compasses high electric conductivity and is used as the electrode ma-terial in many electrochemical processes. Glassy carbon has poorelectrocatalytic properties, but is more durable than graphite withimproved resistance towards erosion and electrochemical wear.Glassy carbon is sometimes used as a catalyst substrate [30,31] dueto its inert properties, i.e. solely and weakly capacitive within therange of 0–1.2 VRHE [32], and is thus taken into this study.

The electrolytes all contained 1 M NaCl together with either K4Fe(CN)6 and K3Fe(CN)6 or FeCl2 and FeCl3 as a red-ox couple. The con-centration of each iron oxide complex in the red-ox couples was either0.05 Mor 0.5 M, i.e. the total red-ox solution concentration 0.1 or 1 M.

3.3. Measurement procedure

An electrode pair and electrolytewere selected, and potentiodynamicsweeps at ±1 mV s−1 were conducted, starting from open circuit po-tential. This was done for each stirring rate, 0, 200, 300 and 400 rpm. Inone experiment the maximal stable stirring was applied, 700 rpm. Thethree electrode setup was controlled by a PC interfaced PAR 263 A/94(Princeton Applied Research) potentiostat (using the CorrWare PC soft-ware). The measurements yielded the relation between applied poten-tial and electric current.

The carbon materials were studied using the more common K4Fe(CN)6/K3Fe(CN)6 redox couple as a reference and these results werethen compared to the FeCl2/FeCl3 redox couple.

4. Results and discussion

In Section 1, we present results from kinetic studies of different elec-trode materials. Next, in Section 2, we compare two different red-oxcouples, while, in Section 3, a possible power gain is demonstrated.

4.1. Electrode materials

A sample group of four different materials were exposed to theferro cyanide solutions in the experimental setup depicted in Fig. 1.PSC101 and PSC120 are materials developed for anodes in aqueouselectrolysis and may thus be expected to have kinetics superior tothose of the graphite and the glassy carbon.

The results of the potentiodynamic sweeps at 1 mV s−1 of the per-formance of the two materials, PSC101 and glassy carbon, in the pres-ence of K4Fe(CN)6(aq)/K3Fe(CN)6(aq) and 1 M NaClaq at 298 K areshown in Fig. 2 at different stirring rates. The two other materialsgave the same results and are not shown.

For a simple one-electron transfer reaction, a Tafel slope of about±116 mV decade−1 is expected, cf. Eq. 4. We therefore adjusted thetwo lines of Eq. 4 to the E vs.log(j)-diagrams of Fig. 2 in such a manner

1 When it is later referred to stirring rates in the experiments it is the rate of thismagnet that is reported while the electrode and its holder is kept still.

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

log j / A cm-2

E v

s E

sce

/ VE

vs

Esc

e / V

log j / A cm-2

Fig. 2. Potentiodynamic sweeps, 1 mV s−1, of a DSA based electrode material and glass-y carbon electrode in 1 M NaCl, 0.05 M K4Fe(CN)6 and 0.05 M K3Fe(CN)6 at 298 K andat different stirring rates. The stippled lines give the Tafel behavior from Eq. 3. Theupper and the lower figures show results where PSC101 and glassy carbon were inves-tigated, respectively.

Table 2Results for the two red-ox couples of Fig. 3 using Eq. (4).

Red-ox couple Erev/V (vs. SCE) j0 and jlim/10−3Acm−2

K4Fe(CN)6/K3Fe(CN)6 0.24 1.1 and 6.5FeCl2/FeCl3 0.46 0.4 and 2.5

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.60

0.65

0.55

0.50

0.45

0.60

0.65

0.55

0.50

0.45

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

log j / A cm-2

E v

s E

sce

/ VE

sce

/ V

150 O.S. Burheim et al. / Desalination 285 (2012) 147–152

that they cross each other at the constant potential value when j→0.From this crossing we were able to find a rough estimate of theexchange current density, j0, of the different electrode materials.Table 1 gives the exchange current densities of the four investigatedcarbon materials.

Fig. 2 shows that the potential-current relationship depends onthe stirring rate. Considering the dependency of the limiting currentdensities, jlim on the stirring rate, the short range of contact betweenthe sweep lines and the Tafel lines, and that all materials investigatedgive the same exchange current densities, j0, it is fair to argue that theelectrochemical reactions are fast at all materials investigated here,and that all four systems are strongly dominated by mass transferphenomena, with a corresponding overpotential ηconc.

The fact that the investigated materials showed the same behavioris reassuring for at least two reasons. It shows not only that the cellgives reproducible results, but also that the electrode performance issolely related to having a conductive surface. The fact that the results

Table 1Exchange current densities determined from Fig. 2, and from the assumptionthat Eq. (4) applies to all electrode materials.

Electrode material j0/10−3Acm−2

(estimated from Eq. (4))

PSC101 1.1PSC120 1.1Polished graphite 1.1Glassy carbon 1.1

from the PSC101, a commercial material for the chloralkali industrywith expensive noblemetal coatings, is the same as that for glassy car-bon, a material which is known to be fairly electrochemically inactiveand also used as electrode backing material or catalyst carrier (for itsimpaired kinetics) [30,31], demonstrates that the most widely usediron based red-ox couple on a laboratory scale, has a performancethat depends exclusively on the concentration of the couple. Thus,an inexpensive and durable graphite material is an ideal choice forRED end compartment electrodes (Table 1).

4.2. The red-ox couple

The use of potassium iron cyanidesmay be harmful to the environ-ment, and poses a risk in case of ruptures of membranes adjacent tothe electrode compartments. An alternative which is more environ-mentally benign is the use of ferrous and ferric chlorides (FeCl2/FeCl3, respectively).

Potential sweeps for 0.05 M of the Fe (II)/Fe (III) red-ox couples in1 M NaCl are shown in Fig. 3 using the PSC101 electrode material. Re-sults for the potassium ferrocyanide couple are also shown for com-parison. One can see that the potassium iron-cyanide gives twice thevalue of the iron-chloride solutions in terms of current density. Thelimiting current density and the exchange current density are of the

0.40

0.35

0.30

0.25

0.40

0.35

0.30

0.251.E-05 1.E-04 1.E-03 1.E-02 1.E-01

log j / A cm-2

E v

s

Fig. 3. Potentiodynamic sweeps, 1 mv s−1 on a PSC101 electrode in 1 M NaCl and0.05 M K4Fe(CN)6/K3Fe(CN)6 (upper part) or 0.05 M FeCl2/FeCl3 (lower part).

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

log j / A cm-2

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

log j / A cm-2

E v

s E

sce

/ V

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

E v

s E

sce

/ V

Fig. 4. Potentiodynamic sweeps, 1 mV s−1, of a PSC101 electrode at 298 K and differentstirring rates. The dashed lines represent the calculated Tafel behavior from Eq. 3. Theelectrolytes used for the upper and the lower figures contained 0.5 and 0.05 M K4Fe(CN)6and K3Fe(CN)6, respectively, in addition to 1 M NaCl.

Fig. 5. Electrode overpotential (grey) and power loss (black) as functions of currentdensity for 0.05 M (left) and 0.5 M (right) K4Fe(CN)6 and K3Fe(CN)6. The possiblepower gain for two RED electrodes induced by increasing the concentration of the re-active components by a factor ten is shown as an insert in the lower right corner.

151O.S. Burheim et al. / Desalination 285 (2012) 147–152

same order of magnitude, however (Table 2). Tabulated values forthe electrode potential of the two red-ox couples differ [33].Versus a saturated calomel electrode, EFe3+/Fe2+

o =0.50 V andEo

Fe CNð Þ6½ �3−= Fe CNð Þ6½ �4− ¼ 0:12V. This is of less significance for the elec-

trodialysis cell, as the anode and cathode electrode reversible po-tentials cancel each other.

4.3. Reducing the power losses in the electrode compartments

In Fig. 4 and Table 3 the same type of results are reported forPSC101 and K4FeðCNÞ6ðaqÞ=K3FeðCNÞ6ðaqÞ, with a ten times higherconcentration of the red-ox couple.

The figure shows that the exchange current density increases as theconcentration of the red-ox couple increases. This is expected from atheoretical point of view, as the exchange current density is proportion-al to the square root of surface concentration of the reactant, j0∝cs

0.5

(considering a charge transfer coefficient of 0.5). The power lossesreported in Sections 1 and 2, i.e. the dissipated energy in the electrodecompartments, can thus be reduced by simply increasing the concentra-tion of the electroactive species, here K4FeðCNÞ6ðaqÞ=K3FeðCNÞ6ðaqÞ.

Table 3Exchange current densities determined graphically from the results in Fig. 4 and Eq. (4).

cK4Fe(CN)6/cK3Fe(CN)6

and a PSC101-electrodej0(estimated from Eq. 4)

jlim/10−3Acm−2

0.05 M 1.1 6-70.5 M 2.3 15

In Fig. 5, we give the overpotential (η – gray – left axis) and thecorresponding power loss (P=η⋅ j – black – right axis) as a functionof the current density. The inset in Fig. 5, gives the reduction of thepower loss from increasing the concentration of K4FeðCNÞ6 andK3FeðCNÞ6 from 0.05 M to 0.5 M times a factor two (because thereare two electrodes in the stack). This was found after doing a secondorder polynomial regression of the data.

These results mean that an increase in the concentration of theelectroactive species, not only can help increase the peak power of aRED cell, but it will also allow for a higher peak in the current densitycompared to what has previously been reported [17]. There is proba-bly an upper limit for how high the concentration can be. A saturatedsolution with reactants, (2–5 M) has a too high viscosity, meaningthat it becomes difficult to modify the diffusion layer thickness byforced convection. This is why the effect of the stirring becomes lessprominent with increasing concentration.

In order to reduce this type of power losses further, the activecross-sectional area must be increased. This can be done on themacro scale by creating a serpentine flow channel pattern in the elec-trode compartment in combination with a permeate spacers. This willincrease the cross-sectional area of the diffusion layer, thereby in-creasing reactant and product fluxes. The active surface area of theelectrode can also be increased, by increasing the porosity of the elec-trodematerial, although this is only significant if the electrode kineticsare limiting, cf Eqs. (2) and (3).

5. Conclusions

Reverse Electro-Dialysis, RED, has the potential become an impor-tant renewable power source. Electro-Dialysis, ED, has been demon-strated to be an important process for potable water. In both cases,however, the electrodes have received little attention. In this paperwe demonstrate that the most important source of dissipated energyin the electrode compartments, even at these low current densities,is due to mass transport of red-ox species. Simply by increasing theconcentration of the electro-active species somewhat, we documenthigher currents and higher power output in other investigated REDand ED systems, respectively.

We demonstrated that carbon, a cheap, electrically conductivema-terial, together with FeCl2/FeCl3 can function as electrodes in a red-oxsystem that converts the Gibbs energy of mixing or separating of seaand river water into electric power.

152 O.S. Burheim et al. / Desalination 285 (2012) 147–152

Acknowledgement

Permascand is acknowledged for supplying commercial electrodematerials. TheNorwegianUniversity of Science and Technology, Queen'sUniversity and theNorwegian Research Council is acknowledged for thefinancial support, Grant number 197598.

References

[1] R.E. Pattle, Production of electric power by mixing fresh and salt water in the hy-droelectric pile, Nature 174 (1954) 660.

[2] Gerstandt Karen, K.V. Peinemanna, Skilhagen Stein Erik, Thorsen Thor, Holt Torleif,Membrane processes in energy supply for an osmotic power plant, J. Desalination224 (2007) 64–70.

[3] Thorsen Thor, Holt Torleif, The potential for power production from salinity gra-dients by pressure retarded osmosis, J. Membr. Sci. 335 (2009) 103–110.

[4] D. Brogioli, Extracting renewable energy from a salinity difference using a capac-itor, Phys. Rev. Lett. 103 (2009) 058501–1 058501–4.

[5] B.B. Sales, M. Saakes, J.W. Post, C.J.N. Buisman, P.M. Biesheuvel, H.V.M. Hamelers,Direct power production from a water salinity difference in a membrane-modi-fied supercapacitor flow cell, Environ. Sci. Technol. 44 (2010) 5661–5665.

[6] D. Brogioli, R. Zhao, P.M. Biesheuvel, A prototype cell for extracting energy from awater salinity difference by means of dounle layer expansion of double layer innanoporous carbon electrodes, Energy Environ. Sci. 4 (2011) 772–777.

[7] J.N. Weinstein, F.B. Leitz, Electric power from differences in salinity: the dialyticbattery, Science 191 (1976) 557–559.

[8] R.E. Lacey, Energy by reverse electrodialysis, Ocean Engin. 7 (1980) 1–47.[9] R.K. Nagarale, G.S. Gohil, V.K. Shahi, Adv. Colloid Chem. Interface Sci. 119 (2006)

97–130.[10] Y. Tsunoda, M. Kato, Compact apparatus for sea water desalination by electrodial-

ysis using ion exchange membranes, Desalination 3 (1967) 66–81.[11] J.W. Post, C.H. Goeting, J. Valk, S. Goinga, J. Veerman, H.V.M. Hamelers, P.J.F.M.

Hack, Towards implementation of reverse electrodialysis for power generationfrom salinity gradients, Desalination Water Treat. 16 (2010) 192–193.

[12] P. Długołe cki, K. Nijmeijer, M. Wessling, Current status of ion exchange mem-branes for power generation from salinity gradients, J. Membrane Sci. 319(2008) 214–222.

[13] P. Długołe cki, A. Benoit, S.J. Metz, K. Nijmeijer, M. Wessling, Practical potential ofreverse electrodialysis as process for sustainable energy generation, J. MembraneSci. 346 (2010) 163–171.

[14] P. Długołecki, P. Ogonowski, S.J. Metz, M. Saakes, K. Nijmeijer, M. Wessling, On theresistances of membrane, diffusion boundary layer and double layer in ion ex-change membrane transport, J. Membrane Sci. 349 (2010) 369–379.

[15] P. Długołecki, A. Gambier, K. Nijmeijer, M. Wessling, Practical potential of reverseelectrodialysis as process for sustainable energy generation, Environ. Sci. Tech. 43(2009) 6888–6894.

[16] P. Długołecki, J. Dabrowska, K. Nijmeijer, M. Wessling, Ion conductive spacers forincreased power generation in reverse electrodialysis, J. Membrane Sci. 347(2010) 101–107.

[17] J. Veerman, M. Saakes, G.J. Metz, G.J. Harmsen, Reverse electrodialysis:perfor-mance of a stack with 50 cells on the mixing of sea and river water, J. Membr.Sci. 327 (2009) 136–144.

[18] J.W. Post, J. Veerman, H.V.M. Hamelers, G.J.W. Euverink, S.J. Metz, K. Nymeijer, C.J.N. Buisman, Salinity gradient power: evaluation of pressure-retarded osmosisand reverse electrodialysis, J. Mebrane Sci. 288 (2007) 218–230.

[19] J. Veerman, M. Saakes, S.J. Metz, G.J. Harmsen, Reverse electrodialysis: evaluationof suitable electrode systems, J. Appl. Electrochem. 327 (2009) 136–144.

[20] Y. Tanaka, Mass transport and energy consumption in ion-exchange membraneelectrodialysis of seawater, J. Membr. Sci. Energy 215 (2003) 265–279.

[21] W.P. Harkare, S.K. Adhiry, P.K. Narayanan, V.B. Bhayani, Desalination of brackishwater by electrodialysis, Desalination 42 (1982) 97–105.

[22] S. Shi, P.-Q. Chen, Design and field trials of a 200 m3/day sea water desalination byelectrodialysis, Desalination 46 (1983) 191–196.

[23] M.R. Adiga, S.K. Adhikary, P.K. Narayanan,W.P. Harkare, S.D. Gomkale, K.P. Govindan,Performance analysis of photovoltaic electrodialysis desalination plant at Tanote inThar desert, Desalination 67 (1987) 59–66.

[24] M. Demircioglu, N. Kabay, I. Kurucaovali, E. Ersoz, Demineralization by electrodi-alysis (ed) – separation performance and cost comparison for monovalent salts,Desalination 153 (2002) 329–333.

[25] H.-J. Lee, F. Sarfert, H. Strathmann, S.-H. Moon, Designing of an electrodialysis de-salination plant, Desalination 142 (2002) 267–286.

[26] S. Trasatti, Electrodes of Conductive Metallic Oxides, Elsevier Sci. PublishingComp, 1980.

[27] S. Trasatti, Electrodes of Conductive Metallic Oxides, Elsevier Sci. PublishingComp, 1981.

[28] J.W. Post, H.V.M. Hamelers, C.J.N. Buisman, Influence of multivalent ions on powerproduction from mixing salt and fresh water with a reverse electrodialysis sys-tem, J. Membrane Sci. 330 (2009) 65–72.

[29] J. Newman, K.E. Thomas-Alyea, Electrochemical Systems, 3 rd edition, JohnWiley,2004.

[30] J.J. Goodling, Nanostructuring electrodes with carbon nanotubes: a review onelectrochemistry and applications for sensing, Electrochim. Acta 50 (2005)3049–3060.

[31] C. Liu, H. ans Song, L. Zanh, H. Wang, D.P. Wilkinson, A review of anode catalysisin the direct methanol fuel cell, J. Power. Sources 155 (2006) 95–110.

[32] T.J. Schmidt, H.A. Gasteiger, G.D. Stäb, P.M. Urban, D.M. Kolb, R.J. Behm, Character-ization of high-surface-area electrocatalysts using a rotating disk electrode con-figuration, J. Electrochem. Soc. 145 (1998) 2354–2358.

[33] R.C. Weast, CRC handbook of chemistry and physics, 58th edition, CRC PRESS, Inc,1977.