Device for generating energy from salinity gradients via membranes based on cross-linked cellulose fibers

Abstract

The present invention relates to a device for generating electrical energy, comprising: a) a first reservoir A (20A) comprising an electrode (30A) in contact with an electrolyte solution having a concentration CA of a solute (22A) for receiving the electrolyte solution having a concentration CA; b) a second reservoir B (20B) comprising an electrode (30B) in contact with an electrolyte solution having a concentration CB of one of the same solutes (22B), where CB is lower than CA; c) a membrane (10) separating the two reservoirs, the membrane comprising pores that allow electrolyte to diffuse from reservoir A to reservoir B through the pores; and d) a device (32) capable of supplying electrical energy generated by a potential difference existing between the two electrodes, characterized in that the membrane comprises at least one layer made of a cellulosic material comprising a network of crosslinked cellulose nanofibers and / or microfibers.

Description

[Technical Field]

[0001] Salinity gradient energy generation is one of the most potential renewable energy sources globally. [Background technology]

[0002] Among the various techniques currently under consideration, the reverse electrodialysis (RED) method is based on the use of membranes whose fundamental property is the selective transport of ions according to the sign of their charge. RED devices typically consist of alternating ion-exchange membranes between which salt water and fresh water are alternately circulated. The alternating circulation of salt water and fresh water between these ion-exchange membranes (IEMs) allows an ion flux to be established at each IEM in the device. At the end of this stack of membranes, electrodes collect the current generated by the total ion flux.

[0003] One of the problems encountered with devices for generating electricity from salinity gradients, such as current-RED devices, is that the power generation capacity of these devices is very low, because the power generated by the current membrane per unit area of ​​the membrane (i.e., membrane power) is only a few W / m 2 This is due to the fact that it is a membrane.

[0004] In particular, IEMs conduct ionic currents poorly and have a significant ohmic contribution to electrodialysis reversal systems. Furthermore, the preparation of these membranes is very expensive, and for this reason, a large portion of the maintenance investment in membrane-based processes is dedicated to replenishing these membranes.

[0005] An approach to this problem is presented in the international application WO2014 / 060690 published on April 24, 2014. In this approach, nanoporous membranes are proposed, the inner surfaces of whose pores are covered with boron nitride or more generally with a mixture of elements such as boron, carbon and nitrogen. These nanoporous membranes utilize the diffusion-percolation phenomenon within the pores, and can achieve a high energy density of kW / m 2 More recently, the inner surfaces of the pores have been coated with titanium oxide, generating a membrane power of 5 kW / m2 Nanoporous membranes that allow reaching membrane powers of this order are provided in the international application WO2017 / 037213 published on March 9, 2017. However, this approach involves the use of membranes based on boron nitride or titanium oxide, the preparation of which on a larger scale than laboratory scale is complex and prohibitively expensive, given the materials required. Furthermore, the materials used in these membranes are potentially hazardous and pose a risk if released into the environment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2014 / 060690 issue [Patent Document 2] WO2017 / 037213 issue Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, taking the above into consideration, it is possible to generate non-polluting, economical electrical energy, with a kW / m per square meter of membrane. 2 There is a need for a device that makes it possible to obtain a degree of energy production. [Means for solving the problem]

[0008] A device for generating electrical energy from a salinity gradient, comprising a membrane comprising a layer formed of a network of cellulose nanofibers and / or microfibers, has a kW / m per square meter of membrane. 2 The inventors have discovered that this makes it possible to obtain a degree of energy production.

[0009] The use of such membranes also makes it possible to facilitate the development of larger scale devices for the production of energy from salinity gradients and to reduce their costs.

[0010] It is therefore an object of the present invention to provide a device for generating energy using membranes with salinity gradients that are capable of generating high membrane power and that are economical, easy to prepare and have limited environmental hazards. DETAILED DESCRIPTION OF THE INVENTION

[0011] device The first object of the present invention is to 1. A device for generating electrical energy, comprising: - concentration of solute C A The purpose is to receive an electrolyte (22A) having a concentration C A a first reservoir A (20A) containing an electrode (30A) in contact with an electrolyte solution having - Concentration C of the same solute B C B C A Lower, concentration C B a second reservoir B (20B) containing an electrode (30B) in contact with an electrolyte having - a membrane (10) separating the two reservoirs, the membrane comprising pores that allow electrolyte to diffuse through said pores from reservoir A to reservoir B; and - A device that allows the supply of electrical energy generated by the potential difference existing between two electrodes (32) wherein the membrane comprises at least one layer formed of a cellulosic material comprising a network of cross-linked cellulose nanofibers and / or microfibers.

[0012] The electrical energy generating device according to the present invention comprises two reservoirs (reservoir A (20A) and reservoir B (20B) respectively) separated by a membrane 10. Each of the two reservoirs A and B contains the same solute at a respective concentration C A and C BThe electrodes 30A and 30B are immersed in an electrolyte solution (22A, 22B) intended to receive the electrolyte solution (22A, 22B). The two electrodes (30A, 30B) are connected to a device that allows the capture and then delivery of the generated electrical energy.

[0013] To generate ion flux through the membrane, the concentration C of the same solute in the electrolyte (22A, 22B) A and C B is always different.

[0014] In the context of the present invention, C B is C A lower, which is arbitrarily considered to result in the cycling of solute ions from reservoir A to reservoir B.

[0015] The membrane (10) separating the two reservoirs A and B contains pores that allow electrolyte to diffuse through the pores from reservoir A to reservoir B. Diffusion occurs from reservoir A to reservoir B. The pores have an average cross-sectional area that allows both water molecules and solute ions to circulate.

[0016] The thickness of the membrane is advantageously between 2 μm and 100 μm, preferably between 2 μm and 75 μm.

[0017] The membrane is advantageously a membrane 1 m 2 10-20g of cellulosic material per 1m of membrane, preferably 2 Contains 15-20g of cellulosic material per serving.

[0018] The electrodes (30A, 30B) can be partially or completely immersed in the electrolyte (22A, 22B). It is also possible to provide a configuration in which the electrodes are at least part of the wall of the reservoir.

[0019] The device 32 allows for the capture and then delivery of electrical energy naturally generated by the potential difference that exists between the two electrodes 30A and 30B. The device 32 can consist of a simple cable connected to a battery, bulb, or any other form of electrical demand.

[0020] In the device according to the invention, the electrical energy causes the migration of the electrolyte, more particularly of the ions generated from said electrolyte, through the pores of the material of the membrane, from the most concentrated solution to the less concentrated solution under the influence of their surface properties, in particular their surface charge, of the same solute of the electrolyte, C A and C B is generated thanks to the difference between

[0021] The inventors have shown, completely unexpectedly, that nanofiber and / or cellulose-based membranes can achieve a current density of several hundred W / m under the action of a salinity gradient. 2 We discovered that it can generate extremely high membrane power of about 1000kJ / cm.

[0022] Without wishing to be bound by any particular theory, the inventors believe that the unexpected membrane power is determined by the surface charge of the nanofibers and / or cellulose and the geometry of the network they form, which allows for very good selective ion conductance through the membrane.

[0023] In particular, the inventors further demonstrate that the porosity and surface charge within the cellulose nanofiber and / or microfiber network unexpectedly influences the selective passage of ions through the membrane, thereby enabling the membrane to generate unexpected membrane power.

[0024] The surface charge density of the walls inside the pores of the membrane is advantageously between 0.001 and 3 C / m 2 Between 0.1 and 1 C / m 2 It is between.

[0025] The surface charge density of the film can be measured dosimetry.

[0026] Cellulose nanofibers and / or microfibers According to the present invention, the term "crosslinked" in reference to cellulose nanofibers and / or microfibers means that the fibers are connected to each other by covalent chemical bonds (sometimes called "bridges") to form a three-dimensional network in the cellulosic matrix form, in other words, they are not merely aggregated or self-assembled through weak bonds.

[0027] The covalent chemical bonds involved in the cross-linking of the cellulose nanofibers and / or microfibers can also carry charged groups and / or groups that become charged in the presence of water, such as when the cross-linking agent used is citric acid, in which case the cross-linking chemical bonds play a role in both the structure and surface charge of the outer layers (101, 103).

[0028] The network of cellulose nanofibers and / or microfibers advantageously has pores with diameters between 10 and 1000 nm.

[0029] According to the present invention, the expression cellulose "nanofiber" refers to a cellulose-based three-dimensional object having two of its three external dimensions in the nanometer scale (i.e., two of its three dimensions in the range of 1 to 100 nm) and a third external dimension that is significantly larger than the other two, but not necessarily in the nanometer scale.

[0030] The cellulose nanofibers advantageously have a diameter in the range of 1 to 100 nm, preferably in the range of 1 to 70 nm, more preferably in the range of 4 to 30 nm, and particularly in the range of 4 to 20 nm, and their length is advantageously between 0.5 and 100 μm, particularly between 0.5 and 50 μm, for example between 0.5 and 10 μm, and for example further between 0.5 and 2 μm.

[0031] According to the present invention, the expression cellulose "microfiber" refers to a three-dimensional object having two of its three external dimensions in the micrometer scale (i.e., two of the three dimensions in the range of 0.1 to 1 μm) and having a third external dimension significantly larger than the other two dimensions.

[0032] The cellulose microfibers advantageously have a diameter in the range of 100 to 1000 nm, preferably in the range of 100 to 700 nm, more preferably in the range of 100 to 200 nm, and furthermore, their length is advantageously between 0.5 and 100 μm, in particular between 1 and 50 μm, for example between 1 and 10 μm, and even more preferably between 1 and 5 μm.

[0033] The cellulose nanofibers and / or microfibers advantageously have a shape factor of greater than 30, preferably greater than 100.

[0034] Advantageously, the cellulosic material comprises at least 90% by weight cellulose nanofibers and / or microfibers, at least 95% by weight cellulose nanofibers and / or microfibers, more preferably even at least 99% cellulose nanofibers and / or microfibers, based on the weight of the cellulosic material.

[0035] Cellulose nanofibers and / or microfibers can be obtained by techniques known to those skilled in the art, in particular by mechanical, enzymatic or chemical treatment of lignocellulosic materials of natural origin, such as wood.

[0036] In the case of wood, these treatments have the specific effect of separating cellulose from other wood constituents, such as lignin and hemicellulose. To this end, natural cellulose fibers are pre- or post-treated chemically, especially enzymatically, and / or mechanically to initiate structural disruption before mechanical treatment in a homogenizer. It is known that the size and especially the diameter of the cellulose fibers of such materials can be modulated depending on the treatments applied to the natural cellulose source.

[0037] Thus, cellulose nanofibers and / or microfibers can be obtained by mechanical treatment of wood fibers, which provides sufficient mechanical energy to burst the fibers of native cellulose by at least partially breaking the hydrogen bonds that hold the microfibrils together. Mechanical treatment is often followed by a chemical or enzymatic treatment step. For example, this treatment step can be an oxidation treatment, particularly an oxidation treatment using an oxidizing agent such as TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxy). The resulting products are often referred to in the literature as "nanofibrillated cellulose" (abbreviated as "NFC"), "cellulose nanofiber" (abbreviated as "CNF"), or "microfibrillated cellulose" (abbreviated as "MFC").

[0038] Generally, MFC materials are prepared from mechanical and / or chemical processes on a smaller scale than those used to obtain NFC, and have fibers with larger diameters than those typically observed in NFC. However, there are no clear definitions of MFC and NFC / CNF, and thus the terms are often used interchangeably in the literature.

[0039] The cellulose nanofibers and / or microfibers are preferably nanocellulose nanofibers and / or microfibers.

[0040] The cellulosic material may in particular comprise up to 5% by weight hemicellulose, more preferably up to 3% by weight hemicellulose, otherwise up to 1% by weight hemicellulose.

[0041] The cellulosic material may in particular comprise at most 5% by weight lignin, more preferably at most 3% by weight lignin, otherwise at most 1% by weight lignin.

[0042] Due to the fact that cellulose monomers naturally carry alcohol groups at their C2, C3 or C6 carbon atoms, the cellulose nanofibers and / or microfibers of the present invention inherently carry a negative surface charge.

[0043] In one embodiment, the intrinsic negative surface charge of the cellulose nanofibers and / or microfibers of the present invention can be increased by functionalizing them with negatively charged groups and / or groups that become negatively charged in the presence of water. This embodiment is particularly advantageous when the charged groups and / or groups that become negatively charged in the presence of water of the functionalized nanoparticles of the inner layer (102) have a negative sign. In fact, this has the advantage of increasing the surface charge of the entire composite membrane of the present invention.

[0044] The charged groups carried by the microfibers and / or nanofibers and / or groups that become charged in the presence of water are advantageously chemically bound in a covalent manner to the surface of said cellulose microfibers and / or nanofibers.

[0045] Any charged group known to those skilled in the art that allows an increase in the charge density of the microfibers and / or cellulose nanofibers of the present invention and / or groups of the latter that become charged in the presence of water can be used within the scope of the present invention.

[0046] Advantageously, the charged groups carried by the cellulose nanofibers and / or microfibers and / or groups that become charged in the presence of negatively charged water are sulfonate groups -SO3 - , carboxyl group -CO2 - , carboxyalkyl group R-CO2 - (R is C1-C4, preferably C1 alkyl), an aminodiacetate group -N(CH2CO2 - )2, phosphonate group PO3 2- Amidoxime group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , a thiol group -SH, and mixtures thereof.

[0047] Carboxyl group - CO2 - and carboxyalkyl groups R-CO2 - (R is C1 to C4, preferably C1 alkyl).

[0048] Therefore, -CO2 - Cellulose nanofibers and / or microfibers bearing carboxyl groups (i.e., oxidized cellulose nanofibers and / or microfibers) can be obtained, for example, by oxidation of cellulose nanofibers and / or microfibers, for example, by TEMPO oxidation, where oxidation occurs preferentially on the primary alcohol groups carried by the C6 carbon atoms of the cellulose nanofiber and / or microfiber monomers.

[0049] Carboxyalkyl group R-CO2 - Cellulose nanofibers and / or microfibers bearing the formula (i.e., carboxyl-alkylated cellulose nanofibers and / or microfibers) can be obtained, for example, by etherification of cellulose nanofibers and / or microfibers. The etherification occurs preferentially on alcohol groups carried by the C2, C3, or C6 carbon atoms of the monomers of the cellulose nanofibers and / or microfibers.

[0050] In another embodiment, the intrinsic negative surface charge of the cellulose nanofibers and / or microfibers of the present invention can be reversed by functionalizing them with positively charged groups and / or groups that become charged in the presence of water.

[0051] This embodiment is preferred if the charged groups of the functionalized nanoparticles of the inner layer (102) and / or the groups that become charged in the presence of water have a positive sign.

[0052] Any charged group and / or group that becomes charged in the presence of water and that is known to those skilled in the art and that makes it possible to impart a positive surface charge onto the cellulose nanofibers and / or microfibers can be used in the context of the present invention.

[0053] Advantageously, the positively charged groups and / or groups that become positively charged in the presence of water are quaternary ammonium groups -N(R)3 + (wherein R is a C1-C4 alkyl), a tertiary ammonium group -N(H)R)2 + (R is a C1-C4 alkyl, preferably a C1 alkyl), a dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 + and mixtures thereof.

[0054] Quaternary ammonium groups are preferred.

[0055] Single layer membrane In a first embodiment, the invention relates to a device according to the invention, the membrane of which comprises a monolayer (101) made of a cellulosic material as defined above.

[0056] The inventors have surprisingly shown that membranes comprising a monolayer (101) formed of a network of cross-linked cellulose nanofibers and / or microfibers surprisingly enable the generation of higher membrane power compared to prior art membranes and are suitable for industrial development.

[0057] The thickness of the membrane comprising the monolayer (101) is advantageously between 2 μm and 50 μm, preferably between 5 μm and 20 μm, more preferably between 10 μm and 20 μm.

[0058] In the present invention, the thickness of the film and the thickness of the different layers are measured by scanning electron microscopy of cross-sections of the dry film.

[0059] Methods for preparing monolayer films The membrane containing the monolayer is i) filtering a solution comprising cellulose nanofibers and / or microfibers onto a filtering support to form a layer comprising nanofibers and / or microfibers; ii) filtering a cross-linking solution capable of cross-linking the cellulose nanofibers and / or microfibers of the layer obtained in step i); iii) drying the product of step ii), preferably in an oven; iv) Removing the filtration support to obtain a membrane comprising the layer. It can be easily prepared by a method comprising:

[0060] The method is simple, easy to implement, economical, and allows for control of the thickness of each layer of the composite membrane.

[0061] The cellulose nanofibers and / or microfibers used in the method are as defined in the first object of the present invention.

[0062] The filtration of steps i) and ii) is advantageously carried out using a vacuum pump, preferably under a vacuum of 1 bar.

[0063] The solution of cellulose nanofibers and / or microfibers contains 0.1% by weight to 1% by weight of cellulose nanofibers and / or microfibers, preferably 0.3% by weight to 0.6% by weight of cellulose nanofibers and / or microfibers.

[0064] The nanofibers and / or microfibers of the solution of step i) may be functionalized as detailed in the first object of the present invention.

[0065] The cross-linking solution introduced in step ii) advantageously comprises between 0.005M and 0.02M of one or more cross-linking agents, preferably between 0.008M and 0.012M of one or more cross-linking agents.

[0066] As detailed above, the cross-linking agent preferentially retains charged groups and / or groups that become charged in the presence of water.

[0067] Any other technique known to those skilled in the art, whether discontinuous (i.e., batchwise) or continuous, may be considered, for example the so-called "roll-to-roll" technique, in which the membrane is produced continuously and then stored in the form of a roll.

[0068] composite membrane In a second embodiment, the device comprises a composite membrane comprising two outer layers (101, 103), each made of a cellulosic material as defined above, between which is disposed an inner layer (102) made of a second material comprising nanoparticles functionalized with charged groups and / or groups that become charged in the presence of water.

[0069] The second material advantageously has pores with a diameter between 10 and 100 nm.

[0070] The inventors have unexpectedly discovered that such a composite membrane generates a membrane power significantly higher than that of a membrane comprising a monolayer (101) as defined above.

[0071] Without being bound to a particular theory, the inventors believe that this improvement in membrane power is due to a synergistic effect between the properties of the network of cellulose nanofibers and / or microfibers, on the one hand, and the properties of the layer of nanoparticles functionalized with charged groups, on the other hand. The thickness of the composite membrane is advantageously preferably between 4 μm and 100 μm, more preferably between 4 μm and 75 μm.

[0072] The thickness of each of the outer layers (101, 103) is advantageously between 2 μm and 45 μm, preferably between 2 μm and 30 μm. The outer layers advantageously have the same thickness. In contrast, the thickness of the inner layer (102) is advantageously between 10 nm and 2 μm, between 10 nm and 1 μm, between 10 nm and 800 nm, preferably between 10 nm and 400 nm, preferably between 200 nm and 500 nm.

[0073] Preferably, the thickness of each of the outer layers (101, 103) is advantageously between 2 μm and 25 μm, and the thickness of the inner layer (102) is between 10 nm and 2 μm.

[0074] According to the inventors, the extremely small thickness of the inner layer (102) makes it possible to obtain excellent permeability while significantly increasing the selective conductivity of ions.

[0075] Preferably, the membrane comprises less than 10 wt. % of the second material relative to the weight of the cellulosic material, preferably between 2 wt. % and 8 wt. % of the second material relative to the weight of the cellulosic material, more preferably between 3 wt. % and 5 wt. % of the second material relative to the weight of the first material.

[0076] In this embodiment, the cellulosic material of the outer layers (101, 103) ensures the integrity of the inner layer (102), particularly during its use, when the latter is subjected to stresses such as pressure gradients on either side of the membrane.

[0077] Preferably, the nanofibers and / or microfibers of the outer layer (101, 103) carry charged groups or groups that become charged in the presence of water, said groups advantageously having a charge of the same sign as the charged groups or groups that become charged in the presence of water of the functionalized nanoparticles of the inner layer (102).

[0078] This has the advantage of increasing the surface charge of the entire film.

[0079] According to the inventors, the presence of these charged groups with the same sign in the inner (102) and outer (101, 103) layers of the membrane, or groups that become charged in the presence of water, makes it possible to obtain a synergistic effect, i.e., an unexpected improvement in the ion-selective conductance through the membrane.

[0080] Thus, in this embodiment, the cellulosic material plays a role in the structure of the membrane and its ability to ensure ion-selective conductivity.

[0081] Furthermore, the covalent chemical bonds involved in cross-linking the nanofibers and / or microfibers can also carry charged groups and / or groups that become charged in the presence of water, such as when the cross-linking agent used is citric acid, in which case the cross-linking chemical bonds play a role in both the structure and surface charge of the outer layers (101, 103).

[0082] Functionalized nanoparticles According to the present invention, the term "nanoparticle" means a three-dimensional object having at least one external dimension lying on the nanometer scale (ie at least one dimension ranging between 1 and 100 nm).

[0083] The second material advantageously comprises nanoparticles in the form of individual nanoparticles, ie not agglomerated, or in other words covalently bonded to one another.

[0084] The second material advantageously comprises at least 50% by weight nanoparticles, at least 95% by weight nanoparticles, more preferably at least 99% by weight nanoparticles, relative to the weight of the second material.

[0085] Advantageously, the nanoparticles are not in the form of nanotubes.

[0086] The nanoparticles are preferably lamellar nanoparticles.

[0087] According to the present invention, the term "lamellar nanoparticles" refers to nanoparticles comprising atoms in the form of a monolayer of atoms that are covalently bonded together. Lamellar nanoparticles can consist of a single monolayer of atoms (2D materials) or a stack of 2 to 5 monolayers of atoms that are held together by weak bonds, e.g., van der Waals forces.

[0088] In other words, a lamellar nanoparticle is a three-dimensional object with a first external dimension on the nanometer scale and two other dimensions significantly larger than the first, specifically varying between the nanometer and micrometer scales.

[0089] The lamellar nanoparticles have a median diameter (also designated by the acronym "D50") that is preferably comprised between 5 μm and 50 μm, preferably between 10 μm and 20 μm, more preferably 15 μm.

[0090] According to the present invention, the terms "monolayer," "bilayer," and "few-layer" in reference to lamellar nanoparticles refer to lamellar nanoparticles consisting of a monolayer of atoms, two monolayers of atoms, and 3-5 monolayers of atoms, respectively. Bilayer and few-layer lamellar nanoparticles are typically stabilized by weak interactions between the monolayers of atoms, e.g., van der Waals interactions.

[0091] The lamellar nanoparticles are preferably lamellar nanoparticles of metal oxides, in particular lamellar nanoparticles of SnO2 or TiO2, lamellar nanoparticles of transition metal dichalcogenides, for example lamellar nanoparticles of molybdenum disulfide MoS2, lamellar nanoparticles of carbon, or mixtures thereof.

[0092] The lamellar carbon nanoparticles are preferably lamellar nanoparticles of single-layer graphene, lamellar nanoparticles of two-layer graphene, lamellar nanoparticles of few-layer graphene or mixtures thereof.

[0093] Single-layer graphene nanoparticles are preferred.

[0094] According to the present invention, monolayer graphene is a two-dimensional crystalline material composed of a specific allotropic form of carbon, which can be represented as a flat honeycomb. More specifically, monolayer graphene is composed of a single sp 2 It is a sheet of hybridized carbon atoms in a plane, and therefore can be described as a monolayer.

[0095] According to the present invention, bilayer graphene (or BLG) is a material consisting of a stack of two monolayers of graphene stabilized by van der Waals interactions between the two monolayers of graphene. BLG can be obtained by exfoliation of graphite or by chemical vapor deposition (CVD).

[0096] According to the present invention, few-layer graphene (or FLG) is a material consisting of a stack of 3 to 5 sheets of graphene stabilized by van der Waals type interactions between the different graphene planes.

[0097] The lamellar carbon nanoparticles are preferably lamellar nanoparticles of monolayer molybdenum disulfide, bilayer molybdenum disulfide, few-layer molybdenum disulfide or mixtures thereof.

[0098] Depending on the sign of these charges, the charged groups or groups that become charged in the presence of water will impart a negative or positive surface charge on the inner layer (102) of the composite membrane when placed in the presence of water.

[0099] Any charged group known to those skilled in the art or a group that becomes charged in the presence of water and that allows an increase in the surface charge of the graphene particles can be used in the context of the present invention.

[0100] In one embodiment, the nanoparticles are surface functionalized with negatively charged groups and / or groups that become negatively charged in the presence of water.

[0101] Negatively charged groups and / or groups that become negatively charged in the presence of water include epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, sulfonate groups -SO3 - , carboxyalkyl group R-CO2 - (R is C1-C4, preferably C1 alkyl), an aminodiacetate group -N(CH2CO2 - )2, phosphonate group PO3 2- Amidoxime group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , a thiol group -SH, and mixtures thereof.

[0102] Preferably, the nanoparticles whose surfaces are functionalized with negatively charged groups or groups that become negatively charged in the presence of water are lamellar nanoparticles of graphene oxide (or GO).

[0103] The lamellar graphene oxide nanoparticles have negatively charged groups or groups that become negatively charged in the presence of water, which groups are advantageously selected from epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, and mixtures thereof.

[0104] In one embodiment, the nanoparticles are surface functionalized with positively charged groups and / or groups that become positively charged in the presence of water.

[0105] Advantageously, the positively charged groups and / or groups that become positively charged in the presence of water are quaternary ammonium groups -N(R)3 + (wherein R is a C1-C4 alkyl), a tertiary ammonium group -N(H)R)2 + (R is a C1-C4 alkyl, preferably a C1 alkyl), a dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 + and mixtures thereof.

[0106] Method for preparing composite membranes The composite membrane according to the second embodiment comprises: i) filtering a solution comprising cellulose nanofibers and / or microfibers on a filtration medium to form a first outer layer (101) comprising cellulose nanofibers and / or microfibers; ii) filtering the solution of functionalized nanoparticle particles onto the outer layer (101) obtained at the end of step i) to form an inner layer (102) on said first outer layer (101); iii) filtering the solution of cellulose nanofibers and / or microfibers to form a second outer layer (103) comprising nanofibers and / or microfibers on the inner layer (102) obtained at the end of step ii); iv) filtering a cross-linking solution capable of cross-linking the cellulose nanofibers and / or microfibers of the outer layers (101, 103); v) drying the product of iv) in an oven; vi) removing the filtration support to obtain the composite membrane It can be prepared by a method comprising the steps of:

[0107] Cellulose nanofibers and / or microfibers and nanoparticles functionalized on the surface with charged groups and / or groups that become charged in the presence of water are as defined in the first object of the present invention.

[0108] The method is simple, easy to implement, economical, and allows for control of the thickness of each layer of the composite membrane.

[0109] The filtrations of steps i), ii), iii) and iv) are advantageously carried out using a vacuum pump, preferably under a vacuum of 1 bar.

[0110] The filtration of step i) may optionally be followed by a step i1) consisting of filtering the crosslinking solution on the outer layer obtained at the end of step i).

[0111] The filtration of step ii) may optionally be followed by step ii1) consisting of filtering the cross-linking solution on the inner layer (102) obtained at the end of step ii).

[0112] The solution of nanofibers and / or microfibers introduced in steps i) and iii) contains 0.1% to 1% by weight of cellulose nanofibers and / or microfibers, preferably 0.3% to 0.6% by weight of cellulose nanofibers and / or microfibers.

[0113] The nanofibers and / or microfibers of the solution of steps i) and iii) may be functionalized as detailed in the first object of the present invention.

[0114] The solution of functionalized nanoparticles introduced in step ii) contains 0.001% to 0.01% by weight of nanoparticles, preferably 0.003% to 0.006% by weight of functionalized nanoparticles.

[0115] The cross-linking solution introduced in step iv) advantageously comprises between 0.005M and 0.02M of one or more cross-linking agents, preferably between 0.008M and 0.012M of one or more cross-linking agents.

[0116] The drying of step v) is advantageously carried out at a temperature that allows the crosslinking reaction to occur and below a temperature that would damage the fibers and / or nanofibers. Preferably, the drying is carried out at a temperature comprised between 80°C and 150°C, in particular between 80°C and 120°C, more preferably still between 80°C and 100°C.

[0117] As detailed above, the cross-linking agent preferentially retains charged groups and / or groups that become charged in the presence of water.

[0118] Any other technique known to those skilled in the art may be considered, whether discontinuous (i.e., batchwise) or continuous, for example the so-called "roll-to-roll" technique, in which the membrane is produced continuously and then stored in the form of a roll.

[0119] Other components of the device Reservoirs A and B of the device according to the invention contain the same solute at respective concentrations C A and C B Each of the electrolytes (22A, 22B) contains an electrolyte having B is C A Lower.

[0120] Each reservoir A and B can be any device or natural environment, open or closed, capable of containing a liquid.

[0121] By placing electrolytes of different concentrations in the two reservoirs A and B, an osmotic flow occurs between the two reservoirs, preferably by diffusiosmosis, i.e., without the appearance of any osmotic pressure. In another embodiment, a concentration gradient could also be obtained by a temperature gradient between the two reservoirs, by acting on the solubility of the salt as a function of temperature.

[0122] In the context of the present invention, the concentration ratio Rc (Rc is equal to the ratio of the concentration of the most concentrated solution / the concentration of the least concentrated solution) is 1 to 10 9 Preferably, the concentration ratio C A / C B is greater than 1 and 10 9 less than or equal to 10 and advantageously greater than 10 5 The following is the result.

[0123] An electrolyte is an aqueous solution containing electrolytes. Electrolytes can be of any chemical nature, as long as they are dissolved in solution in the form of charged ions. Preferably, these ions come from dissolved salts, such as NaCl, KCl, CaCl, and MgCl. Electrolytes can be: - synthetic solutions; - Natural solutions, such as fresh water from lakes or rivers, groundwater, brackish water, seawater; - Industrially produced water, oil produced water or biological solutions.

[0124] Preferably, the electrolyte is an aqueous solution containing a solute selected from alkali or alkaline earth halides, preferably selected from NaCl, KCl, CaCl2 and MgCl2, more preferably the solute is NaCl.

[0125] To improve the osmotic flow generated on either side of the membrane according to the invention, the pH of the solution can be adjusted according to the isoelectric point of the material that makes up the membrane.

[0126] In the context of the present invention, pH iso means the pH of the isoelectric point of the material that makes up the membrane. iso is determined by methods known to those skilled in the art, in particular by potentiometric acid / base titration methods.

[0127] Even more advantageously, a pH gradient can be established between the two reservoirs, with the pH difference between the two solutions being greater than 1, preferably greater than 2, to increase the asymmetry of the device and amplify the amount of electrical energy generated by the device.

[0128] Each of reservoirs A and B of the device according to the present invention also contains an electrode (30A, 30B) positioned to contact the electrolyte (22A, 22B).

[0129] Different types of electrodes can be used to collect the potential or current that develops between the two reservoirs.

[0130] Na + or Cl - Any type of electrode capable of collecting the flux of ions, preferably silver and silver chloride (Ag / AgCl), carbon and platinum (C / Pt), carbon (C), graphite or iron [Fe(CN)6] 4- / [Fe(CN)6] 3- Electrodes composed of composites of the type can be used.

[0131] The electrodes may be partially or completely immersed in the electrolyte, or may be provided in the form of at least a portion of the wall of the reservoir.

[0132] The electrodes can in particular be circulating electrodes ("redox flow"), the principle of which is based on an oxidation reaction and a reduction reaction at each of the electrodes.

[0133] The electrodes are preferably capacitive or supercapacitive electrodes, the principle of which is based on the interaction of the electrode and the electrolyte leading to the spontaneous appearance of an accumulation of charge at the interface.

[0134] These electrodes are connected together in a device 32, allowing the capture and then supply of electrical energy naturally generated by the potential difference that exists between them. These electrodes can be connected in particular by a simple cable that connects to a battery, a bulb, or any other form of electrical demand.

[0135] The device thus described makes it possible to harvest electrical energy generated from the flux of charged ions across a nanofluidic membrane.

[0136] In a particular embodiment of the invention, the device may comprise N reservoirs (20) and N-1 membranes (10), where N is an integer, in particular an integer between 3 and 100, in particular between 3 and 50.

[0137] In this device, the reservoirs and membranes are as defined above, and the assembly therefore consists of alternating reservoirs containing alternating concentrated and less concentrated electrolytes separated from each other by membranes.

[0138] Electrical Energy Production Method A second object of the present invention is a method for generating electrical energy using a device according to the first object of the present invention, comprising the following steps: i) A solute having a solute concentration C is placed in reservoir A (20A) so that the electrode (30A) provided in reservoir A comes into contact with the solution (22A). A supplying an electrolytic solution (22A) having ii) A solution of the same solute at a concentration C is added to reservoir B (20B) so that the electrode (30B) provided in reservoir B comes into contact with the solution (22B). B A step of supplying an electrolytic solution (22B) having C B C A Lower, process, iii) allowing the electrolyte to diffuse from reservoir A to reservoir B through membrane (10); iv) using the device (32) to capture the electrical energy generated by the potential difference existing between the two electrodes; The method includes:

[0139] Steps i) and ii) are carried out at a concentration C A Electrolyte solution with concentration C B This is preferably done by supplying in the form of a continuous flow an electrolyte having

[0140] More generally, these different steps are easily carried out by those skilled in the art using their general knowledge. [Brief explanation of the drawings]

[0141] [Figure 1] 1 shows a schematic diagram of an example of an electrical energy generating device according to the present invention, comprising two reservoirs 20A and 20B (reservoir A and reservoir B, respectively) separated by a membrane 10. Each of the two reservoirs contains an electrolyte solution 22A and 22B having respective concentrations CA and CB of the same solute, in which electrodes 30A and 30B are immersed. The two electrodes 30A and 30B are connected to a device that allows for the capture and subsequent delivery of the generated electrical energy. Each reservoir A and B can be any device or natural environment, open or closed, capable of containing a liquid. To generate ion flux through the membrane, the concentrations CA and CB of the same solute in the electrolyte solutions 22A and 22B must be different. In the context of the present invention, CB is arbitrarily considered to be lower than CA, which causes ionic circulation of the solute from reservoir A to reservoir B. The membrane 10 separating the two reservoirs A and B contains pores that allow the electrolyte to diffuse from reservoir A to reservoir B. Diffusion occurs from reservoir A to reservoir B. The pores have an average cross-sectional area that allows both water molecules and solute ions to circulate. The electrodes 30A and 30B can be partially or completely immersed in the solutions 22A and 22B. It is also possible to provide a configuration in which the electrodes are at least part of the walls of the reservoirs. The device 32 allows for the capture and then supply of electrical energy that is naturally generated by the potential difference that exists between the two electrodes 30A and 30B. The device can consist of a battery, a bulb, or a simple cable connected to any other form of electrical supply. [Figure 2] 1 shows a schematic cross-sectional view of an example of a membrane (10) according to the invention comprising a monolayer (101) formed of a cellulosic material comprising nanofibers and / or cross-linked cellulose microfibers. [Figure 3] An example of a membrane (10) according to the invention is shown schematically in cross section, in which the membrane is a composite membrane comprising two outer layers (101, 103), each made of a cellulosic material containing crosslinked cellulose nanofibers and / or microfibers, between which is disposed an inner layer (102) made of a material containing nanoparticles whose surface is functionalized with charged groups and / or groups that become charged in the presence of water. [Example]

[0142] The invention will be better understood on reading the following examples which illustrate the invention without limiting it.

[0143] Example 1 Preparation of monolayer membranes and measurement of membrane power of monolayer membranes Equipment and raw materials The materials used are listed below: - Buchner filter - 1 bar vacuum pump - 0.1μm PVDF filter paper - Reinforced oven

[0144] The raw materials used in this example are listed below: - cellulose nanofibers negatively charged by carboxymethylation or TEMPO oxidation; - Citric acid, 99% by volume.

[0145] Preparation of monolayer membranes The preparation method used was as follows: · 3.5 ml of nanocellulose solution is filtered through a PVDF filter onto a Buchner filter. The vacuum pump is set to a vacuum of 1 bar; · Once all the solution has been filtered, filter 10 ml of citric acid solution over it (acts as a cross-linking agent between the nanofibers); Once all the filtered citric acid solution has been pumped, open the Büchner device and remove the filter paper with the filtrate.

[0146] The assembly of filtrate and filter paper is then placed in a laboratory oven at 85°C for 15 minutes (drying and cross-linking reaction).

[0147] Finally, the membrane is separated from its filtration medium, possibly having been soaked beforehand in an isopropanol solution for easier handling.

[0148] The membrane thus obtained had a density of 17.5 g / m 2 It is composed of nanocellulose.

[0149] These films have an inner layer of graphene oxide with a thickness of about 100 nm and outer layers of cellulose with a thickness of about 10 μm each.

[0150] Membrane power of a single layer membrane Tests were carried out using a device made of two independent reservoirs, each containing a sodium chloride (NaCl) solution dissolved at 1 M in the concentrated solution, then 0.1 M, 0.01 M and 0.001 M in the diluent, making it possible to set Rc gradients of 10, 100 and 1000 between the two reservoirs.

[0151] The two reservoirs are separated by a composite membrane according to the invention, obtained as detailed in Example 1.

[0152] Silver grid Ag / AgCl electrodes are immersed in each of the reservoirs on either side of the membrane to measure the current generated across the membrane.

[0153] The results are presented in Table 1.

[0154] [Table 1]

[0155] - U Osmo is the membrane-bound potential from which the Nernst potential of the electrode is estimated (U Nernst) - I Osmo is the membrane-bound current and is calculated by measuring the membrane's electrical resistance according to Ohm's law I=U / R. - P Osmo Max is calculated using the formula Pmax=(UxI) / 4. Membrane power is 1cm 2 Multiplying the value obtained above by 10,000 gives W / m 2 It is expressed as:

[0156] Example 2 Preparation of composite membranes and measurement of membrane power of composite membranes Equipment and raw materials The materials used are the same as those detailed in Example 1.

[0157] The ingredients used in this example are listed below: - cellulose nanofibers negatively charged by carboxymethylation or TEMPO oxidation; - Citric acid, 99% by volume; - Graphene oxide sold by the company Sigma Aldrich under the reference n°777676.

[0158] Preparation of composite membranes The preparation method introduced in this example is detailed below: · 1.75 ml of nanocellulose solution is filtered on a Buchner filter with a PVD filter. The vacuum pump is set to a vacuum of 1 bar; · Once all the solution has been filtered, re-filter 5 ml of citric acid solution on top (acts as a cross-linking agent between the nanofibers); Once the citric acid is filtered, filter 7ml of graphene oxide solution; Once the graphene oxide solution is filtered, re-filter 1.75 ml of nanocellulose solution; · Once all the solution has been filtered, re-filter 5 ml of citric acid solution on top (acts as a cross-linking agent between the nanofibers); Once all the filtered citric acid solution has been pumped, open the Büchner device and remove the filter paper with the filtrate.

[0159] The filter paper / filtrate combination is then placed in a laboratory oven at 85° C. for 15 minutes (drying and cross-linking reaction).

[0160] Finally, the membrane is separated from its filtration medium, possibly having been soaked beforehand in an isopropanol solution for easier handling.

[0161] The membrane thus obtained had a density of 17.5 g / m 2 of nanocellulose and 0.34 g / m 2 It is composed of graphene oxide (2 mass%).

[0162] The nanocellulose content and the mass content of graphene oxide were varied. 2 With a nanocellulose content below this, it is not possible to obtain a film with sufficient mechanical strength.

[0163] For reasons of mechanical strength and ionic resistance, these 17 g / m 2 Values ​​of cellulose and 4 wt.% graphene oxide appear to be optimal.

[0164] Membrane power of composite membrane Tests were carried out using a device made of two independent reservoirs, each containing a sodium chloride (NaCl) solution dissolved at 1 M in the concentrated solution, then 0.1 M, 0.01 M and 0.001 M in the diluent, making it possible to set Rc gradients of 10, 100 and 1000 between the two reservoirs.

[0165] The two reservoirs are separated by a composite membrane according to the invention, obtained as detailed in Example 1.

[0166] Silver grid Ag / AgCl electrodes are immersed in each of the reservoirs on either side of the membrane to measure the current generated across the membrane.

[0167] The results of these measurements are shown in Table 2.

[0168] [Table 2]

[0169] - U Osmo is the membrane potential, from which the Nernst potential of the electrode is estimated (U Nernst) - I Osmo is the membrane-bound current and is calculated by measuring the membrane's electrical resistance according to Ohm's law I=U / R. - P Osmo Max is calculated using the formula Pmax=(UxI) / 4. The membrane power is 2 Multiplying the value obtained above by 10,000 gives W / m 2 It is expressed as:

[0170] It has also been observed that applying a pressure of 3-4 bar to the membrane between two metal plates while heating at 85°C improves the mechanical stability of the membrane by 10-20%. [Explanation of symbols]

[0171] (20A) First reservoir A (20B) Second reservoir B (30A) Electrode (30B) Electrode (22A) Concentration of solute C A An electrolyte solution having (22B) Concentration C of the same solute B An electrolyte solution having (10) A membrane separating the two reservoirs (32) A device that allows the supply of electrical energy generated by the potential difference that exists between two electrodes. (101) Monolayers formed of cellulosic materials containing a network of cross-linked cellulose nanofibers and / or microfibers. (102) An inner layer formed of a second material containing nanoparticles functionalized with charged groups and / or groups that become charged in the presence of water. (103) A second outer layer on the inner layer (102) comprising nanofibers and / or microfibers.

Claims

1. 1. A device for generating electrical energy, comprising: a) a first reservoir A (20A) intended to receive an electrolyte solution (22A) having a solute concentration CA and comprising an electrode (30A) in contact with the electrolyte solution having a concentration CA; b) a second reservoir B (20B) intended to receive an electrolyte solution (22B) having a concentration CB of the same solute, CB being lower than CA, and including an electrode (30B) in contact with the electrolyte solution having a concentration CB; c) a membrane (10) separating two reservoirs, the membrane comprising pores that allow electrolyte to diffuse through the pores from reservoir A to reservoir B; and d) A device (32) that allows the supply of electrical energy generated by a potential difference existing between two electrodes. wherein the membrane comprises at least one layer formed of a cellulosic material comprising a network of crosslinked cellulose nanofibers and / or microfibers.

2. 10. The device of claim 1, wherein the membrane has a thickness between 2 μm and 100 μm.

3. 3. The device according to claim 1 or 2, wherein the thickness of the membrane is between 2 μm and 75 μm.

4. 3. The device of claim 1 or 2, wherein the membrane comprises 10 to 20 g of cellulosic material per m2 of membrane.

5. 5. The device of claim 4, wherein the membrane comprises 15 to 20 g of cellulosic material per square meter of membrane.

6. 3. The device of claim 1 or 2, wherein the crosslinked cellulose nanofibers and / or microfibers are functionalized with negatively charged groups and / or groups that become negatively charged in the presence of water.

7. 7. The device of claim 6, wherein the crosslinked cellulose nanofibers and / or microfibers are functionalized with a group selected from the group consisting of a sulfonate group -SO3-, a carboxylate group -CO2-, an aminodiacetate group -N(CH2CO2-)2, a phosphonate group PO23-; an amidoxine group -C(=NH2)(NOH), an aminophosphonate group -CH2-NH-CH2-PO32-, a thiol group -SH, and mixtures thereof.

8. 3. The device of claim 1 or 2, wherein the crosslinked cellulose nanofibers and / or microfibers are functionalized with positively charged groups and / or groups that become positively charged in the presence of water.

9. 9. The device of claim 8, wherein the crosslinked cellulose nanofibers and / or microfibers are functionalized with groups selected from quaternary ammonium groups -N(R)3+ (where R is C1-C4 alkyl), tertiary ammonium groups -N(H)(R)2+ (where R is C1-C4 alkyl), dimethylhydroxyethylammonium groups -N(C2H4OH)(CH3)2+, and mixtures thereof.

10. 10. The device of claim 9, wherein R is C1 alkyl.

11. 3. The device according to claim 1 or 2, wherein the membrane comprises a monolayer (101) formed of a cellulosic material comprising a network of cross-linked cellulose nanofibers and / or microfibers.

12. 3. The device according to claim 1 or 2, wherein the membrane is a composite membrane comprising two outer layers (101, 103), each formed of a cellulosic material comprising a network of crosslinked cellulose nanofibers and / or microfibers, and between the outer layers is arranged an inner layer (102) formed of a second material comprising nanoparticles functionalized with charged groups and / or groups that become charged in the presence of water.

13. 13. The device of claim 12, wherein the thickness of each of the outer layers (101, 103) is between 2 μm and 25 μm, and the thickness of the inner layer (102) is between 10 nm and 2 μm.

14. The device of claim 12 , wherein the nanoparticles are lamellar nanoparticles.

15. 15. The device of claim 14, wherein the lamellar nanoparticles are metal oxide lamellar nanoparticles, transition metal dichalcogenide lamellar nanoparticles, carbon lamellar nanoparticles, or a mixture thereof.

16. 15. The device of claim 14, wherein the lamellar nanoparticles are lamellar nanoparticles of graphene oxide functionalized on the surface with negatively charged groups or groups that become negatively charged in the presence of water.

17. 16. The device of claim 15, wherein the lamellar nanoparticles of transition metal dichalcogenide are lamellar nanoparticles of molybdenum disulfide.

18. 3. A method for generating electrical energy using a device according to claim 1 or 2, comprising the steps of: i) supplying an electrolyte solution (22A) having a solute concentration CA into a reservoir A (20A) so that an electrode (30A) provided in the reservoir A comes into contact with the electrolyte solution (22A); ii) supplying an electrolyte solution (22B) having the same solute concentration C B into reservoir B (20B) so that an electrode (30B) provided in reservoir B contacts the electrolyte solution (22B), where C B is lower than C A; iii) allowing the electrolyte to diffuse from reservoir A to reservoir B through membrane (10); iv) using the device (32) to capture the electrical energy generated by the potential difference existing between the two electrodes; A method comprising:

19. 19. The method of claim 18, wherein the electrolyte is an aqueous solution containing a solute selected from alkali halides or alkaline earth halides.

20. 20. The method of claim 19, wherein the solute is selected from NaCl, KCl, CaCl2, and MgCl2.

21. 19. The method of claim 18, wherein the concentration ratio CA / CB is greater than 1 and less than or equal to 109.

22. 22. The method of claim 21, wherein the concentration ratio CA / CB is greater than 1 and less than or equal to 105.

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