Electricity production device

Abstract

"Electricity Generation Device" Electricity generation device (1), referred to as device (1), comprising a cell (2), said cell comprising two compartments (31, 32), each compartment comprising an adsorption surface (41, 42) for a predetermined ion, and said two compartments are separated by a porous membrane (5) permeable to at least the predetermined ion. Each of the two compartments is intended to receive a liquid (L1, L2) having a different concentration of the predetermined ion. The cell comprises two terminals (61, 62) respectively connected to the adsorption surfaces of the two compartments and is capable of generating a potential difference Eocv between its two terminals in the presence of the respective liquids in the two compartments.The device (1) further includes a voltage generator (7), referred to as 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 E0 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. Figure for the abbreviation: Figure 1.

Description

Title of the invention: Electricity production device technical field

[0001] The present invention relates to the field of renewable energies and, in particular, the production of electricity.

[0002] The present invention relates in particular to blue energy, that is to say the recovery of energy from the change in free enthalpy of a system by combining two solutions having a different concentration in an ionic species.

[0003] A widespread application in this field is that of exploiting the difference in salinity of a mixture of fresh water and sea water. Prior art

[0004] The prior art method known as "pressure-retarded osmosis" is based on the phenomenon of osmosis. In practice, this technique relies 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 amount of liquid present in the salt water compartment, which generates a hydrostatic pressure difference between the two compartments, thus providing usable hydraulic energy.

[0005] In the prior art, "reverse electrodialysis" and "capacitive mixing" are also known. These techniques aim to harness the energy generated by ion diffusion induced by the salinity difference 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 flux into an electrical current.

[0006] 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 diffusion of ions and anions through the compartments that generates the recovered current.

[0007] 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 in that given ion that generates the recovered current.

[0008] One of the major challenges for all these techniques lies in improving the efficiency of the energy produced and, in the case of electricity production, the power density.

[0009] One object of the invention is, moreover, to provide a device for producing electricity: - allowing for the recovery of more energy from systems consisting of the combination of two solutions with different concentrations of an ionic species, - whose power density produced is greater than that produced by state-of-the-art devices. Presentation of the invention

[0010] To this end, an electricity generation device, referred to as the device, is proposed, comprising a cell. The cell comprises two compartments. Each compartment includes an adsorption surface for one or more predetermined ion(s), and the two compartments are separated by a membrane porous to at least the predetermined ion. The two compartments are intended to each receive a liquid having a different concentration of the predetermined ion. The cell comprises two terminals respectively connected to the adsorption surfaces of the two compartments. The cell is capable of generating a potential difference Eocv between its two terminals in the presence of the respective liquids in the two compartments.

[0011] The device further comprises a voltage generator, referred to as the 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.

[0012] The device may include a control unit arranged and / or programmed and / or configured to command and / or control the generator and / or means of supplying the device and / or the cell.

[0013] 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.

[0014] 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.

[0015] Preferably: - the cell terminal to which the generator terminal is connected constitutes the negative polarity terminal of the cell, and the generator is arranged, or the control unit is arranged and / or programmed and / or configured, so that said generator terminal connected to the cell terminal constitutes the positive polarity terminal of the generator, and / or - the cell terminal to which the generator terminal is connected constitutes the positive polarity terminal of the cell and the generator is arranged so, or the control unit is arranged and / or programmed and / or configured so, that said generator terminal connected to the cell terminal constitutes the negative polarity terminal of the generator.

[0016] Preferably, a sign of the potential difference Eo applied across the terminals of the generator, in other words a sign of the voltage Eo = V7i-V72, is identical to the sign of the potential difference Eocv generated across the terminals of the cell, in other words the sign of the voltage Eocv = V6j-V62.

[0017] Preferably, the potential difference Edis across the terminals of the device, in other words the voltage Edis = V8i-V82 = V6rV72, is equal to the sum of the potential difference Eocv across the terminals of the cell, in the presence of the respective liquids in the two compartments, and the potential difference Eo across the terminals of the generator, in other words E dis — Eocv + Eo.

[0018] 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 the opposite polarity to the cell terminal to which it is connected.

[0019] Preferably, the adsorption surfaces of the predetermined ion are liquid-porous layers intended to receive the two compartments.

[0020] Preferably, each compartment includes an electrode whose external surface constitutes the adsorption surface of at least one predetermined ion.

[0021] 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).

[0022] 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.

[0023] Preferably, the electrode of a compartment, or each electrode of each compartment, is a capacitive electrode.

[0024] Preferably, the membrane is porous only to the predetermined ion.

[0025] 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 onto the adsorption surfaces, or that the predetermined ion is the ion primarily adsorbed onto the adsorption surfaces.

[0026] 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) onto the adsorption surfaces.

[0027] The porous membrane can be a selective membrane or a non-selective membrane.

[0028] Preferably, the porous membrane is a selective membrane. Preferably, the porous membrane is arranged so that only the predetermined ion diffuses through 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 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 non-ionic), in particular to molecules constituting the liquid(s). Preferably, at least one predetermined ion belongs to the predetermined type of ion.

[0029] Preferably, the selective membrane is porous to cations or anions. Preferably, the selective membrane is porous to only one type of cation, for example sodium (Na+), potassium (K+) ions or protons (or hydronium ions), or to only one type of anion, for example chloride (Cl-), hydroxide (OH-), bromide (Br-), sulfate (SO42-) ions or nitrate (NO3-) ions. In this application, protons or hydronium ions are considered to be cations.

[0030] Preferably, the generator is arranged to deliver a non-zero potential difference Eo. Preferably, the generator is arranged to deliver a potential difference Eo less than the absolute value of a redox potential, denoted VredOXjS, of the liquids, preferably than a redox potential VredOXjS of the solvent molecule constituting the liquids, and / or than the absolute value of a redox potential, denoted VredOX>i, of at least one predetermined ion and / or than the absolute value of a redox potential of each of the ions contained in the liquids (L1, L2).

[0031] The absolute value of the redox potential VredOXjS can be defined as the potential beyond which electrolysis of the solvent constituting the liquid is initiated. The absolute value of a redox potential of a considered ion can be defined as the potential beyond which oxidation or reduction occurs.

[0032] 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.

[0033] Preferably, the generator is arranged to apply an alternating potential difference Eo.

[0034] Preferably, the alternating potential difference Eo is periodic. Preferably, one period of the periodic alternating potential difference Eo is greater than or equal to 10 seconds.

[0035] Preferably, the period of the alternating potential difference Eo is adapted and / or synchronized and / or equal to a saturation or charging time of the generator, in particular of the adsorption surfaces. The saturation or charging time of the generator or the adsorption surfaces can be understood as the time between the contact of the liquids with their respective compartment and the saturation of the ion adsorption surfaces with ions, in particular with the predetermined ion.

[0036] Preferably, the polarity of the cell terminals is reversed after each cell discharge. A cell discharge can be understood as the flow of current, for example in an electrical resistor connected to the terminals of the power-generating device, generated by the closing of an electrical circuit including the power-generating device.

[0037] The voltage can vary, for example linearly, during one or more periods. Preferably, the voltage Eo is constant during each period; in other words, the applied periodic alternating voltage Eo corresponds to, or is, a rectangular signal.

[0038] Preferably, the device includes feeding means arranged to supply the compartments with liquid(s). Preferably, the feeding means are arranged to supply one of the two compartments with the liquid having a concentration Cl of the predetermined ion and the other of the two compartments with the liquid having a concentration C2, lower than Cl, of the predetermined ion, and vice versa.

[0039] Preferably, the feeding means are arranged to successively supply each of the compartments with solutions L1 and L2.

[0040] Preferably, the feeding means are arranged to: - inject solution L1, or respectively L2, into one of the compartments and inject solution L2, or respectively L1, into the other compartment, then - after a given time interval, inject solution L2, or respectively L1, into said compartment and inject solution L1, or respectively L2, into the other of the compartments.

[0041] Preferably, a period between two successive liquid supplies to the compartments is equal to the period of the alternating potential difference Eo applied by the generator.

[0042] 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 successive liquid supplies to the compartments, in other words between the in successive injections of liquids L1 and L2 into the compartments, and the alternating periodic signal of the voltage Eo applied by the generator.

[0043] Preferably, the device comprises at least two cells mounted in series.

[0044] The at least two cells mounted in series can be defined as an assembly of cells mounted in series.

[0045] 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 Eocv generated across the terminals of the cells in the presence of the respective liquids in the compartments of the cells.

[0046] Preferably, when the device comprises at least two cells in series, the generator is arranged to deliver a potential difference Eo less than: - a potential, denoted Vapp,s, equal to the product of the redox potential of the liquids VredOx,s by the number of cells in series, denoted n, forming the device, in other words Vapp,x = nx V redox^ and / or - a potential, denoted Vapp>i, equal to the product of the redox potential of at least one predetermined ion VredOx,i and the number of cells in series, denoted n, forming the device, in other words, Vappj — HX Vrejax P

[0047] Preferably, when the device includes at least two cells in series, the device includes individual power supply means for each cell.

[0048] 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.

[0049] Preferably, a method for producing electricity is also proposed, comprising the steps of: - to generate a potential difference between two terminals of a cell comprising two compartments from a predetermined ion concentration difference 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, - apply, by means of a voltage 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 production device of electricity, including the cell and the generator, and the other terminal of the device is constituted by the other terminal of the cell.

[0050] Preferably, the electricity generation device according to the invention is suitable, more preferably is particularly adapted, even more preferably is designed, and most advantageously is specially designed, for implementing the electricity generation process according to the invention. Furthermore, any feature of the electricity generation device according to the invention is directly transferable and integrable into the electricity generation process according to the invention, and vice versa. Description of the figures

[0051] Other advantages and features of the invention will become apparent upon reading the detailed description of implementations and embodiments, which are by no means limiting, and the following accompanying drawings:

[0052] [Fig-1] [Fig.1] is a schematic side view representation of a mode of implementation of an electricity production device according to the invention at the end of the injection of liquids L1, L2 into their respective compartments during a given period,

[0053] [Fig.2] [Fig.2] is a schematic side view representation of an embodiment of an electricity production device according to the invention at the end of the injection of liquids L1, L2 into their respective compartment during a period following a period as illustrated in [Fig.1],

[0054] [Fig.3] [Fig.3] is a graphic illustrating the curves, obtained by chronovoltaic measurement, of the voltage Eioad across the terminals of the external resistance Rioad, in solid lines, for several potential differences Eo, in dashed lines, delivered by the generator during several successive periods,

[0055] [Fig.4] [Fig.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,

[0056] [Fig.5] [Fig.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,

[0057] [Fig. 6] [Fig. 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 generation device, denoted Pb_net, for several potential differences Eo delivered by the generator. generator,

[0058] [Fig.7] [Fig.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,

[0059] [Fig.8] [Fig.8] is a schematic side view representation of a improvement of the embodiment of the electricity production device according to the invention at the end of the injection of liquids L1, L2 into their respective compartments 31, 32 during a given period,

[0060] [Fig.9] [Fig.9] is a graph illustrating the net power density curve, noted Pb_net, as a function of Rioad obtained by the electricity production device according to the improvement illustrated on [Fig.8] for a potential difference Eo delivered by the generator of 0 mV. Description of the implementation methods

[0061] The embodiments described below are in no way limiting; variants of the invention may include, in particular, a selection of the described features, isolated from the other described features (even if this selection is isolated within a sentence containing these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one feature, preferably a functional one without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0062] With reference to Figures 1 and 2, an embodiment of the electricity production device 1 according to the invention is shown. 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 for at least the predetermined ion. The two compartments 31, 32 are intended to each receive a liquid L1, L2 having a different concentration of the predetermined ion. Cell 2 comprises two terminals 61, 62 respectively connected to the adsorption surfaces 41, 42 of the two compartments 31, 32. Cell 2 is capable of generating a potential difference Eocv between its two terminals 61, 62 in the presence of the respective liquids L1, L2 in the two compartments 31, 32. Device 1 comprises a voltage generator 7. The generator 7 comprises two terminals 71, 72.Terminal 71 of generator 7 is. connected to terminal 62 of cell 2 and the other terminal 72 of generator 7 constitutes a terminal 82 of device 1. The other terminal 81 of device 1 is constituted by the other terminal 61 of cell 2. Generator 7 is arranged to deliver a non-zero potential difference Eo between its two terminals 71, 72.

[0063] Cell 2 is a capacitive, salinity gradient type. Therefore, when cell 2 is in open circuit, bringing two liquids L1, L2, each containing a predetermined ion at a different concentration, into contact with the two respective adsorption surfaces 41, 42, for example, liquid L1 in contact with adsorption surface 41 and liquid L2 in contact with adsorption surface 42, will lead to the appearance of a potential difference across the terminals 61, 62 of cell 2. This is due to the selective diffusion of at least one ion through membrane 2, which generates a salinity difference between the two compartments 31, 32, and to a different variation in the potential of one electrode 41, 42 compared to the other 42, 41 due to the variation in the concentration of at least one ion in compartments 31, 32.Closing the circuit, that is, connecting terminals 61 and 62 of cell 2 to a resistor, will cause a current to flow through the resistor and a drop in the capacitive potential difference between the two adsorption surfaces 41 and 42, and therefore across cell 2. The generated current will thus decrease with the decrease in the potential difference across cell 2. At this point, when cell 2 is "discharged," the liquids L1 and L2 are withdrawn from their respective compartments 31 and 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 periodically recovered from cell 2 by successive injections and withdrawals of liquids L1 and L2 in compartments 31 and 32.In this application, the period T of cell 2 or device 1 is understood to be the time between two successive injections of liquids L1, L2 into compartments 31, 32; that is, the injection of liquid L1 into compartment 31 and the injection of liquid L2 into compartment 32 during a given period T, followed by the injection of liquid L1 into compartment 32 and the injection of liquid L2 into compartment 31 during a subsequent period T+1, and vice versa. Figure 1 shows the state of device 1 at the end of the injection of liquids L1, L2 into their respective compartments 31, 32 during a given period T. Figure 2 shows the state of device 1 at the end of the injection of liquids L1, L2 into their respective compartments 31, 32 during a subsequent period T+1.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.

[0064] According to the embodiment, means for supplying 9 compartments with Liquids L1, L2 are shown. However, these supply means 9 are known and are not part of device 1. Cell 2 is only suitable for cooperating with these supply means 9, which are intended to be mounted on cell 2. The supply means 9 comprise two circuits 91, 92 connecting compartments 31, 32 respectively to a switching means 93, for example a pneumatic valve 93, arranged to control the injection of liquids L1, L2 into one of the circuits 91, 92. The supply means 9 include a pump arranged to regulate and control the injection flow rate of liquids L1, L2 into circuits 91, 92.

[0065] According to a first, non-limiting embodiment, the solutions used to illustrate the operation and performance of device 1 according to the invention are aqueous solutions L1, L2 comprising sodium chloride (NaCl) at two different concentrations. The operation of device 1 is therefore based on a difference in concentration of a predetermined ion, either sodium ions (Na+) or chloride ions (Cl) according to the first embodiment, in the two liquids L1, L2. According to this first embodiment, in practice and the intended applications, the two liquids envisaged for use in salinity gradient capacitive cells are seawater and freshwater in order to exploit their difference in salinity. The membrane 5 is a cationic ion exchange membrane made of tetrafluoroethylene sulfonate, or NAFION™, model NAFION™ 117, sold by Chemours®, with a thickness of 183 µm in its dry form.The adsorption surfaces 41 and 42 are made of carbon felt, have a geometric surface area of ​​approximately 2.2 cm², and are separated by 1.5 mm. Two graphite current collectors are connected to the adsorption surfaces 41 and 42. Each compartment 31 and 32 has a volume of approximately 0.34 cm³. The carbon felt adsorption surfaces 41 and 42 act as capacitive electrodes. A 50:1 ratio of 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 and 32 is 10 mL / min according to the first embodiment. Figure 1 illustrates the beginning of a period T when the liquid L1 with the highest concentration is injected into compartment 31; the Na+ cations have not yet diffused through membrane 5. Figure 1Figure 2 illustrates the beginning of a period T when the liquid L1 with the highest concentration is injected into compartment 32; at this stage, the Na+ cations have not yet diffused through membrane 5. The dotted insets in Figures 1 and 2 represent the equivalent circuit of cell 2 during its discharge through the external resistance, denoted Rioad. The equivalent circuit of cell 2 includes an internal resistance Rceii and a capacitance Cceii. The potential difference Eceii across terminals 61, 62, of cell 2 is equal to the sum of the Donnan potentials generated by 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 abandonment potential, noted Eocv, of cell 2 is approximately equal to 144 millivolts (mV), the resistance Rceu of cell 2 is approximately equal to 5.39 ohms (Q) and the capacitance Cceii of cell 2 is approximately 1.27 Farads (F).

[0066] The graph in [Fig.3] shows the curves from the chronovoltaic measurements of the voltage Eioad across the terminals of the external resistance Rioad, in solid lines, for several potential differences Eo, in dashed lines, delivered by the generator 7, for a load resistance Rioad fixed at 75 Q and for several successive periods T of a duration of 45 seconds each.

[0067] 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 this 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 Ph-ei supplied by device 1 according to the invention is 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_riel is calculated as the difference between the power density dissipated by device 1 in the external resistance Rioad over the discharge time and the power density supplied by generator 7 over the discharge time. Surprisingly, for external resistance Rioad values ​​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 discharge and the power density supplied by generator 7 during discharge. Device 1 achieves a maximum net power density of 3.35 Wm², which corresponds to an increase of 45.4% compared to the maximum net power density achieved by cell 2.

[0068] 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 as a percentage and corresponds to the ratio between (i) the difference between the net power density Phei 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 = (Pnb - Pnb) / Pnb. The net power densities provided by device 1 and cell 2 have The values ​​were measured for several NaCl concentration differences in liquids L1 and L2 and for several time periods T. The net power density Pb-net provided by device 1 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, denoted Rmax, was used. The results presented in Table 1 were obtained with device 1 comprising a NAFION™ 117 membrane 5, those in Table 2 with device 1 comprising a Fumasep FKS-30 membrane 5 sold by Fumatech® with a thickness between 26 and 30 µm, and those in Table 3 with device 1 comprising a NAFION HP membrane 5 sold by Chemours® with a thickness of 22 µm.It is observed that regardless of the membrane 5 used, the performance of device 1 increases and then decreases when the period T exceeds 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 the ions in solution and of at least one ion, thickness of membrane 5, type of connectors, etc.). It is also noted that performance increases 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 performance of device 1.

[0069] [Tables 1] L1 L2 T (s) Eo (mV) Rmax (£2) Pb-net (W / m2) Gain (%) 5,13 0,17 30 0 10 2,9 0 200 30 2,3 -19,8 550 50 2,8 -4,1 800 75 3,2 11,6 45 0 12 2,3 0 200 30 3,1 34,8 550 50 3,3 45,4 800 75 3,8 63,7 60 0 15 1,9 0 200 30 2,9 48,9 550 62 3,2 61,5 800 75 3,2 62,6 5,13 0,017 45 0 12 3,6 0 200 20 3,7 4,3 550 75 4,3 20 800 100 4,3 20,4

[0070] [Tableaux2] L1 L2 T (s) Eo (mV) Rmax (£2) Pb-net (W / m2) Gain (%) 5,13 0,017 45 0 12 3,6 0 200 20 3,7 4,3 550 75 4,3 20 800 100 4,3 20,4

[0071] [Tableaux3] L1 5,13 L2 0,017 T (s) 45 Eo (mV) Rmax (£2) Pb-net (W / m2) Gain (%) 0 12 3,6 0 200 20 3,7 4,3 550 75 4,3 20 800 100 4,3 20,4

[0072] 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 Rioad, giving the optimal results and denoted Rmax, was used. Measurements were performed with each of the membranes 5: FKS-30, Nafion 117, and Nafion HP. For each Eo, a resistance range from 0.1 to 300 Ω was tested.

[0073] In the case of device 1 comprising the 5 FKS-30 membrane, the cell 2's dropout potential Eocv and cell resistance Rœu are 157 mV and 6.08 Ω, respectively. A net power density Ph„ei provided by device 1 is 4.01 W.m² for an optimal resistance Rmax of 75 Ω. The net power density Pb_net provided by device 1 corresponds to a 45% increase compared to the net power density Pnb of 2.75 Wm² provided by cell 2.

[0074] In the case of device 1 comprising the 5 Nafion HP membrane, the cell 2 dropout potential Eocv and cell 2 resistance Rceu are 158 mV and 4.92 Ω, respectively. These values ​​are slightly better than those exhibited by the 5 FKS-30 membrane and are significantly better than those of the Nafion 117, for which the cell 2 dropout potential Eocv is 145 mV and the cell 2 resistance Rceu varies between 5.4 and 6 Ω. For the 5 Nafion HP membrane, the best results are obtained for an optimal resistance Rmax of 50 Ω. A net power density Pb_net of 5.26 Wm² was provided by device 1, which corresponds to an increase of 59.8% compared to the net power density Pnb provided by cell 2.

[0075] The best results obtained for the device 1 comprising the 5 Nafion HP membrane are due to the high selectivity and low resistance of this membrane 5 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.

[0076] In 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. Therefore, the use of adsorption surfaces 41, 42 that are selective for cations or anions, for example, or even more advantageously for a predetermined type of cation or anion, for example sodium ions (Na+), would further increase the performance of device 1.

[0077] In a second, non-limiting embodiment, the solutions used to illustrate the operation and performance of device 1 according to the invention are an aqueous solution, for example L1, of sodium hydrogen carbonate NaHCO3 at a concentration of 1 mol / L at a pH of 7.9 and an aqueous solution, for example L2, of sodium carbonate Na2CO3 at a concentration of 0.5 mol / L at a pH of 11.64. Solutions L1 and L2 therefore have different concentrations of hydronium ions H3O+. The operation of device 1 is thus, as in the first embodiment, based on a difference in concentration of a predetermined ion, hydronium ions in the case of the second embodiment, in the two liquids L1 and L2.According to this second embodiment, in practice and the applications intended, it is envisaged to exploit CO2, for example CO2 emitted by gases produced during the combustion of fossil fuels or stale gases loaded with CO2 emitted by industrial, agri-food or agricultural activities. Also, according to the non-limiting embodiment, the pH difference is obtained by injecting CO2, by bubbling, into one of the compartments 31, 32 containing a solution of Na2CO3 and / or NaHCO3 so as to decrease the pH and induce a pH difference between the two compartments 31, 32. It is also possible to use other ion concentrations in solutions L1 and L2, other solutions L1 and L2 and / or other pairs of solutions L1 / L2 (inducing different pH 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 higher temperature than the other solution or by heating the compartment, for example 31, to increase the temperature of the solution, for example L1, that it contains.

[0078] According to the second embodiment, cell 2 and device 1 are structurally identical to those described for the first embodiment. The operation of cell 2 is identical and consists of periodically recovering a current by successive and alternating injections and withdrawals of liquids L1, L2 in compartments 31, 32. Also, the parameters and operating parameters of cell 2 and device 1 not described for the second embodiment are identical to those previously described. The adsorption surfaces 41 and 42 have a geometric area of ​​approximately 10.1 cm². The apparent surface area of ​​membrane 5 is approximately 5.5 cm². The thickness of membrane 5 is approximately 0.3 mm. The injection rate of liquids L1 and L2 into circuits 91 and 92 is approximately 15 mL / min. The volume of compartments 31 and 32 is approximately 0.165 cm³.

[0079] The porous membrane 5 used is a non-selective membrane 5, model Celgard 3501, sold by Celgard®, with a thickness of 25 µm in its dry form and a pore size of 0.064 µm. The injection flow rate of liquids L1, L2 into circuits 91, 92, i.e., the filling flow rate, is 15 mL / min according to the embodiment. The duration of the period T of such a cell 2 was observed to be 60 seconds.

[0080] The adsorption surfaces 41, 42 are made of composite material and have a geometric surface area of ​​approximately 10.15 cm². The composite material adsorption surfaces 41, 42 act as capacitive electrodes. According to a non-limiting embodiment, the composite material adsorption surfaces 41, 42 consist of carbon felt coated with particles having an average size of 200 µm. The particles comprise 70% by mass of manganese(IV) oxide or manganese dioxide (MnO₂), 20% by mass of carbon black, and 10% by mass of polyvinylidene fluoride. The particle mass charge is approximately 12.4 mg / cm².

[0081] With reference to [Fig. 6], the net power densities Pnb supplied by cell 2 alone, i.e., for a zero potential difference Eo, in other words, in the absence of generator 7, are illustrated, as well as 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 Rioad used. As with the first embodiment, we observe that device 1 provides net power densities Pb_net higher than the net power densities Pnb provided by cell 2 alone, regardless of the load resistance Rioad used and regardless of the potential difference Eo delivered by generator 7.

[0082] With reference to [Fig. 7], the net power densities Pnb supplied 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 Ph 'ei supplied by device 1 for potential differences Eo delivered by generator 7 of 300, 400, 500, 600, and 700 mV are illustrated. The pH gradient is 3.75. The net power densities Pnb supplied by cell 2 alone and the net power densities Ph 'ei supplied by device 1 are presented as a function of the load resistance Rioad used. The range of optimal resistances Rmax has been reported on [Fig.7] for each potential difference Eo delivered by the generator 7. As for [Fig.6] and for the first embodiment, it is observed that the device 1 provides net power densities Pb-net higher 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.

[0083] It should be noted that the Celgard 3501 membrane used in the second embodiment is a non-selective membrane. The use of such a non-selective membrane significantly reduces the performance of device 1. Therefore, the use of a selective membrane, for example a cation-selective membrane, even more preferably one that is selective for hydronium ions, such as a proton exchange membrane, or, for example, an anion-selective membrane, even more preferably one that is selective for hydroxide ions, would significantly increase the performance of device 1.

[0084] With reference to [Fig. 8], and in an improvement of device 1 according to the first embodiment, a device 1 is proposed 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. The generator 7 comprises two terminals 71, 72, one terminal 71 being connected to terminal 62 of cell 2, 21 and the other terminal 82 being connected to terminal 64 of cell 2, 22. The generator 7 is 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 device 1 is connected to terminal 62 of cell 2, 22 and to terminal 72 of generator 7. 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 all types of cell 2 and liquids L1, L2 according to the invention. Therefore, this improvement is also applicable, for example, to the second embodiment.

[0085] With reference to [Fig. 9], and according to the improvement of device 1 as illustrated in [Fig. 8], the net power density Pb_net of device 1 is shown as a function of the load resistance Rioad for a voltage Eo delivered by generator 7 of 0 mV. The potential difference Eocv 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 L1, L2 in the two compartments 31, 32 is 850 mV, i.e., 70 mV less than the sum of the potential differences Eocv measured at terminals 61, 62 and 63, 64 of the two cells 2, 21 and 2, 22 taken individually. Furthermore, the net power values ​​Pb_net of device 1 are approximately 10% lower than the sum of the net power values ​​Pb_net of the respective devices 1, each comprising a individual cell 2 among the two cells 2, 21, 22. This difference arises from the fact that the solutions L1, L2 entering their respective compartment 31, 32 of cell 2, 22 have their concentration slightly modified after passing through their respective compartments 31, 32 of cell 2, 21. Therefore, a simple modification of the feeding means 9 so that the liquids L1, L2 are injected in parallel directly into the compartments 31, 32 of cells 2, 21 and 2, 22 would avoid the observed loss.

[0086] For each embodiment, it is observed that increasing the potential difference Eo delivered by the generator 7 significantly improves the performance of device 1 compared to the performance of cell 2 alone. In particular, increasing the potential difference Eo delivered by the generator 7 significantly increases the usable load resistance Rioad. Therefore, 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 given type of liquid L1, L2 used, the potential difference Eo delivered by the generator 7 exhibits an optimal range depending on the load resistance Rioad used.

[0087] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

[0088] Thus, it is possible to combine the different variants and improvements of the embodiments described above.

[0089] Furthermore, the different features, forms, variants and embodiments of the invention can be associated with each other in various combinations insofar as they are not incompatible or mutually exclusive.

Claims

Demands

1. Electricity production device (1), said device (1), comprising: - a cell (2), said cell comprising two compartments (31, 32), each compartment comprising 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 (L1, L2) having a different concentration of the predetermined ion, 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 Eocv between its two terminals in the presence of the respective liquids in the two compartments, - a voltage generator (7), said 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, wherein the predetermined ion adsorption surfaces (41, 42) are liquid porous layers (L1, L2) intended to receive the two compartments (31, 32).

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

5. Device (1) according to the preceding claim, wherein 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, wherein the generator (7) is arranged to deliver a non-zero potential difference Eo that is less than the absolute value of a redox potential of the liquids (L1, L2) and / or the absolute value of a redox potential of at least one predetermined ion.

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

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

10. Device (1) according to the preceding claim, wherein the feeding 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, wherein 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) mounted in series.

13. A 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 predetermined ion concentration difference between two liquids (L1, L2) each contained in one of the two respective compartments; each compartment includes 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, apply, by means of a voltage generator (7), said 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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