Device for producing electricity

Abstract

The invention relates to a device (1) for producing electricity, the device (1) comprising a cell (2), the cell having two compartments (31, 32), wherein each compartment has a surface (41, 42) for adsorbing a predetermined ion, and the two compartments are separated by a membrane (5) that is porous to at least the predetermined ion. The two compartments are each intended to receive a liquid (L1, L2) having different concentrations of the predetermined ion. The cell comprises two terminals (61, 62) respectively connected to the adsorption surfaces of the two compartments, which cell is capable of creating a difference in potential Eocv across its two terminals in the presence of the respective liquids in the two compartments. The device (1) further comprises a voltage generator (7), the generator (7) comprising two terminals (71, 72), one (71) of which is connected to a terminal (62) of the cell, the generator being arranged to produce a difference in potential E0 across its two terminals; the other terminal (72) of the generator constitutes one terminal (82) of the device, and the other terminal (81) of the device consists of the other terminal (61) of the cell.

Description

[0001] DESCRIPTION

[0002] Electricity production device

[0003] Technical field

[0004] The present invention relates to the field of renewable energies and, in particular, the production of electricity.

[0005] The present invention relates in particular to blue energy, i.e. the recovery of energy from the change in free enthalpy of a system by combining two solutions having a different concentration of an ionic species.

[0006] A popular application in this field is to exploit the difference in salinity of a mixture of fresh water and sea water.

[0007] State of the prior art

[0008] The method known in the state of the art is called "pressure-delayed osmosis". This technique is based on the phenomenon of osmosis. In practice, this technique is based on the diffusion of water molecules from a compartment containing fresh water to another compartment containing salt water, through a semi-permeable membrane separating the two compartments. This mass transfer increases the quantity of liquid present in the salt water compartment, which generates a difference in hydrostatic pressure between the two compartments, constituting exploitable hydraulic energy.

[0009] Also known in the state of the art are "reverse electrodialysis" and the technique known as "capacitive mixing". These techniques aim to exploit the energy generated by the diffusion of ions induced by the difference in salinity of solutions separated by a selective membrane. Faradic electrodes, in the case of reverse electrodialysis, and capacitive electrodes, in the case of capacitive mixing, are immersed in the solutions and convert the ionic flow into electric current.

[0010] In the case of electrodialysis, the cell comprises a series of compartments separated from each other by a membrane porous to anions or cations. It is the successive and selective diffusions of ions and anions through the compartments that generates the recovered current. In the case of capacitive mixing, it is the successive and alternating filling of the two compartments of the cell with a solution concentrated in a given ion and then with a solution with a low concentration of this given ion that generates the recovered current.

[0011] One of the major challenges for all of these techniques lies in improving the efficiency of the energy produced and, in the case of electricity production, the power density.

[0012] An aim of the invention is, in addition, to propose a device for producing electricity:

[0013] - allowing more energy to be recovered from systems consisting of the combination of two solutions with a different concentration of an ionic species,

[0014] - whose power density produced is greater than that produced by state-of-the-art devices.

[0015] Presentation of the invention

[0016] For this purpose, an electricity production device, called a device, is proposed, comprising a cell. The cell comprises two compartments. Each compartment comprises an adsorption surface for one or more predetermined ions and said two compartments are separated by a membrane porous to at least the predetermined ion. The two compartments are intended to each receive a liquid whose concentration of the predetermined ion is different. The cell comprises two terminals respectively connected to the adsorption surfaces of the two compartments. The cell is capable of generating a potential difference E 0C v between its two terminals in the presence of the respective liquids in the two compartments.

[0017] The device further comprises a voltage generator, called a generator. The device further comprises two terminals. The generator comprises two terminals. One of the two terminals of the generator is connected to one of the two terminals of the cell, the other of the two terminals of the generator constitutes a terminal of the device and the other of the two terminals of the device is constituted by the other terminal of the cell. The generator is arranged to deliver a potential difference Eo between its two terminals. The device may comprise a control unit arranged and / or programmed and / or configured to command and / or control the generator and / or means for supplying the device and / or the cell.

[0018] Preferably, the liquids intended to fill the compartments comprise several ions, for example at least one anion and at least one cation. Preferably, the liquids comprise several ions including the predetermined ion.

[0019] Preferably, the membrane is porous to ensure or allow the exchange of ions between the compartments and / or to ensure or allow the circulation or conduction of electric current in, and / or through, the cell and / or the compartments.

[0020] Preferably:

[0021] - the terminal of the cell to which the terminal of the generator is connected constitutes the negative polarity terminal of the cell and the generator is arranged so that, or the control unit is arranged and / or programmed and / or configured so that, said terminal of the generator connected to the terminal of the cell constitutes the positive polarity terminal of the generator, and / or

[0022] - the terminal of the cell to which the terminal of the generator is connected constitutes the positive polarity terminal of the cell and the generator is arranged so that, or the control unit is arranged and / or programmed and / or configured so that, said terminal of the generator connected to the terminal of the cell constitutes the negative polarity terminal of the generator.

[0023] Preferably, a sign of the potential difference Eo applied to the terminals of the generator, in other words a sign of the voltage Eo = V71-V72, is identical to the sign of the potential difference E 0C v generated at the terminals of the cell, in other words at the sign of the voltage E 0C v = 61- 62.

[0024] Preferably, the potential difference Edis across the terminals of the device, in other words the voltage Edis = si- 82 = 61- 72, is equal to the sum of the potential difference E 0Cv at the terminals of the cell, in the presence of the respective liquids in the two compartments, and the potential difference Eo at the terminals of the generator, in other words E is — Eocv + Eo.

[0025] Preferably, the generator is arranged to, or the control unit is arranged and / or programmed and / or configured to, switch and / or adapt and / or select the polarity of its terminals so that the terminal of the generator connected to the cell terminal is of reverse polarity to the terminal of the cell to which it is connected. Preferably, the adsorption surfaces of the predetermined ion are liquid-porous layers which are intended to receive the two compartments.

[0026] Preferably, each compartment comprises an electrode, an external surface of which constitutes the adsorption surface of the at least one predetermined ion.

[0027] The external surface of the electrode can be defined as the surface of the electrode which is intended to come into contact with the liquid(s).

[0028] The electrode of one of the two compartments may be different from, or made of the same material, as, the electrode of the other of the two compartments. Preferably, the electrodes of each compartment are identical or made of the same material.

[0029] Preferably, the electrode of a compartment, or each electrode of each compartment, is a capacitive electrode.

[0030] Preferably, the membrane is porous only to the predetermined ion.

[0031] Preferably, the adsorption surfaces are specific to the predetermined ion. Preferably, the adsorption surfaces are specific to the predetermined ion such that only the predetermined ion adsorbs on the adsorption surfaces or the predetermined ion is the ion primarily adsorbed on the adsorption surfaces.

[0032] The adsorption surfaces may be non-specific to the predetermined ion. The adsorption surfaces may be non-specific such that one or more ions, other than the predetermined ion, contained in the liquids intended to be received in the compartments adsorb(s) on the adsorption surfaces.

[0033] The porous membrane can be a selective membrane or a non-selective membrane.

[0034] Preferably, the porous membrane is a selective membrane. Preferably, the porous membrane is arranged so that only the predetermined ion diffuses or passes through the selective membrane. Preferably, the porous membrane is an ion selective membrane. Preferably, the selective membrane is porous to one type of ion, preferably to only one type of ion, for example to anions or cations or, more preferably, to one type of cation or one type of anion. Preferably, the selective membrane is porous to a predetermined type of ion. Preferably, the selective membrane is impermeable to ions other than the predetermined type of ion and to molecules (ionic or not), in particular to molecules constituting the liquid(s). Preferably, the at least one predetermined ion belongs to the predetermined type of ion.

[0035] Preferably, the selective membrane is porous to cations or anions. Preferably, the selective membrane is porous to a single type of cations, for example to sodium ions (Na + ), potassium (K + ) or to protons (or hydronium ions), or to a single type of anion, for example to chloride ions (Cl'), hydroxide ions (OH'), bromide ions (Br), sulfate ions (SO4 2 ') or nitrate ions (NO3'). In this application, protons or hydronium ions are considered as cations.

[0036] Preferably, the generator is arranged to deliver a non-zero potential difference Eo. Preferably, the generator is arranged to deliver a potential difference Eo lower than the absolute value of an oxidation-reduction potential, denoted redox, s, of the liquids, preferably than an oxidation-reduction potential Vredox, s of the solvent molecule constituting the liquids, and / or than the absolute value of an oxidation-reduction potential, denoted Vredox, of the at least one predetermined ion and / or than the absolute value of an oxidation-reduction potential of each of the ions contained in the liquids (LI, L2).

[0037] The absolute value of the redox potential V re dox,s can be defined as the potential beyond which electrolysis of the solvent constituting the liquid is initiated. The absolute value of an oxidation-reduction potential of a considered ion can be defined as the potential beyond which oxidation or reduction.

[0038] Preferably, the generator is arranged to deliver a potential difference Eo of less than 5 Volts, preferably 4 Volts, preferably 3 Volts and even more preferably 2 Volts.

[0039] Preferably, the generator is arranged to apply an alternating potential difference Eo.

[0040] Preferably, the alternating potential difference Eo is periodic. Preferably, a period of the periodic alternating potential difference Eo is greater than or equal to 10 seconds.

[0041] Preferably, the period of the alternating potential difference Eo is adapted and / or synchronized and / or equal to a saturation or charging duration of the generator, in particular of the adsorption surfaces. The term saturation or charging duration of the generator or of the adsorption surfaces may be understood to mean the time between the liquids being brought into contact with their respective compartment and the saturation with ions, in particular with the predetermined ion, of the ion adsorption surfaces.

[0042] Preferably, the polarity of the terminals of the cell is reversed after each discharge of the cell. Discharge of the cell may be understood to mean the flow of a current, for example in an electrical resistor connected to the terminals of the electricity production device, generated by the closing of an electrical circuit comprising the electricity production device.

[0043] The voltage may vary, for example linearly, over one or more periods. Preferably, the voltage Eo is constant during each period, i.e. the applied periodic alternating voltage Eo corresponds to or is a rectangular signal.

[0044] Preferably, the device comprises supply means arranged to supply the compartments with liquids). Preferably, the supply means are arranged to supply one of the two compartments with the liquid having a concentration Cl in the predetermined ion and the other of the two compartments with the liquid having a concentration C2, lower than Cl, in the predetermined ion, and vice versa.

[0045] Preferably, the supply means are arranged to successively supply each of the compartments with solutions L1 and L2.

[0046] Preferably, the feeding means are arranged to:

[0047] - inject the solution L1, or respectively L2, into one of the compartments and inject the solution L2, or respectively L1, into the other of the compartments, then

[0048] - after a given time interval, inject the solution L2, or respectively Ll, into said compartment and inject the solution Ll, or respectively L2, into the other of the compartments.

[0049] Preferably, a period between two successive supplies of liquids to the compartments is equal to the period of the alternating potential difference Eo applied by the generator.

[0050] Preferably, the device, or the generator and / or the control means and / or the cell and / or the processing unit, is arranged to introduce a phase shift between the successive supplies of liquids to the compartments, in other words between the successive injections of liquids L1 and L2 into the compartments, and the alternating periodic signal of the voltage Eo applied by the generator.

[0051] Preferably, the device comprises at least two cells connected in series.

[0052] Two or more cells connected in series can be defined as a series cell assembly.

[0053] Preferably, when the device comprises at least two cells in series, the generator is arranged to deliver a potential difference Eo greater than or equal to the sum of the voltages E 0C v generated at the terminals of the cells in the presence of the respective liquids in the cell compartments.

[0054] Preferably, when the device comprises at least two cells in series, the generator is arranged to deliver a potential difference Eo less than:

[0055] - a potential, noted V app ,s, equal to the product of the oxidation-reduction potential of the redox liquids, s by the number of cells in series, noted n, forming the device, in other words to V app s = nx V redox s , and / or

[0056] - a potential, noted V app ,i, equal to the product of the oxidation-reduction potential of the at least one predetermined Vredox ion by the number of cells in series, noted n, forming the device, in other words to V app i = nx V red0X i .

[0057] Preferably, when the device comprises at least two cells in series, the device comprises individual power supply means for each cell.

[0058] Preferably, when the device comprises at least two cells in series, one of the two terminals of the generator is connected to one of the two terminals of the assembly of cells in series, the other of the two terminals of the generator constitutes the second terminal of the device and the other of the two terminals of the assembly of cells in series constitutes the second terminal of the device.

[0059] Preferably, there is also provided a method of producing electricity comprising the steps of:

[0060] - generating a potential difference between two terminals of a cell comprising two compartments from a difference in predetermined ion concentration between two liquids contained or intended to be contained, each, in one of the two respective compartments; each compartment comprises an adsorption surface for the predetermined ion, the two terminals of the cell are respectively connected to the adsorption surfaces of the two compartments and said two compartments are separated by a membrane porous to at least the predetermined ion,

[0061] - applying, by means of a voltage generator, called a generator, a potential difference Eo between the two terminals of the voltage generator; one terminal of the generator is connected to one of the two terminals of the cell, the other terminal of the generator constitutes one of the two terminals of the electricity production device, comprising the cell and the generator, and the other terminal of the device is constituted by the other terminal of the cell.

[0062] Preferably, the electricity production device according to the invention is suitable, more preferably is particularly suitable, more preferably is designed and particularly advantageously is specially designed, for implementing the electricity production method according to the invention. Also, any characteristic of the electricity production device according to the invention is directly transposable and integrable to the electricity production method according to the invention and vice versa.

[0063] Description of figures

[0064] Other advantages and particularities of the invention will appear on reading the detailed description of implementations and embodiments which are in no way limiting, and the following appended drawings:

[0065] [Fig. 1] FIGURE 1 is a schematic representation in side view of an embodiment of an electricity production device according to the invention at the end of the injection of the liquids LI, L2 into their respective compartment during a given period,

[0066] [Fig. 2] FIGURE 2 is a schematic representation in side view of an embodiment of an electricity production device according to the invention at the end of the injection of the liquids LI, L2 into their respective compartment during a period following a period as illustrated in FIGURE 1,

[0067] [Fig. 3] FIGURE 3 is a graph illustrating the curves, obtained by chronovoltammetry, of the voltage Eioad at the terminals of the external resistance Rioad, in solid lines, for several potential differences Eo, in dotted lines, delivered by the generator during several successive periods,

[0068] [Fig. 4] FIGURE 4 is a graph illustrating the net power density curves as a function of Rioad obtained by the cell, denoted Pnb, and the net power density curves as a function of Rioad obtained by the electricity production device, denoted Pb-net, for a potential difference Eo delivered by the generator of 550 mV,

[0069] [Fig. 5] FIGURE 5 is a histogram illustrating the net power densities Pnb supplied by the cell and the net power densities Pb-net supplied by the device for several potential differences Eo delivered by the generator,

[0070] [Fig. 6] FIGURE 6 is a graph illustrating the net power density curves as a function of Rioad obtained by cell 2, denoted Pnb, and the net power density curves as a function of Rioad obtained by the electricity production device, denoted Pb-net, for several potential differences Eo delivered by the generator,

[0071] [Fig. 7] FIGURE 7 is a graph illustrating the net power density curves as a function of Rioad obtained by cell 2, denoted Pnb, and the net power density curves as a function of Rioad obtained by the electricity production device, denoted Pb-net, for several potential differences Eo delivered by the generator, [Fig. 8] FIGURE 8 is a schematic representation in side view of an improvement of the embodiment of the electricity production device according to the invention at the end of the injection of the liquids LI, L2 into their respective compartments 31, 32 during a given period,

[0072] [Fig. 9] FIGURE 9 is a graph illustrating the net power density curve, denoted Pb-net, as a function of Rioad obtained by the electricity production device according to the improvement illustrated in FIGURE 8 for a potential difference Eo delivered by the generator of 0 mV.

[0073] Description of the embodiments

[0074] The embodiments described below being in no way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of the described characteristics, isolated from the other described characteristics (even if this selection is isolated within a sentence comprising these other characteristics), if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one characteristic, preferably functional without structural details, or with only a part of the structural details if this part only is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0075] With reference to FIGURES 1 and 2, an embodiment of the electricity production device 1 according to the invention is presented. The device 1 comprises a cell 2. The cell 2 comprises two compartments 31, 32. Each compartment 31, 32 comprises an adsorption surface 41, 42 for a predetermined ion. The two compartments 31, 32 are separated by a porous membrane 5 containing at least the predetermined ion. The two compartments 31, 32 are each intended to receive a liquid LI, L2 having a different concentration of the predetermined ion. The cell 2 comprises two terminals 61, 62 respectively connected to the adsorption surfaces 41, 42 of the two compartments 31, 32. The cell 2 is capable of generating a potential difference E 0Cv between its two terminals 61, 62 in the presence of the respective liquids LI, L2 in the two compartments 31, 32. The device 1 comprises a voltage generator 7. The generator 7 comprises two terminals 71, 72. One terminal 71 of the generator 7 is connected to the terminal 62 of the cell 2 and the other terminal 72 of the generator 7 constitutes a terminal 82 of the device 1. The other terminal 81 of the device 1 is constituted by the other terminal 61 of the cell 2. The generator 7 is arranged to deliver a non-zero potential difference Eo between its two terminals 71, 72.

[0076] The cell 2 is of the salinity gradient capacitive type. Also, when the cell 2 is in open circuit, the contacting of two liquids LI, L2, of which a predetermined ion is in different concentration, with the two respective adsorption surfaces 41, 42, for example the liquid L1 in contact with the adsorption surface 41 and the liquid L2 in contact with the adsorption surface 42, will cause the appearance of a potential difference at the terminals 61, 62 of the cell 2. This is due to the selective diffusion of the at least one ion through the membrane 2, which generates a difference in salinity between the two compartments 31, 32, and to a different variation in the potential of one electrode 41, 42 relative to the other 42, 41 due to the variation in the concentration of the at least one ion in the compartments 31, 32.Closing the circuit, i.e. connecting terminals 61, 62 of cell 2 to the terminals of a resistor, will cause a current to flow in the resistor and a drop in the capacitive potential difference between the two adsorption surfaces 41, 42 and therefore at the terminals of cell 2. The current generated will therefore decrease with the decrease in the potential difference at the terminals of cell 2. At that moment, when cell 2 is "discharged", liquids LI, L2 are removed from their respective compartments 31, 32. Then, liquid L1 will be placed in compartment 32 and liquid L2 will be placed in compartment 31 to initiate a new cycle (or new period). In this way, a current can be recovered periodically from cell 2 by successive injections and withdrawals of liquids LI, L2 in compartments 31, 32.In the present application, the term period T of the cell 2 or the device 1 is understood to mean the time separating two successive injections of the liquids LI, L2 into the compartments 31, 32; that is to say the injection of the liquid L1 into the compartment 31 and the injection of the liquid L2 into the compartment 32, during a period T considered, followed by the injection of the liquid L1 into the compartment 32 and the injection of the liquid L2 into the compartment 31, during a period T+1 following the period T considered, and vice versa. FIGURE 1 represents the state of the device 1 at the end of the injection of the liquids LI, L2 into their respective compartments 31, 32 during a period T considered. FIGURE 2 represents the state of the device 1 at the end of the injection of the liquids LI, L2 into their respective compartments 31, 32 during a period T+1 following the period T considered.The phase, or phase shift, between the period of cell 2 and the period of the voltage delivered by generator 7 is as small as possible, ideally equal to zero.

[0077] According to the embodiment, means 9 for supplying the compartments with liquids LI, L2 are shown. However, these supply means 9 are known and are not part of the device 1. The cell 2 is only capable of cooperating with these supply means 9 which are intended to be mounted on the cell 2. The supply means 9 comprise two circuits 91, 92 respectively connecting the compartments 31, 32 to a permutation means 93, for example a pneumatic valve 93, arranged to control the injection of the liquids LI, L2 into one of the circuits 91, 92. The supply means 9 comprise a pump arranged to regulate and control the injection flow rate of the liquids LI, L2 into the circuits 91, 92.

[0078] According to a first non-limiting embodiment, the solutions used to illustrate the operation and performance of the device 1 according to the invention are aqueous solutions LI, L2 comprising Sodium Chloride NaCl at two different concentrations. The operation of the device 1 is therefore based on a difference in concentration of a predetermined ion, in Sodium Na ions +or Chloride Cl' according to the first embodiment, in the two liquids LI, L2. According to this first embodiment, in practice and the intended applications, the two liquids which are envisaged for use in the salinity gradient capacitive cells are seawater and fresh water in order to exploit their difference in salinity. The membrane 5 is a cationic ion exchange membrane made of sulfonate tetrafluoroethylene or NAFION™, model NAFION™ 117, sold by the company Chemours®, having a thickness of 183 μm in its dry form. The adsorption surfaces 41, 42 are made of carbon felt, have a geometric surface area of ​​approximately 2.2 cm 2and are separated by 1.5 mm from each other. Two graphite current collectors are respectively connected to the adsorption surfaces 41, 42. Each compartment 31, 32 has a volume of approximately 0.34 cm3. The carbon felt adsorption surfaces 41, 42 act as capacitive electrodes. A ratio of fifty between the NaCl concentrations in liquids L1 and L2 was used, liquid L1 has a NaCl concentration of 5.13 mol / L and liquid L2 has a concentration of 0.17 mol / L. The filling rate of compartments 31, 32 is 10 mL / min according to the first embodiment. FIGURE 1 illustrates the beginning of a period T when liquid L1 with the highest concentration is injected into compartment 31, the Na cations +have not diffused through the membrane 5 at this stage. FIGURE 2 illustrates the beginning of a period T when the liquid L1 with the highest concentration is injected into compartment 32, the Na cations +have not at this stage diffused through the membrane 5. In the dotted inserts of FIGURES 1 and 2 is shown the equivalent circuit of cell 2 during its discharge in the external resistance, denoted Rioad. The equivalent circuit of cell 2 includes an internal resistance Rceii and a capacitance Cceii. The potential difference Eceii at the terminals 61, 62 of cell 2 is equal to the sum of the Donnan potential, generated by the membrane 5, and the potential between the adsorption surfaces 41, 42 reduced by the potential drop induced by the capacitance Cceii of cell 2. When cell 2 is in open circuit, the dropout potential, noted Eocv, of cell 2 is approximately equal to 144 millivolts (mV), the resistance Rœii of cell 2 is approximately equal to 5.39 ohms (Q) and the capacitance Cceii of cell 2 is approximately 1.27 Farads (F).

[0079] The graph in FIGURE 3 shows the curves from the chronovoltammetry measurements of the voltage Eioad across the external resistor Rioad, in solid lines, for several potential differences Eo, in dotted lines, delivered by the generator 7, for a load resistor Rioad set at 75 Q and for several successive periods T of 45 seconds each.

[0080] The graph in FIGURE 4 illustrates the net power density curves as a function of Rioad obtained by cell 2, denoted Pnb, used alone (without generator 7) and the net power density curves as a function of Rioad obtained by device 1, denoted Pb-net, for a potential difference Eo delivered by generator 7 of 550 mV. In the present description, the net power density Pnb supplied by cell 2 corresponds to the power produced by cell 2 used alone (without generator 7) and the net power density Pb-net supplied by device 1 according to the invention as illustrated in FIGURES 1, 2 and 8. In the case of cell 2, the net power density Pnb is the power density dissipated in the external resistance Rioad.In the case of device 1, the net power density Pb-net is calculated as the difference between the power density dissipated by device 1 in the external resistor Rioad over the discharge duration and the power density supplied by generator 7 over the discharge duration. It is surprising to observe that for external resistor values ​​Rioad greater than 30 Ohms, the net power density Pb-net of device 1 is greater than the net power density Pnb of cell 2. In other words, the net power density Pb-net supplied by device 1 is greater than the sum of the net power density Pb-net supplied by cell 2 during the discharge and the power density supplied by generator 7 during the discharge. Device 1 achieves a maximum net power density of 3.35 Wm -2, which corresponds to an increase of 45.4% compared to the maximum net power density achieved by cell 2. With reference to Tables 1, 2 and 3, the comparative results, in terms of gain, between device 1 and cell 2 are illustrated. The gain is expressed in percent and corresponds to the ratio between (i) the difference between the net power density Pb-net provided by device 1 and the net power density Pnb provided by cell 2 and (ii) the net power density Pnb provided by cell 2, i.e. Gain = (Pb-net - Pnb) / Pnb . The net power densities provided by device 1 and cell 2 were measured for several differences in NaCI concentration in the liquids LI, L2 and for several periods T.Regarding the net power density Pb-net provided by device 1, it was also measured for several potential differences Eo delivered by generator 7 and for each potential difference Eo considered the external resistance Rioad giving the optimal results, noted Rmax, was used. The results presented in table 1 were obtained with a device 1 comprising a membrane 5 in NAFION™ 117, those in table 2 with a device 1 comprising a membrane 5 Fumasep FKS-30 sold by the company Fumatech® whose thickness is between 26 and 30 pm and those in table 3 with a device 1 comprising a membrane 5 NAFION HP sold by the company Chemours® whose thickness is 22 pm. It is observed that whatever the membrane 5 used, the performances of device 1 increase then decrease when the period T is greater than a value between 40 and 60 seconds.It should be noted that this period T depends on the cell 2 used (type of adsorption surface 41, 42, volume of compartments 31, 32, volume of solutions L1, L2, type of solution, nature of ions in solution and of the at least one ion, thickness of membrane 5, type of connectors, etc.). It should also be noted that the performances increase when the potential difference Eo delivered by generator 7 increases. It can also be noted that increasing the ratio between the NaCl concentrations in liquids L1 and L2 beyond a certain threshold induces a drop in the performances of device 1.

[0081]

[0082] Table 1

[0083] Table 2

[0084] Table 3

[0085] FIGURE 5 shows a histogram illustrating the net power densities Pnb provided by cell 2 alone, i.e. for a zero potential difference Eo, in other words in the absence of generator 7, and the net power densities Pb-net provided by device 1 for potential differences Eo delivered by generator 7 of 200, 550 and 800 mV. The external resistance ioad giving the optimal results, noted Rmax, was used. The measurements were carried out with each of the membranes 5: FKS-30, Nation 117 and Nation HP. For each Eo a resistance range from 0.1 to 300 was tested.

[0086] In the case of device 1 comprising the FKS-30 membrane 5, the abandonment potential E 0C v of cell 2 and cell resistance Rœii are 157 mV and 6.08 Q respectively. A net power density Pb-net provided by device 1 is 4.01 W.nr 2for an optimal resistance Rmax of 75 Q. The net power density Pb-net provided by device 1 corresponds to an increase of 45% compared to the net power density Pnb of 2.75 W.nr 2 provided by cell 2.

[0087] In the case of device 1 comprising the 5 Nafion HP membrane, the abandonment potential E 0C v of cell 2 and cell 2 resistance Rceii are 158 mV and 4.92 Q respectively. These values ​​are slightly better than those displayed by the 5 FKS-30 membrane and are much better than those of Nafion 117 for which the dropout potential E 0C v of cell 2 is 145 mV and the resistance Rceii of cell 2 varies between 5.4 and 6 Q. For the 5 Nafion HP membrane, the best results are obtained for an optimal resistance Rmax of 50 Q. A net power density Pb-net of 5.26 W.nr 2was provided by device 1, which corresponds to an increase of 59.8% compared to the net power density Pnb provided by cell 2.

[0088] The best results obtained for device 1 comprising the 5 Nafion HP membrane are due to the high selectivity and low resistance of this 5 membrane compared to those of the 5 FKS-30 and NAFION 117 membranes. The 5 Nafion 117 membrane has a thickness of 183 pm compared to 22 pm for the Nafion HP and 26-30 pm for the 5 FKS-30 membrane.

[0089] In the context of the first embodiment, it should be noted that the carbon felt adsorption surfaces 41, 42 used are not selective for a predetermined type of ion. Also, the use of adsorption surfaces 41, 42 selective for cations or anions for example, or even more advantageously for a predetermined type of cations or anions, for example for sodium ions Na +, would further increase the performance of device 1.

[0090] In a second non-limiting embodiment, the solutions used to illustrate the operation and performance of the device 1 according to the invention are an aqueous solution, for example L1, of sodium hydrogen carbonate NaHCCh at a concentration of 1 mol / L at a pH of 7.9 and an aqueous solution, for example L2, of sodium carbonate NazCCh at 0.5 mol / L at a pH of 11.64. The solutions L1, L2 therefore have a different concentration of hydronium ions H3O +. The operation of the device 1 is therefore, as for the first embodiment, based on a difference in concentration of a predetermined ion, in hydronium ions in the case of the second embodiment, in the two liquids L1, L2. According to this second embodiment, in practice and the intended applications, it is envisaged to exploit CO2, for example the CO2 emitted by the gases produced during the combustion of fossil fuels or the stale gases loaded with CO2 emitted by industrial, agri-food or agricultural activities. Also, according to the non-limiting embodiment, the difference in pH is obtained by injecting CO2, by bubbling, into one of the compartments 31, 32 containing a solution of Na2CO3 and / or NaHCCh so as to reduce the pH and induce a difference in pH between the two compartments 31, 32.It is also possible to use other ion concentrations in the solutions L1 and L2, other solutions L1 and L2 and / or other pairs of solutions L1 / L2 (inducing different pHs and different pH differences) such as, by way of non-limiting example, the pair K2CO3 / KHCO3 or the pair Na2HPO4 / NaH2PO4. It should be noted that alternatively, the pH difference can be induced by increasing the temperature of the solution L1, L2 contained in one of the compartments 31, 32, for example by injecting into one of the compartments, for example compartment 31, a solution, for example L1, having a temperature higher than the other solution or by heating the compartment, for example 31, to increase the temperature of the solution, for example L1, which it contains.

[0091] According to the second embodiment, the cell 2 and the device 1 are structurally identical to those described for the first embodiment. The operation of the cell 2 is identical and consists of periodically recovering a current by successive and alternating injections and withdrawals of the liquids L1, L2 in the compartments 31, 32. Also, the parameters and operating parameters of the cell 2 and the device 1 not described for the second embodiment are identical to those previously described. The adsorption surfaces 41, 42 have a geometric surface area of ​​approximately 10.1 cm 2 The apparent surface area of ​​membrane 5 is approximately 5.5 cm 2 The thickness of the membrane 5 is approximately 0.3 mm. The injection flow rate of the liquids L1, L2 into the circuits 91, 92 is of the order of 15 mb min. The volume of the compartments 31, 32 is approximately 0.165 cm 3. The porous membrane 5 used is a non-selective membrane 5 of the Celgard 3501 model, sold by the company Celgard®, having a thickness of 25 μm in its dry form and a pore size of 0.064 μm. The injection rate of the liquids LI, L2 in the circuits 91, 92, i.e. the filling rate, is 15 mb / min according to the embodiment. The duration of the period T of such a cell 2 was observed at 60 seconds.

[0092] The adsorption surfaces 41, 42 are made of composite material and have a geometric surface area of ​​approximately 10.15 cm 2. The adsorption surfaces 41, 42 made of composite material act as capacitive electrodes. According to the non-limiting embodiment, the adsorption surfaces 41, 42 made of composite material are made of carbon felt covered with particles having an average size of 200 μm. The particles comprise 70%, by mass, of particles made of manganese (IV) oxide or manganese dioxide MnOz, 20%, by mass, of carbon black and 10%, by mass, of polyvinylidene fluoride. The mass loading of particles is approximately 12.4 mg / cm 2 .

[0093] With reference to FIGURE 6, the net power densities Pnb supplied by cell 2 alone are illustrated, i.e. for a zero potential difference Eo, in other words in the absence of generator 7, and the net power densities Pb-net supplied by device 1 for potential differences Eo delivered by generator 7 of 300, 500 and 700 mV. The ph gradient is 2.4. The net power densities Pnb supplied by cell 2 alone and the net power densities Pb-net supplied by device 1 are presented as a function of the load resistance ioad used. As for the first embodiment, it is observed that the device 1 provides net power densities Pb-net greater than the net power densities Pnb provided by the cell 2 alone, regardless of the load resistance Rioad used and regardless of the potential difference Eo delivered by the generator 7.

[0094] With reference to FIGURE 7, the net power densities Pnb supplied by cell 2 alone are illustrated, i.e. for a zero potential difference Eo, in other words in the absence of generator 7, and the net power densities Pb-net supplied by device 1 for potential differences Eo delivered by generator 7 of 300, 400, 500, 600 and 700 mV. The ph gradient is 3.75. The net power densities Pnb supplied by cell 2 alone and the net power densities Pb-net supplied by device 1 are presented as a function of the load resistance Rioa used. Only the range of optimal resistances Rmax has been reported in FIGURE 7 for each potential difference Eo delivered by generator 7.As for FIGURE 6 and for the first embodiment, it is observed that the device 1 provides net power densities Pb-net greater than the net power densities Pnb provided by the cell 2 alone, regardless of the load resistance Rioad used and regardless of the potential difference Eo delivered by the generator 7.

[0095] It should be noted that the Celgard 3501 membrane 5 used in the second embodiment is a non-selective membrane 5. The use of such a non-selective membrane 5 greatly reduces the performance of the device 1. Also, the use of a selective membrane, for example a membrane selective for cations, even more preferably for hydronium ions, such as a proton exchange membrane, or, for example, a membrane selective for anions, even more preferably for hydroxide ions, would significantly increase the performance of the device 1.

[0096] With reference to FIGURE 8, and in an improvement of the device 1 according to the first embodiment, there is provided a device 1 comprising two cells 2, 21, 22 connected in series and a voltage generator 7. Terminal 61 of cell 2, 21 is connected to terminal 63 of cell 2, 23. Generator 7 comprises two terminals 71, 72, one terminal 71 of which is connected to terminal 62 of cell 2, 21 and the other terminal 82 of which is connected to terminal 64 of cell 2, 22. Generator 7 being arranged to deliver a potential difference Eo between its two terminals 71, 72. Device 1 comprises two terminals 81, 82. Terminal 82 of device 1 is connected to terminal 64 of cell 2, 21 and to terminal 72 of generator 7. The other terminal 81 of the device 1 is connected to terminal 62 of cell 2, 22 and to terminal 72 of the generator 7. The generator 7 is arranged to deliver a non-zero potential difference Eo between its two terminals 71, 72.It should be noted that this improvement applies to any type of cell 2 and liquids LI, L2 according to the invention. Also, this improvement is also applicable, for example, to the second embodiment.

[0097] With reference to FIGURE 9, and according to the improvement of device 1 as illustrated in FIGURE 8, the net power density Pb-net of device 1 is illustrated as a function of the load resistance Rioad for a voltage Eo delivered by generator 7 of 0 mV. The potential difference E 0C v measured between terminals 81, 82 of device 1, or between terminal 64 of cell 2, 22 and terminal 62 of cell 2, 21, in the presence of the respective liquids LI, L2 in the two compartments 31, 32 is 850 mV, i.e. 70 mV less than the sum of the potential differences E 0Cv measured at terminals 61, 62 and 63, 64 of the two cells 2, 21 and 2, 22 taken individually. In addition, the net power values ​​Pb-net of the device 1 are lower by approximately 10% compared to the sum of the net power values ​​Pb-net of the respective devices 1 each comprising an individual cell 2 among the two cells 2, 21, 22. This difference comes from the fact that the solutions LI, L2 entering their respective compartments 31, 32 of the cell 2, 22 see their concentration slightly modified after their passage into their respective compartments 31, 32 of the cell 2, 21. Also, a simple modification of the supply means 9 so that the liquids LI, L2 are injected in parallel directly into the compartments 31, 32 of the cells 2, 21 and 2, 22 would make it possible to avoid the observed loss.

[0098] For each of the embodiments, it is observed that the increase in the potential difference Eo delivered by the generator 7 makes it possible to significantly increase the performance of the device 1 compared to the performance of the cell 2 alone. In particular, the increase in the potential difference Eo delivered by the generator 7 makes it possible to significantly increase the usable load resistance Rjoad. Also, according to the invention it is advantageous to increase the potential difference Eo delivered by the generator 7 when the load resistance Rioad increases. It is also noted that for a given cell 2 and a type of liquids LI, L2 used, the potential difference Eo delivered by the generator 7 has an optimal range depending on the load resistance Rioad used.

[0099] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

[0100] Thus, it is possible to combine the various variants and improvements of the previously described embodiments. In addition, the various features, forms, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

Claims

CLAIMS 1. Electricity production device (1), called device (1), comprising: - a cell (2), said cell comprises two compartments (31, 32), each compartment comprises an adsorption surface (41, 42) of a predetermined ion and said two compartments are separated by a porous membrane (5) to at least the predetermined ion; said two compartments are intended to receive, each, a liquid (LI, L2) whose concentration in the predetermined ion is different, said cell comprises two terminals (61, 62) respectively connected to the adsorption surfaces of the two compartments and is capable of generating a potential difference E 0C v between its two terminals in the presence of the respective liquids in the two compartments, - a voltage generator (7), called generator (7), comprising two terminals (71, 72) of which one terminal (71) is connected to a terminal (62) of the cell, said generator being arranged to deliver a potential difference Eo between its two terminals; the other terminal (72) of the generator constitutes a terminal (82) of the device and the other terminal (81) of the device is constituted by the other terminal (61) of the cell.

2. Device (1) according to claim 1, wherein the terminal (62) of the cell (2) to which the terminal (71) of the generator (7) is connected constitutes the negative polarity terminal of the cell and wherein the generator is arranged so that said terminal (71) of the generator connected to the terminal (62) of the cell (2) constitutes the positive polarity terminal of the generator, or vice versa.

3. Device (1) according to claim 1 or 2, in which the adsorption surfaces (41, 42) of the predetermined ion are liquid-porous layers (LI, L2) which are intended to receive the two compartments (31, 32).

4. Device (1) according to any one of the preceding claims, in which each compartment (31, 32) comprises an electrode (41, 42) of which an external surface constitutes the adsorption surface of the at least one predetermined ion.

5. Device (1) according to the preceding claim, in which the electrode (41, 42) of a compartment (31, 32), or each electrode of each compartment, is a capacitive electrode.

6. Device (1) according to any one of the preceding claims, wherein the porous membrane (5) is porous only to the predetermined ion and / or the adsorption surfaces (41, 42) are specific to the predetermined ion.

7. Device (1) according to any one of the preceding claims, in which the generator (7) is arranged to deliver a potential difference Eo which is not zero and less than the absolute value of an oxidation-reduction potential of the liquids (L1, L2) and / or the absolute value of an oxidation-reduction potential of the at least one predetermined ion.

8. Device (1) according to any one of the preceding claims, in which the generator (7) is arranged to apply an alternating potential difference Eo.

9. Device (1) according to any one of the preceding claims, comprising supply means (9) arranged to supply one (32) of the two compartments (31, 32) with the liquid (L1) having a concentration Cl in the predetermined ion and the other (31) of the two compartments with the liquid (L2) having a concentration C2, lower than Cl, in the predetermined ion, and vice versa.

10. Device (1) according to the preceding claim, in which the supply means (9) are arranged to successively supply each of the compartments (31, 32) with solutions L1 and L2.

11. Device (1) according to the preceding claim taken in combination with claim 8, in which a period between two successive supplies of the compartments (31, 32) with liquids (L1, L2) is equal to the period of the alternating potential difference Eo applied by the generator (7).

12. Device according to any one of the claims, comprising at least two cells (2) connected in series.

13. Method for producing electricity comprising the steps of: - generating a potential difference between two terminals (61, 62) of a cell (2) comprising two compartments (31, 32) from a difference in concentration of predetermined ion between two liquids (L1, L2) each contained in one of the two respective compartments; each compartment comprises an adsorption surface (41, 42) of the predetermined ion, the two terminals of the cell are respectively connected to the adsorption surfaces of the two compartments and said two compartments are separated by a porous membrane (5) to at least the predetermined ion, - applying, by means of a voltage generator (7), called generator, a potential difference Eo between two terminals (71, 72) of the generator; one terminal (71) of the generator is connected to one (62) of the two terminals of the cell, the other terminal (72) of the generator constitutes one (82) of the two terminals (81, 82) of an electricity production device (1), comprising the cell and the generator, and the other terminal (81) of the device is constituted by the other terminal (61) of the cell.

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