Electrochemical cell for the electrolysis of liquid water or water vapor, manufacturing process and uses

Abstract

An electrochemical cell for the electrolysis of liquid water or water vapor includes a proton-conducting electrolyte (3) made of aluminosilicate, sandwiched between a porous metal anode (2) and a porous electronic conducting cathode (4). Preferably, the porous metal anode (2) is a sintered stainless alloy comprising at least 18% chromium. Also, a method of manufacturing such a cell includes at least: manufacturing the proton-conducting aluminosilicate electrolyte (3) and deposition of said electrolyte (3) on the porous metal anode (2) by hydrothermal method, and depositing the electronic conducting porous cathode (4) on the electrolyte (3) to form the electrochemical cell (1). The electrochemical cell can be used for, amongst other compounds, the reduction of oxidized compounds, such as the oxidized compounds constituted, for example, by carbon dioxide.

Claims

1. An electrochemical cell for the electrolysis of liquid water or water vapor, comprising: a porous sintered metal anode, an electron conducting porous cathode, and a proton conducting inorganic electrolyte made of aluminosilicate, sandwiched between the porous metal anode and the electron conducting porous cathode, wherein the electrolyte comprises a first layer consisting of aluminosilicate and a second layer which is a diffusion layer comprising aluminosilicates of metal elements diffused from the porous metal anode into the electrolyte.

2. The electrochemical cell according to claim 1, wherein the porous metal anode is a sintered stainless alloy comprising at least 18% chromium.

3. The electrochemical cell according to claim 2, wherein the sintered stainless alloy comprises nickel and/or cobalt and/or iron.

4. The electrochemical cell according to claim 2, wherein the diffusion layer further comprises complexes of the metal elements diffused from the porous metal anode into the aluminosilicate electrolyte, wherein the complexes of the metal elements result from complexing of the metal elements of the porous metal anode with oxycarbonated compounds.

5. The electrochemical cell according to claim 4, wherein the oxycarbonated compounds are selected from formaldehyde, ethanol, carboxylic acids, and mixtures thereof.

6. The electrochemical cell according to claim 1, wherein the porous electron conducting cathode is based on at least one selected from the group consisting of transition metals and metals selected from the group consisting of Groups IVB, VB, VIB, VIIB, VIIIB, IB, and IIB, and their alloys.

7. The electrochemical cell according to claim 6, wherein the porous electron conducting cathode comprises palladium.

8. The electrochemical cell according to claim 1, wherein the porous electron conducting cathode is made up of carbonaceous compounds.

9. An electrochemical cell according to claim 8, wherein the carbonaceous compounds are at least one selected from graphene, carbon nanotubes, and couplings of carbon compounds with at least one selected from the group consisting of transition metals or metals selected from the groups IVB, VB, VIB, VIIB, VIIIB, IB, and IIB, and their alloys.

10. The electrochemical cell according to claim 1, wherein the aluminosilicates are in the form of silicates selected from the group consisting of dickite from the kaolinite group, clinochlore from the chlorite group, and zeolites.

11. The electrochemical cell according to claim 1, which has a tubular configuration.

12. A method of manufacturing an electrochemical cell, the method comprising: manufacturing an aluminosilicate proton conducting electrolyte and depositing the electrolyte on a porous metal anode by hydrothermal method, and depositing an electron conducting porous cathode on the electrolyte, so as to form the electrochemical cell according to claim 1.

13. The method according to claim 12, wherein the manufacturing of the electrolyte and the depositing of the electrolyte on the anode are carried out in an autoclave under a pressure in a range of from 1 to 100 bars and comprises: mixing powders comprising at least silica and alumina, introducing an aqueous solution into the autoclave, wherein the solution has basic character and a pH in a range of from 8 to 10 as a result of addition of a base, introducing the sintered stainless alloy anode in the autoclave, introducing a noble metal cathode, increasing autoclave temperature, polarizing the anode and the noble metal cathode, so as to result in dissolution of the powders and deposition of these powders on the anode accelerated by the polarization.

14. The process according to claim 13, wherein additives selected from the group consisting of alkali metal salts and alkaline earth compounds are added to the mixture of silica and alumina, as well as oxycarbonated compounds.

15. The process according to claim 13, wherein the increase in temperature of the autoclave is carried out until a temperature in a range of from 300 C. to 400 C. is reached and is then maintained for a time in a range of from 1 to 5000 hours.

16. The method according to claim 13, wherein the solution has basic character and a pH in the range of from 8 and 10 as a result of addition of at least one selected from the group consisting of ammonia, ethanol amine and morpholine.

17. The process according to claim 12, wherein the deposition of the electron conducting porous cathode is carried out on the electrolyte by at least one selected from the group consisting of physical deposition, spraying, spray coating, electroplating, and chemical deposition of at least one selected from the group consisting of: metal compounds selected from the group consisting of transition metals, metals selected from the Groups IVB, VB, VIB, VIIB, VIIIB, IB, and IIB, and their alloys, followed by an electrolytic or chemical deposition of copper, and carbon compounds.

18. The process according to claim 17, wherein the cathode is deposited on the electrolyte by at least one selected from the group consisting of physical deposition, spraying, spray coating, electroplating, and chemical deposition of carbon compounds selected from the group consisting of graphene, carbon nanotubes, and couplings of carbon-containing compounds with at least one metal compound selected from the group consisting of transition metals and alloy metals selected from the groups IVB, VB, VIB, VIIB, VIIIB, IB, and IIB, and their alloys.

19. The process according to claim 18, wherein the cathode is deposited on the electrolyte by coating graphene oxide coating which is subsequently reduced chemically, electrochemically or physically.

20. The process according to claim 12, wherein the deposition of the electrolyte is performed hydrothermally.

21. A method of reducing oxidized compounds, by reactive chemical species formed by the electrolysis of water, comprising: carrying out a reduction in the cathode compartment of the electrochemical cell according to claim 1, at temperatures in a range of from 100 to 400 C., so as to obtain at least one selected from the group consisting of (i) production of hydrogen in the cathode compartment, and (ii) oxidation of reduced compounds in the anode compartment.

Description

(1) Other features and advantages of the invention will become apparent from the description below, which is given as an example and not restricted to, with reference to the appended figures amongst which include:

(2) FIG. 1 is a schematic cross sectional view of the electrochemical cell of the invention,

(3) FIG. 2 is a photograph taken by Scanning Electron Microscope of the aluminosilicate electrolyte after being deposited on the sintered anode, and

(4) FIG. 3 is a cross sectional photograph taken by Scanning Electron Microscope of the aluminosilicate electrolyte deposited on the sintered anode,

(5) FIG. 4 is a photograph taken by Scanning Electron Microscope showing the silica rosette formation of an anode in a silicate medium, and

(6) FIG. 5 is a photograph taken by Scanning Electron Microscope of the nickel electroplating of the cathode on the aluminosilicate electrolyte.

(7) The electrochemical cell of the invention comprises an inorganic electrolyte aluminosilicate which is produced and then deposited by hydrothermal method onto an anode made of sintered metal. The cathode made of a porous electron conductive material is then deposited onto the electrolyte.

(8) With reference to FIG. 1, the electrolyser 1 of the invention includes an anode 2, an aluminosilicate 3 electrolyte, a cathode 4 and a generator 5 which generates a current with a potential difference between the anode 2 and the cathode 4.

(9) The electrolyser 1 also includes means 6 for the introduction of oxidized gaseous compounds under pressure into the cathode compartment 4 and means 7 for introducing pressurized water vapor or liquid into the anode compartment 2.

(10) Water is oxidized at the anode 2, releasing electrons, releasing oxygen and forming H.sup.+ ions which migrate through the electrolyte to the surface 3 of the cathode 4 where they are reduced to H adatomes which react with the gaseous oxidized compounds by forming compounds of hydrocarbons such as methane and ROH alcohols. These H adatomes can also lead to the formation of hydrogen by pairing at the cathode side 4.

(11) As illustrated in FIG. 1, the electrolyser 1 of the invention may have a tubular shape. This tubular configuration is advantageous as a result of the large exchange surfaces it generates with the gaseous oxidized compounds on the cathode side and the pressurized water on the anode side.

(12) With this tubular configuration, provision can be made for an assembly of tubular electrochemical cells either in series or in parallel on a ferrule which is comparable to the geometry of the heat exchangers.

(13) The electrolyser 1 can also be flat or have any other configuration adapted to its application.

(14) The use of aluminosilicate to achieve the electrolyte 3 has numerous advantages.

(15) Firstly the resulting electrolyser 1 operates at temperatures of between 100 and 400 C. These medium temperatures help limit corrosion of the electrodes.

(16) In addition, the aluminosilicates have good properties of adhesion to metal, which results in the possibility of using a non-noble metal anode.

(17) Moreover, and as will be detailed later, the aluminosilicate may be subject to a deposit on the anode, which results in the ability to use any type of geometric configuration for the anode assembly/electrolyte/cathode, that is to say, the heart of the electrolyser, and thus a general adaptation of the geometrical configuration of the electrolyser for the intended application.

(18) More specifically, the aluminosilicate constituting the electrolyte is a phyllosilicate-type aluminosilicate and/or zeolite.

(19) Both structures have the advantage of having a conductivity which changes according to the water content.

(20) More specifically, the phyllosilicates are made of superimposed laminae formed of layers of SiO.sup.4 tetrahedra and octahedra layers Al(OH).sub.6 connected by oxygen atoms and OH-ions which are shared. The presence of Al.sup.3+ ions instead of Si.sup.4+ ions induces a negative charge to the network. The negative charge of each lamina is compensated by the charge of intercalary cations such as Fe.sup.2+, Al.sup.3+, Mg.sup.2+, Mn.sup.2+ or Ni.sup.2+ which are hydroxylated, or even H.sup.+ protons all of which participate in the mobility of protons.

(21) Two particular phyllosilicates are preferentially formed, these are, dickite which belongs to the kaolinite group and clinochlore which belongs to the chlorite group.

(22) Alternatively, the aluminosilicate may be a zeolite which also has a cage structure consisting of Si.sup.4+ ions and Al.sup.3+ ions which are connected by O and OH-atoms that are shared.

(23) The anode 2 consists of a sintered stainless alloy comprising at least 18% chromium as well as iron, nickel and/or cobalt.

(24) The use of such materials to produce the anode is advantageous both in terms of corrosion since these alloys corrode very superficially, but also to ensure good adhesion of the aluminosilicate deposit as is detailed further.

(25) The cathode 4 is made of a porous deposit which can be produced using transition metals or metals selected from the Groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, and their alloys. It is preferable to use transition metal alloys such as nickel and its alloys, cobalt and its alloys or copper alloys. Advantageously, the porous deposit also includes palladium associated with copper which is a good catalyst for carbon dioxide reduction reactions.

(26) Alternatively, the cathode 4 is made of carbon compounds such as carbon nanotubes or graphene, or a coupling of carbon-containing compounds with at least one transition metal or alloy of metals selected from the Groups IVB, VB, VIB, VIIB, VIIIB, IB, IIB, and their alloys.

(27) The following describes a non-restrictive example of the electrolytic production process of the invention.

(28) The manufacture and deposit of aluminosilicate electrolyte on the anode made of sintered metal are performed hydrothermally. Hydrothermally means in an aqueous medium which can be pressurized.

(29) The first step involves the mixing of powders in a de-aerated autoclave. The powder mixture contains at least silica and alumina. Additives for stabilizing the powders and neutralizing the surface of the silica can be added. These additives are selected from alkali metal salts (Na, K, Li, NH.sup.4+) and alkaline earth metals (Mg, Sr, Ca, Ba).

(30) An alkaline aqueous solution of pH between 8 and 10 is introduced into the autoclave. This basic solution is produced by addition of a base such as ammonia, ethanol amine or morpholine. The alkalinity of the solution facilitates the dissolution of the silica and alumina.

(31) Oxy-carbonaceous complexing compounds such as formaldehyde or carboxylic acids are also introduced into the autoclave. The previous bases ethanolamine, morpholine are also complex-forming agents. These elements promote the complexing of the metal elements constituting the metal anode and even superficial dissolution, thus generating the formation of aluminosilicates of these metal elements, which allows for a good adhesion of the aluminosilicates at the anode. We then observe on cell 1 the presence of a diffusion layer of metal elements constituting the metallic porous anode 2 in the aluminosilicate.

(32) The anode consisting of a sintered stainless alloy is also introduced into the autoclave as previously described. The anode may be coated with an iron layer to promote adhesion of the electrolyte and to increase the thickness of the electrolyte deposition by substitution of aluminum in the aluminosilicate.

(33) An Ag/AgCl type reference electrode is placed in the bottom of the autoclave to measure and control the anode voltage.

(34) The atmosphere of the autoclave is then heated to about 300 C. and the pressure adjusted between 1 and 100 bars. The powders dissolve up to 250 C. and then precipitate at around 300 C. During the dissolution, the aluminum is substituted for silicon by creating a negatively charged crystalline network into which the protons are inserted.

(35) It is possible to improve the densification of the aluminosilicates of the metal elements of the anode and accelerate the production and deposition of aluminosilicates onto the anode electrochemically.

(36) In order to do this, a cathode in the form of a platinum grid is also placed in the autoclave. The electrodes are then polarized in the stability region of water at between 600 and +800 mV/hydrogen electrode, with a potential difference of 600 mV between the anode and the cathode.

(37) In this way, the densification of aluminosilicates on the anode increases. A densification of 90% is targeted. The thickness of this densified layer is optimized according to the desired ohmic drop during use of the electrolyser under pressurized water vapor, or liquid water.

(38) It should be noted that if the anode acts as an electrode both during the manufacture of the electrolyser and in use, the cathode placed in the autoclave only acts as an electrode in the case of the deposition of aluminosilicates on the anode.

(39) The time during which the atmosphere of the autoclave is maintained at 300 C. varies between 1 and 5000 hours. When using the electrochemical method which has just been described, the time at temperature of the atmosphere of the autoclave will be greatly reduced. On the contrary, without using electrochemical means, the time at temperature of 300 C. may be several hundreds of hours up to 5000 hours.

(40) Alternatively, the anode can be first immersed in a sol-gel process prior to the deposition of powder by hydrothermal method as previously described.

(41) The photograph of FIG. 2 shows the deposition of the aluminosilicate electrolytes grafted onto the anode. This deposition was obtained by a mixture of silica and alumina to which additives were added in the form of calcium phosphate and calcium carbonate to stabilize the powders, as well as amines, acetates and formates to improve the adhesion of the aluminosilicates on the anode.

(42) The deposition of powders on the anode is performed at rest potential for many hundreds of hours at a temperature of 250 C.

(43) We see in this figure the alveolar aspect of the aluminosilicate electrolyte.

(44) FIG. 3 shows the aluminosilicate electrolyte 3 in section comprising a dense portion 10 with a thickness of about 0.868 nm in contact with the anode 2, and a portion which is alveolar 11 at rest potential.

(45) The acceleration of the rate of deposition can be obtained by galvanostatic polarization and/or potentiostatic anode from room temperature as shown in FIG. 4 with silica rosette formation on an anode in a silicate medium and by applying a potential difference of 2 volts between the anode and cathode.

(46) After the deposition of the electrolyte 3 has been performed on the anode 2, the assembly is removed from the autoclave and deposition of the cathode 4, described above, is performed on the electrolyte 3.

(47) Four types of depositions on the cathode were tested. chemical nickel plating with a Brenner solution (NiCl.sub.2.6H.sub.2O 30 g/l, NH.sub.4Cl 50 g/l and (NH.sub.4).sub.2HC.sub.6H.sub.5O.sub.7 to 65 g/l) followed by an electrolytic deposition of copper or a copper plating with a solution of SnCl.sub.2, CuSO.sub.4, 5H.sub.2O, sodium citrate and formaldehyde at pH 3. an electrolytic nickel deposition in sulphamate medium ((NH.sub.2SO.sub.3).sub.2Ni 300 g/l H.sub.3BO.sub.3 40 g/l at pH 7 and a temperature of 60 C.) in galvanostatic mode between 0.05 and 100 mA/cm.sup.2. This deposition can be followed by an electrolytic deposition of copper in a copper sulphate medium. FIG. 5 thus illustrates the porous nickel deposition obtained by the electroplating on the aluminosilicate layer. The energy-dispersive x-ray spectroscopy (EDX) shown in the same figure, characterizes the presence of nickel from the aluminosilicate layer containing iron from the support. deposition under vacuum using an electron gun deposition of graphene through the graphene oxide coating subsequently reduced by chemical, electrochemical or physical means.

(48) As mentioned above, the electrolyser of the invention is preferably used at operating temperatures between 100 and 400 C. The electrolyser produces hydrogen by hydrogenation, or reduction of the oxidized compounds such as carbon dioxide in the cathode compartment.