Electrochemical cell for metal oxidation, system and corresponding process

Abstract

The disclosure relates to an electrochemical cell (ECC) for metal oxidation comprising a chamber (E0) within which are positioned a first electrode (A1) and a second electrode (C2), said cell further comprising means for heating (MC3) the internal volume of said chamber, the cell being configured to receive an electrolyte in a solid form, characterized in that the first electrode (A1) and / or the second electrode (C2) is at least partially covered with at least one anionic transport layer (ATC).

Description

Title of the invention: Electrochemical cell for metal oxidation, system and corresponding method. Field of the invention

[0001] The invention relates to the production of metals. The invention relates more particularly to the production of metals by an electrochemical method. The invention relates more particularly to the electrolysis of metals under conditions unfavorable to the use of liquid electrolyte. Previous Art

[0002] Metallurgy releases a considerable amount of CO2, with iron production alone accounting for approximately 7% of global emissions. Current industrial processes rely on the carbothermic process, which uses graphite for the reduction of metal oxides at high temperatures, according to the following formula:

[0003] 2FeO3 + 3C^ 4Fe+3CO2

[0004] However, this technology is not compatible with carbon neutrality ambitions.

[0005] The alternative relies on high-temperature electrolysis technologies. Three types of metal oxide electrolyzers are currently being explored: the Fray-Farthing-Chen (FFC) Cambridge process, which involves the indirect reduction of a solid (700°C–900°C); the Hall-Heroult® process, which involves the direct reduction of a eutectic (1000°C); and Metal Oxide Electrolysis (MOE), which involves the direct reduction of the metal oxide in its liquid form (1400°C–1600°C). Several companies have positioned themselves in this field, including Boston Metal® with MOE technology and Metalysis® with FFC technology.

[0006] For example, Boston Metal®'s "Molten Oxide Electrolysis" (MOE) technology for steel production is an electrolysis process that eliminates the need for coal in steel production. The developed MOE process and platform can use renewable electricity to convert iron ore into liquid metal. This direct approach eliminates several steps in the steelmaking process, thus avoiding coke production, iron ore sintering and granulation, blast furnace reduction, or refining in an oxygen basic converter. In the MOE platform, an inert anode is immersed in an electrolyte containing iron ore and then electrified. When the cell reaches a temperature of 1600°C, the electrons reduce the iron oxide in the ore, producing pure liquid metal at the cathode. There is no carbon dioxide or other by- Harmful products: the only by-product produced is the oxygen released at the anode. The overall reaction is as follows:

[0007] 4Fe + 3O2

[0008] Furthermore, the MOE platform and cell do not require process water, hazardous chemicals, or precious metal-based catalysts. The result is a clean, high-purity liquid metal that can be sent directly to ladle metallurgy—no reheating is necessary.

[0009] Other actors have also positioned themselves for the in-situ use of regolith for space exploration, in particular for the production of oxygen and metals for the construction of equipment on the lunar surface.

[0010] However, electrolysis technologies for the reduction of oxides suffer from relatively low conversion yields, particularly due to the presence of ionic loops where species reduced at the cathode (e.g., Fe2+) are re-oxidized at the anode (e.g., Fe3+) due to significant diffusion in a liquid electrolyte, and operate at high temperatures (1600°C), which results in a reduction of the range of compatible materials for the design of the electrolysis cell.

[0011] Furthermore, gas / liquid interfaces are problematic in an electrolysis cell in the absence of or under low gravity. Indeed, the separation of gas bubbles from the electrodes is reduced, which induces an accumulation of gas that blocks electrochemical reactions in the absence of gravity.

[0012] It is therefore desirable to have solutions that improve the conversion efficiency during the electrolysis of metal oxides, lower the temperature for the implementation of the electrolysis cell and are better suited to implementation conditions under low gravity by the suppression of a liquid phase.

[0013] The invention improves the situation. Summary of the invention

[0014] The invention improves the situation. More particularly, the invention allows for the implementation of a metal reduction at relatively low temperatures, without necessarily requiring a liquid electrolyte, which makes it possible to produce metal even in the absence of gravity or in the presence of low gravity. More particularly, the disclosure relates to an electrochemical cell for the reduction of metal oxides comprising a chamber in which a first electrode and a second electrode are positioned, said cell further comprising means for heating the internal volume of said chamber, the cell being configured to receive an electrolyte in a (singular) solid form. According to the invention, at least one ion transport layer is located between the first electrode and / or the second electrode and the (singular) solid electrolyte.

[0015] According to a particular feature, the anion transport layer (ATL) is shaped to transport anions from the solid electrolyte to a first electrode while preventing this electrode from being blocked by the production of the gaseous phase at its surface. For example, the anion transport layer is shaped to transport anions to the anode while preventing the oxidation reaction from being blocked by the gaseous phase produced at the anode.

[0016] According to a particular feature, the heating means for the internal volume of said enclosure are configured to deliver a temperature between 500°C and 1200°C.

[0017] According to a particular characteristic, the electrolyte in solid form is a glass.

[0018] According to a particular characteristic, glass belongs to the group comprising: soda-lime glass; borosilicate glass, fused silica, and regolith glass. More generally, it refers to any other amorphous material characterized by a glass transition point (Tg) and a melting point (Tm), such that Tg is lower than Tm, offering within this interval a working temperature range for redox reactions.

[0019] According to a particular characteristic, said at least one anionic transport layer belongs to the group comprising: - molten salts, such as calcium chloride (CaCl2); - eutectics (of molten salts), such as carbonates of lithium and potassium (Li2CO3-K2CO3), so as to lower the melting point; - metals from column 11 of the periodic table of elements such as silver (Ag) or gold (Au); - solid anion-conducting membranes, for example yttrium oxide-stabilized zirconia (YSZ).

[0020] According to a particular characteristic, the first electrode is an anode and the second electrode is a cathode.

[0021] In another aspect, the invention also relates to a process for the electrolysis of an electrolyte in solid form. This process comprises the implementation of an electrochemical cell as described above, into which the electrolyte in solid form is inserted.

[0022] According to a particular feature, the process more particularly comprises: - A step of inserting the electrolyte in solid form into the electrochemical cell; - A step of adding the anionic transport layer to the interface between the first electrode and the electrolyte in solid form; - A step of hermetically sealing the electrochemical cell; - A heating step, using heating means M3, to reach a temperature between the glass transition temperature and the melting temperature of the electrolyte in solid form; - A step of applying a current setpoint across the electrode terminals with a current generator, the current density being selected to initiate the redox process.

[0023] Thus, the electrochemical cell of the disclosure can be used to produce, for example from lunar regolith, metals and oxygen, using energy produced in situ (for example, from solar energy). Since regolith is composed of 99% oxygen, sodium, magnesium, aluminum, silicon, titanium, and iron, it is well suited to the implementation of the electrochemical cell that is the subject of the disclosure. Other implementations of the electrochemical cell can obviously be carried out as needed.

[0024] In another aspect, the invention also relates to conducting electrolysis using a cell as described above. Such conduction comprises the implementation of a computer program executable by a processor, on an electronic control board connected to the various means implemented for the use of the cell described above. Such a computer program controls the implementation of the redox reaction of the electrolyte in solid form, in particular by controlling the temperature within the cell enclosure, by controlling the application of current commands to the electrode terminals, by activating the means for extracting the gases produced during the redox reaction, and by signaling the end of the reaction when certain measured values ​​indicate it. Brief description of the figures

[0025] Other features and advantages of the disclosure will become more apparent upon reading the following description of a particular embodiment, given by way of simple illustrative and non-limiting example, and the accompanying drawings, among which: - [Fig.l] schematically illustrates an electrochemical cell which is the subject of the invention; - [Fig.2a] and [Fig.2b] illustrate the implementation of a first configuration of the electrochemical cell; - [Fig.3a] and [Fig.3b] illustrate the implementation of a second configuration of the electrochemical cell; - [Fig.4a] and [Fig.4b] illustrate the implementation of a third configuration of the electrochemical cell; - [Fig.5] illustrates the current as a function of the voltage applied across the electrode terminals with vitrified regolith in a test of a cell configuration of the invention; - [Fig.6a] and [Fig.6b] illustrate the use of a configuration of the cell of the invention with on the one hand a liquid anionic transport layer and on the other hand a solid anionic transport layer.

[0026] Description of an embodiment

[0027] As indicated above, current electrolytic reduction techniques do not have good conversion efficiency and / or operate over high temperature ranges (>1200°C) and / or use components that are extremely hazardous to human health, such as fluorinated compounds in Hall-Heroult cells, and / or are not suitable for low-severity situations. In this context, the disclosed technique relates to the use of a technique that allows operation at acceptable temperature levels (between 500°C and 1200°C) and at current conversion efficiency levels close to 90% (Faraday efficiency). This technique can also be implemented with many oxides or anionic transport layers, and the results obtained are illustrated herein.

[0028] According to the disclosure, a cross-sectional view of a metal oxidation electrochemical cell (CEL) is described in relation to [Fig. 1]. The CEL comprises a chamber E0 within which a first Al electrode and a second C2 electrode are positioned. The electrochemical cell further comprises heating means MC3 for the internal volume of said chamber. The electrochemical cell is configured to receive an electrolyte E4 in a solid form, for example. According to the disclosure, the first Al electrode and / or the second C2 electrode is at least partially coated with an anionic transport layer (CTA).

[0029] The contact between the solid electrolyte E4 introduced into the electrochemical cell enclosure and the first electrode Al is indirect. It is made via the anion transport layer CTA. The function of the CTA is to transport anions towards the anode without blocking the gaseous phase produced at the anode interface, as detailed below.

[0030] According to the disclosure, the electrolyte in solid form E4 introduced into the enclosure is a glass. For the purposes of this implementation, a glass is an amorphous material characterized by the absence of a crystal lattice. This type of glass could, for example, be soda-lime glass (SLG), which mainly comprises silicon dioxide (SiO2), sodium hydroxide (Na2CO3), and lime (CaO). It could also be borosilicate glass, which is a type of glass that contains silicon dioxide (SiO2) and boron oxide (B2O3) in its chemical composition. It can also be "Fused Silica," also known as fused silica or fused quartz glass, obtained from silicon dioxide (SiO2). In a space application, it can also be "Regolith Glass," a type of glass formed naturally from the melting of regolith, for example, on the lunar surface.

[0031] Furthermore, the implementation of the electrochemical cell may also be of interest for nano- or microcrystalline materials or crystals. However, glasses exhibit distinct transition temperatures (Tm and Tg) that are not necessarily found in crystals. As explained below, the temperature of the electrochemical cell (ECC) should therefore be precisely controlled for these materials.

[0032] Thus, the CEL electrochemical cell for metal reduction comprises, in at least one embodiment, the following elements: - The E0 refractory enclosure, made of high-temperature resistant material, such as alumina or zirconia, to contain the cell and thermally insulate the system. - The Al anode, made of graphite or refractory metal, is where the oxidation of anions takes place. Graphite is a material that is generally consumed and releases CO2 when the anion is oxygen, while refractory metals are ideally used for inert anodes that are not consumed and have a relatively low wear rate. - The cathode C2, made of metal or conductive alloy, where the reduction of metal ions takes place. - The M3 heating system (which can be external), such as a resistive or induction oven, to maintain the cell at the required operating temperature (for example between 500 and 1200°C). - At least one anionic transport layer (ATC), as explained previously. - A solid electrolyte E4, in the form of a glass. - An ISL conduction layer (for example tin) located between the cathode and the solid electrolyte E4, this layer is optional. - Current collectors C5, for example in stainless steel connected to the Al and C2 electrodes to collect electrons and allow the flow of electric current. - J6 seals made of refractory material, such as mica or zirconia, to ensure the cell is sealed and prevent gas leaks, including oxygen produced by the reaction. - An S7 gas extraction system to extract the gases produced (e.g. O2) in the cell.

[0033] This structure makes it possible to create a controlled environment for the electrochemical reduction of vitrified metal oxides while maximizing anodic action by transporting anions out of the solid electrolyte. The dimensions of this cell are adapted to the needs and configurations. The internal volume for receiving the solid electrolyte E4 can range from a few cubic decimeters to several tens of cubic decimeters.

[0034] The proposed technique thus makes it possible to carry out the electrolysis of the material (glass) over a temperature range T such that Tg < T <Tm avec Tg la température de transition du verre et Tm la température de fusion du verre.

[0035] It is worth recalling that the glass transition temperature, also known as the glass transition temperature (Tg), is the temperature at which a glassy material changes from a rigid solid state to a rubbery and elastic state. This transition occurs when the molecular chains of the glass begin to move and reorganize in response to increasing temperature. Below the glass transition temperature, the glass is in a rigid solid state, with a disordered and amorphous molecular structure. Above the glass transition temperature, the glass becomes softer and more elastic, with a more fluid and mobile molecular structure. The glass transition temperature is generally between 500°C and 1200°C for common glasses and varies depending on the composition and molecular structure of the glass.The melting point of glass (Tm) is the temperature at which a vitreous material changes from a solid to a liquid state. This temperature depends on the chemical composition and molecular structure of the glass, as well as the heating rate during the melting process. When glass is heated to its melting point, the molecular chains begin to break down and rearrange, resulting in a loss of viscosity and increased fluidity. The following table illustrates the temperature ranges for the glasses described above: Tg (°C) Tm (°C) Soda-Lime Glas s 500 1000 Boro-Silicate Glas s 700 1200 Fused Silica 1200 2200 Regolith Glas s 600 1200

[0036] In these temperature ranges, depending on the glass used, ionic conductivity is activated and electrochemical reactions are possible with the reduction of cations (Cm+) at the cathode and the oxidation of anions (An) at the anode.

[0037] It should be noted that ionic conductivity differs from electrical conductivity: although the two quantities are often expressed with the same symbols (δ - sigma) and units (S / cm), these two conductivities are different. Ionic conductivity is generated by the movement of ions under the influence of an electric field. The movement of ions takes place in an electrolyte such as solids and solutions. Ionic conductivity is measured with signals on the order of kHz. In contrast, electrical conductivity is generated by the movement of charge carriers such as electrons or holes in a metal or semiconductor. Electrical conductivity can be measured with direct current or alternating current signals. Both conductivities can sometimes be found in the same medium, particularly at temperatures above 1000°C.However, at room temperature, ionic conduction can be considered the only type of conduction through an electrolyte.

[0038] As previously stated, the architecture of the electrochemical cell is adapted to allow the evacuation of the gaseous phase generated at the anode. Indeed, the viscosity of the glass over this temperature range does not allow the gas bubbles to be released from the electrode (anode)-glass interface.

[0039] The electrochemical cell thus described can operate over relatively high current ranges (~0.1–2 A / cm²) for the reduction of vitrified metal oxides in a relatively low temperature range (500–1200°C). The solid electrolyte E4 can resemble a singularly cylindrical bar whose diameter and length are not limited. The electrodes (Al and C2) are positioned at each end of the cylindrical bar. The CTA, described below, is positioned between the anode and the cylindrical bar. The potential applied between the electrodes is singularly proportional to the equivalent resistance induced by the cylindrical bar. The ionic conductivity of the glass is estimated to be between 0.1 and 1 S / cm over the considered temperature range. The Joule effect generated through the cylindrical bar helps maintain the cell at temperature.

[0040] Furthermore, some glasses contain volatile elements in their reduced metallic form at the cathode, for example, metallic sodium, which evaporates at a temperature of 883°C, and magnesium, which evaporates at a temperature of 1090°C. For this reason, the inventors determined that it is advantageous to work at relatively low temperatures T, between Tg < Ts < Tg, where Ts is the vaporization temperature of the most volatile elements.

[0041] More particularly, considering that for T between Tg < T < Tm the ionic conductivity is activated, the constituent elements of the glass can be reduced, in particular the cations, at the cathode according to the reaction:

[0042] Cm* + me - C° (D

[0043] with C°, the metallic phase of the Cm+ cation and, the anions can be oxidized at the anode according to the reaction:

[0044] A0 + ne(2)

[0045] However, the A° form is generally a gaseous form which cannot be properly evacuated from the glass / anode interface over the temperature range considered.

[0046] To improve this interface, an anion transport layer (ATL) is introduced according to the invention. The ATL's function is to transport anions to the anode without blocking the generation and evacuation of the gaseous phase produced at the interface between the metal oxide and the anode. The ATL can be a molten salt (NaCl, CaCl2, etc.), a low-viscosity eutectic (e.g., a mixture of salts), a liquid metal (e.g., silver, gold), or a solid such as yttrium-stabilized zirconia (YSZ). The ATL is selected according to the operating range defined by the glass temperatures Tg and Tm.

[0047] For example, a eutectic such as CaCl2-NaCl is a good CTA when Tg < 900°C. The liquid eutectic layer between the solid electrolyte E4 and the Al anode is between 0.1 cm and 5 cm thick. Liquid silver is more suitable for temperatures 1000°C < Tg < 2000°C, such as for fused silica, as liquid silver has a higher boiling point than salts. Similarly, the liquid metal layer acting as the CTA is between 0.1 cm and 5 cm thick.

[0048] When a metallic CTA is desired, it is selected from column 11 of the periodic table of elements, with an intermediate melting point (900-1100°C) and a high oxidation potential (difficult to oxidize).

[0049] When a liquid phase is not desired, the ATC can be a solid anion-conducting membrane onto which an electrode is sintered. Such a membrane allows only anions to flow and conducts them to the anode. For example, technologies developed for solid oxide fuel cells (SOFCs) can be adopted, using half-cells of the YSZ / LSM (Lanthanum strontium manganite) or YSZ / Ni type, or others, to remove the oxygen produced at the interface with the glass in cases where the anion in the glass is oxygen (O2). The YSZ membrane operates over temperature ranges of 500 to 1100°C, and the membrane thickness ranges from 1 µm to 5 mm.

[0050] Also, if the properties of the glass allow it, a specific, particularly porous anode, allowing the evacuation of gases produced by the oxidation reaction can The anode can be prepared directly on the glass surface. For example, a porous anode specifically designed for the electrolysis of glasses below their melting point can be used. The porous anode is configured to oxidize anions and vent gases from the reactive interface. This option reduces the need for a CTA (Controlled Air Transfer).

[0051] The CTA can also, in certain situations, be the glass itself in which a temperature gradient is applied such that the temperature T < Tm at the cathode but T > Tm at the anode.

[0052] With the introduction of the CTA and the electrolysis of the glass for Tg < Tm, the faradaic efficiency, which is the level of electrochemical conversion of the electrons injected into the system, is estimated to be close to 90%. Indeed, the inventors have determined that under these conditions, the evolution of gases at the cathode is suppressed, as are the electrical conductivity through the electrolyte and the ionic loops within the electrolyte.

[0053] Thus, the described technique makes it possible to exploit the properties of glasses over this temperature range for the production of metals, in particular under variable gravitational conditions (in the absence of gravity or with low gravity, where conventional liquid electrolytes cannot be used), as well as in the nuclear industry.

[0054] Figures 2a to 4b illustrate several embodiments of the electrochemical cell of the invention, in which several anionic transport layers and several electrochemical cell configurations are shown (the electrochemical cell configurations are shown in cross-sectional view). The heating means are not shown in these figures.

[0055] Figure 2a illustrates a cross-sectional view of a first example of the configuration of the electrochemical cell CEL in a three-electrode setup. In this first example, the electrochemical cell CEL comprises a graphite anode Al in a vertical position, penetrating the upper part of the CEL cell. The CEL cell also comprises a graphite cathode C2, forming a horizontal base of the CEL cell. Finally, a reference electrode e-ref55 is introduced beforehand into the soda-lime glass SLG by heating it above its melting point (Tm). The reference electrode is a nickel-chromium wire. A temperature probe Stemp is also introduced. The electrochemical reaction volume is delimited by a cylindrical enclosure E0 made of alumina, which acts as an insulator.In this example implementation, the electrochemical cell is biased with 2 Volts between the cathode and the anode while a reading of the reference electrode potential is taken.

[0056] The reaction volume of the CEL cell comprises a layer of tin in the liquid state (when heated), in contact with the graphite cathode C2, the soda-lime glass SLG, whose reduction we wish to carry out, and calcium chloride CaCl2 (eutectic) in contact with the anode Al which acts as the CTA. As illustrated in [Fig. 2b], the potential of the reference electrode stabilizes around T0 = 250°C during heating. For T < T0, the reference electrode is floating. An S → L transition is visible and corresponds to the solid-liquid transition of CaCl2 at 772°C. In the configuration described in [Fig. 2a] and whose result is presented in [Fig. 2b], it is considered that soda-lime glass (SLG) behaves as a material with no viscosity, i.e., with an infinite coefficient, below the melting point Tm (~1000°C), but whose ionic conductivity is activated from 250°C when the potential of the reference electrode is stabilized, as illustrated in [Fig. 2b].

[0057] Figure 3a illustrates a second example of the configuration of the electrochemical cell CEL in which two electrodes are used. The electrochemical cell CEL thus comprises an anode Al, in a vertical position, penetrating the upper part of the cell. The cell CEL also comprises a cathode C2, forming a horizontal base of the cell. The electrochemical reaction volume is delimited by a cylindrical enclosure E0 made of alumina, which acts as an insulator. In this embodiment, the electrochemical cell CEL also includes the temperature measurement device D3.The reaction volume of the CEL cell comprises soda-lime glass (SLG) with a base approximately 2 cm thick and 3 cm in diameter, which is to be reduced at cathode C2, and a mixture of lithium and potassium carbonates, Li2CO3-K2CO3 (eutectic), acting as the CTA in contact with the anode Al and soda-lime glass (SLG) E4. Figure 3b shows the temperature, current density, and voltage measurements between the cathode and anode over a 50-minute period. It can be observed that the cell voltage tends to decrease at constant current density and stabilizes between 20 and 30 V. The maximum current density during this configuration is approximately 0.4 A / cm².

[0058] Figure 4a illustrates a third example of cell configuration In this electrochemical setup, glass (E4) is directly integrated onto the cathode in the form of a solid cylinder 2 cm in diameter and 3 cm high. The anode (Al) is a cylinder approximately 5 cm in diameter and 2 cm high, the internal volume of which is at least partially filled with a mixture of lithium and potassium carbonates, Li2CO3-K2CO3 (eutectic), which acts as the CTA. Figure 4b shows the values ​​of the temperature, the potential between the anode and the cathode, and the current density over a 30-minute period. The current density gradually increases while the voltage stabilizes between 20 and 30 V. Oscillations in the potential are observable and are due to the accumulation of gases. the glass cylinder which is produced on the anode. A maximum current density of approximately 1 A / cm2 is reached during the test.

[0059] During the two tests shown in [Fig. 3a], 3b, 4a, and 4b, the cell temperature did not exceed 780°C, which is below the vaporization temperature of metallic sodium and the melting point of glass. A metallic deposit was visually observed between the cathode and the glass, the composition of which is a ternary mixture of the metal oxides composing the glass, namely sodium, calcium, and silicon in their metallic form. The experiments thus proved that it is possible to reduce metal oxides to a vitrified form below the melting point (Tm) with the addition of an anionic transport layer (CTA).

[0060] Finally, [Fig. 5] shows the current as a function of the voltage applied across the electrodes with vitrified regolith, the shape of which is a round bar 1 cm in diameter and 2 cm high resting on a graphite cathode. Two tests of the cell were carried out with the regolith: for the first of these tests, the CTA took the form of a layer of CaCl2 and for the second, liquid silver. The tests of these configurations were carried out between 800 and 950°C. In both cases, it is possible to measure a relatively stable current through the round regolith bar at a temperature below the melting point (Tm) of the regolith, which validates the technique used and the purpose of the disclosure.

[0061] These various embodiments demonstrate that the temperature To at which ionic conduction begins is lower than the melting temperature Tm of the glass. This can be used to reduce glass to a lower temperature than traditional methods without emitting carbon dioxide. This technique can be implemented on a wide variety of available glass (TiO2, Fe2O3, amorphous regolith, etc.). This is made possible by the anionic transport layer (ATL). This technology is not directly or indirectly dependent on gravity when the ATL is solid and can be used to produce deoxygenated materials for space programs.

[0062] A simple method for producing such materials is as follows, as shown in Figure 6.a. with a liquid CTA and Figure 6.b. with a solid CTA: - The cell is prepared, according to the designs, to accommodate the selected glass; - The selected glass is inserted into the cell; - Then a CTA is added to the interface between the Al anode and the glass; - The cell is then hermetically sealed and the M3 heating means are put into operation, until a temperature between Tg and Tm allows the redox processes to begin; A current signal is applied across the electrodes using a current generator. The current density is selected to initiate the redox processes without damaging the thermistor or the anode. The current generator adjusts to apply the appropriate voltage to achieve the desired current density. Once the system is stable, electrolysis at a specific current can be performed. The duration depends on the quantity of material to be reduced. For example, a volume of 1 cm³ of soda-lime glass (SLG) is completely reduced in 9 hours of electrolysis at a density of 0.5 A / cm² and a potential of 2 to 50 V, generating approximately 1 liter of pure oxygen under standard conditions. The glass reduction occurs at the cathode, while the gases produced by the oxidation reaction are generated at the anode. - Once the amount of material to be reduced has been reached, the system is stopped and the result of the process is collected and cooled outside the cell. The ATC is recycled.

[0063] Process variations can be considered, for example, a continuous extraction process for the materials in their reduced form. In this case, a high-temperature zone is necessary to melt the metal oxides above their melting point Tm. The cathode reaction takes place below the melting point Tm and the glass transition temperature Tg. The anode reaction can be carried out above or below the melting point Tm, using respectively an inert anode for high temperatures or a CTA combined with a low-temperature inert anode.

[0064] Also, if the properties of the anode allow it, the anode can be directly prepared on the solid electrolyte (E4) with, for example, the sintering of porous materials allowing the evacuation of the gaseous phase generated between the solid electrolyte and the anode.

[0065] Finally, in the case of a system operating under vacuum, the oxidation reaction can be further driven by the thermionic effect. The thermionic effect is the emission of electrons into the vacuum from the surface of materials with increasing temperature. The emission of electrons J is described by the Richardson equation:

[0066] J=AgT2 exp(-O> / kbT)

[0067] with T the temperature of the metal in Kelvin, O the work function of the metal, kb the Boltzmann constant and AG the Richardson constant.

[0068] The cell that is the subject of this disclosure is of particular interest for the implementation of carbon-free metal production at reasonable temperatures, requiring reduced electrical heating power. Indeed, the configuration proposed in the prototype demonstrates that the electrical power required for the cell's operation is compatible with power sources such as photovoltaic panels or individual wind turbines. Such photovoltaic panels can be installed in uncontrolled environments. The main advantage, therefore, lies in the fact that a system comprising multiple photovoltaic panels or other means of generating green electricity can be connected to one or more cells to generate metals and oxygen, which, if necessary, is stored in a tank adapted for this purpose.This oxygen is then used as a reserve for the production of other elements, or for consumption (for example, in an ambient air recycling system).

[0069] In other situations, the implementation of the solution described herein can be carried out in dedicated industrial facilities. In such cases, the dimensions of the cells are modified, in particular to enable them to produce larger quantities of oxygen and metals. The cells can be connected in series or in parallel. The objective of this implementation is to promote the use of non-carbon-based electricity to facilitate metal reduction.

[0070] In the context of an implementation on the lunar surface, the cell can also be powered by a locally produced energy source designed for the space environment.

Claims

Demands

1. Electrochemical cell (ECC) for the reduction of metal oxides comprising a chamber (EO) within which are positioned a first electrode (Al) and a second electrode (C2), said cell further comprising means for heating (MC3) the internal volume of said chamber, the cell being configured to receive an electrolyte (E4) in a solid form, characterized in that the first electrode (Al) and / or the second electrode (C2) is at least partially covered with at least one anionic transport layer (ATC).

2. Electrochemical cell (ECC) according to claim 1, characterized in that the anionic transport layer (ATL) is shaped to transport the anions of the electrolyte (E4) in a solid form to the Al electrode or the C2 electrode, while avoiding blocking the reaction of this electrode by the production of the gaseous phase on its surface.

3. Electrochemical cell (ECC) according to claim 1, characterized in that the heating means (MC3) of the internal volume of said enclosure are configured to deliver a temperature between 500°C and 1200°C.

4. Electrochemical cell (ECC) according to claim 1, characterized in that the electrolyte (E4) in solid form is an amorphous material characterized by a glass transition point (Tg) and a melting point (Tm) such that Tg < Tm and an operating temperature of the electrochemical cell between Tg and Tm.

5. Electrochemical cell (ECC) according to claim 1, characterized in that the electrolyte in solid form is a glass.

6. Electrochemical cell (ECC) according to claim 4, characterized in that the glass belongs to the group comprising: soda-lime glass; borosilicate glass; fused silica; regolith glass

7. Electrochemical cell (ECC) according to any one of claims 1 to 5, characterized in that said at least one anionic transport layer (ATL) belongs to the group comprising: - molten salts; - eutectics, in particular molten salt eutectics; - metals from column 11 of the periodic table of elements; - solid anion-conducting membranes.

8. Electrochemical cell (ECC) according to claim 1, characterized in that the first electrode (Al) is an anode and the second electrode (C2) is a cathode.

9. A process for electrolyzing an electrolyte in solid form, the process comprising the implementation of an electrochemical cell (ECC) according to any one of claims 1 to 7, within which the electrolyte in solid form is inserted.

10. The method according to claim 9, characterized in that it comprises: - A step of inserting the electrolyte in solid form into the electrochemical cell (ECC); - A step of adding the anionic transport layer (ATL) to the interface between the first electrode (Al) and the electrolyte in solid form; - A step of hermetically sealing the electrochemical cell (ECC); - A heating step, using heating means M3, to reach a temperature between the glass transition temperature (Tg) and the melting temperature (Tm) of the electrolyte in solid form; - A step of applying a current setpoint across the electrodes with a current generator, the current density being selected to initiate the redox process.

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