FR3161913A1 - Manufacturing process for a porous nano-architectural ceramic for electrolysis cell electrode - Google Patents

Abstract

A process for manufacturing a porous nano-architectural ceramic (200) for an electrolyzer cell electrode (100), in particular for a high-temperature electrolyzer cell electrode (also known as an EHT), the process comprising the following steps: provision of a resin comprising a polymeric photoreagent, a solvent, for example an organic solvent, and a filler including at least one mineral precursor of the ceramic; 3D printing of the resin according to a predetermined pattern to form a porous nano-architectural skeleton (300), for example in the form of a honeycomb or in the form of a tetrakaidecahedral skeleton; and sintering of the porous nano-architectural skeleton (300) to obtain a porous nano-architectural ceramic (200). Figure 4

Description

Manufacturing process for a porous nano-architectural ceramic for electrolysis cell electrode Technical field of the invention

The invention relates to the field of hydrogen production by electrolysis of water vapor.

The invention relates in particular to a method for manufacturing a porous nano-architectural ceramic to constitute an electrode for an electrolyzer cell.

According to a second aspect, the invention also proposes a method for producing an electrolyzer cell.

According to a third aspect, the invention relates to a porous nano-architectural ceramic obtained by implementing the manufacturing process.

State of the art

In the current energy context, where fossil fuel reserves are dwindling, energy consumption is constantly rising, and the need for clean, sustainable, and greenhouse gas-free technologies is becoming increasingly urgent, hydrogen is emerging as an energy carrier capable of directly competing with electricity and heat. However, since hydrogen is rare in nature, it is necessary to implement technological solutions to produce it on a large scale at a competitive cost.

One possibility, among others, relies on high-temperature steam electrolysis (also known as HTE). The process involves splitting the water molecule into hydrogen and oxygen at high temperatures. This requires a heat source, which can be found in nuclear power or renewable energy sources (geothermal or solar). Another technological challenge lies in developing an electrolyzer, and in particular an electrochemical cell, capable of withstanding operating temperatures of up to 900°C and exhibiting excellent stability in oxidizing and reducing environments. The electrochemical cell comprises three ceramic layers: an oxygen electrode, an electrolyte, and a hydrogen electrode where the hydrolysis of water into hydrogen takes place. This hydrogen electrode is made of a composite ceramic or metal-ceramic (also called cermet).

The electrolyte consists of a material exhibiting gas tightness (density greater than 95%, zero open porosity), good ionic conductivity (greater than 10-2 S.cm-1 at operating temperature), a coefficient of expansion close to that of the electrodes (the objective being to limit mechanical stresses), chemical inertness with respect to electrode materials, stability in oxidizing and reducing environments, and finally mechanical stability under operating conditions.

Regarding the electrodes, the chosen material must exhibit high electronic conductivity (greater than 100 S/cm) with, if possible, a degree of ionic conductivity to limit ohmic losses and delocalize the electrochemical reaction within the electrode volume. These electrodes are characterized by their high porosity, a property essential for the diffusion of water vapor, as well as for the removal of hydrogen at the cathode and oxygen at the anode. This porosity must be optimized to avoid local overpressures that tend to delaminate the electrode layers. More specifically, the hydrogen electrode requires both catalytic properties essential for water reduction and the ability to remain stable in a reducing environment. As for the oxygen electrode, it possesses catalytic properties for the oxidation of _O2- ions while remaining stable in ^an oxidizing environment.

With the aim of developing an economically viable process, it is important that all the materials constituting the electrochemical cells be available in large quantities and at low cost.

Object of the invention

One of the aims of the present invention is to propose a manufacturing process for electrode material of the electrochemical cell which addresses at least one of the aforementioned problems.

1. fourniture d’une résine comprenant un photoréactif polymérique, un solvant, et une charge comportant au moins un précurseur minéral de la céramique,
2. impression 3D de la résine selon un motif prédéterminé de sorte à former un squelette nanoarchitecturé poreux, et
3. frittage du squelette nanoarchitecturé poreux de sorte à obtenir une céramique nanoarchitecturée poreuse.

To this end, the present invention proposes a method for manufacturing a porous nano-architectural ceramic for an electrolyzer cell electrode, in particular for a high-temperature electrolyzer cell electrode, the method comprising the following steps:

1. supply of a resin comprising a polymeric photoreagent, a solvent, and a filler comprising at least one mineral precursor of the ceramic,
2. 3D printing of the resin according to a predetermined pattern to form a porous nano-architectural skeleton, and
3. sintering of the porous nano-architectural skeleton to obtain a porous nano-architectural ceramic.

The resin is typically a shear-thinning resin. The solvent is, for example, an organic solvent. The mineral precursor is typically YSZ, nickel/cerine, nickel/zirconia, other nickel derivatives, or titanates for a dihydrogen electrode, or a perovskite lanthanum derivative, such as LSM, LSC, LSCF, or an _Nd₂NiO₄ nickelate for a dioxygen electrode. The porous nanostructured backbone is, for example _, honeycomb-shaped or tetrakaidecahedral. The porous nanostructured ceramic is typically a ceramic oxide, a cermet, or a perovskite-structured ceramic.

This porous nano-architectural ceramic, thus fabricated, can be used as an electrode in the electrolyzer cell. This advantageously reduces material consumption compared to conventional electrodes, while simultaneously boosting their properties. Indeed, using 3D printing allows for the structuring of layers to create an optimal material architecture at the nanoscale, enabling a reduction in layer thickness and/or the amount of raw material required by developing more or less porous skeletons with mechanical strength equivalent to that of conventional ceramics. The porous nano-architectural skeleton can be developed and optimized by printing, for example, in a honeycomb or tetrakaidecahedral form (see the FIG. 1 ). It features increased porosity promoting the passage of water vapor while optimizing the number of triple points, leading to electrodes and cells with optimal properties.

The acronym YSZ in this document refers to yttrium oxide stabilized zirconium oxide or yttrium zirconia.

The acronym LSCF, as used in this document, refers to strontium-doped lanthanum ferrocobaltite._(1-x)Sr_xCo_(1-y)Fe_yO₃ LSM is strontium-doped lanthanum manganite of the La1-xSrxMnO3 type, and LSCo is lanthanum cobaltite.

Sintering offers an advantageous way to densify and stabilize the material. In one scenario, step c) of sintering is carried out at a temperature between 900 and 1600°C.

According to one provision, the duration of the sintering stage is between 1 and a few hours, in particular between 1 and 6 hours and for example 2 hours.

According to one possibility, the photoreactive polymer is chosen from acrylate-based resins, such as Polymethylmethacrylate (PMMA), and an organic solvent is of the acetone type.

According to one possibility, the porous nanoarchitecturally designed skeletons obtained in step b) can then be impregnated or doped with other materials in order to improve their physicochemical properties.

According to one provision, step b) of 3D printing is followed by step b') of pre-sintering, for example at a temperature between 500°C and 800°C, for a duration of between one and several hours, in particular about one hour, so as to allow the elimination of the polymeric photoreagent and, for example, residual organic solvent. Step b') of pre-sintering allows, in particular, the pyrolysis of said organic materials, resulting in their elimination with minimal residue.

In one possibility, the resin supplied in step a) further comprises a metallic precursor, mixed with the mineral precursor, such as NiO or nitrate salt in the case of a YSZ mineral precursor, or the resin supplied in step a) comprises a mineral precursor doped with the metallic precursor, such as coated nanoparticles (or "core shell nanoparticles" in Anglo-Saxon terminology), the nanoparticles being made of the mineral precursor material of the ceramic and the coating of the metallic precursor. This possibility leads to the formation of a cermet or a metal-ceramic that can be used in the fabrication of a dihydrogen electrode.

In one possibility, the resin supplied in step a) further comprises a metallic precursor, mixed with the mineral precursor, such as a La,Sr,Fe,Co nitrate or another nickelate-type oxide material when the mineral precursor is cerium oxide, or the resin supplied in step a) comprises a mineral precursor doped with the metallic precursor. This possibility leads to the formation of a material that can be used in the manufacture of a dioxygen electrode.

According to one provision, step a) includes the supply of a resin whose composition evolves during the 3D printing process to obtain a compositional gradient for the porous nano-architectural ceramic. This allows for adjustments to the concentration of the metallic precursor (or other material) in the resin, and/or the mineral precursor of the ceramic in the resin, to create one or more compositional gradients and optimize the porous nano-architectural ceramic for its intended application. It is then possible to fabricate buffer layers to manage the different coefficients of thermal expansion between the various constituent materials used, for example, between the support electrolyte material and that of an electrode.

According to one provision, the process includes, prior to step c), an impregnation step i) of the porous nanoarchitectural skeleton with an impregnation solution comprising at least the metallic precursor, in particular by immersing the porous nanoarchitectural skeleton in an impregnation solution, such as an impregnation solution comprising nitrate salt in water and at least one wetting agent, in particular intended to reduce the surface tension of the porous nanoarchitectural skeleton and ensure good infiltration (for example, a silicone base). This impregnation step i) constitutes another means of modulating the composition of the final porous nanoarchitectural ceramic in order to improve its properties.

According to one possibility, the impregnation step i) is carried out under vacuum, for several hours, for example between 1 and 12 hours.

According to one provision, the impregnation step i) is carried out at room temperature.

According to one variant, the impregnation step i) is carried out hot. Typically, the temperature can be between 20 and 50°C.

According to one possibility, at least one 3D printing parameter from step b) is modified during printing so as to vary the predetermined pattern, in order to modify the porosity of the porous nanoarchitectural skeleton.

Varying at least one of these 3D printing parameters can affect the shape and/or size of the cells in the porous nano-architectural skeleton.

According to one provision, at least one 3D printing parameter in step b) is gradually changed during printing so as to gradually vary the predetermined pattern.

According to one variant, at least one 3D printing parameter in step b) is changed in steps during printing so as to vary the predetermined pattern in steps.

This constitutes a new lever in the constitution of the electrode, or of the cell, according to the varied porosity requirements in the different constituent layers.

According to a second aspect, the invention proposes a method for producing an electrolyzer cell structure, in particular a high-temperature electrolyzer cell, the method comprising the following steps:

(l) supply of a supporting electrolyte,

m) fabrication of a dihydrogen electrode as previously described on a first face of the supporting electrolyte, and

n) fabrication of a dioxygen electrode as previously described on a second face opposite the first face of the supporting electrolyte.

According to a particular embodiment, the supporting electrolyte supplied in step l) comprises mainly, or is composed of, YSZ and the process includes, before the fabrication of a dihydrogen electrode according to step m), a formation step f) of a first intermediate layer comprising a 3D printing step, the intermediate layer comprising a decreasing concentration gradient in YSZ or CGO and an increasing concentration gradient in NiO away from the supporting electrolyte, until the composition of the porous nanoarchitectural skeleton for the dihydrogen electrode is obtained.

According to another particular embodiment, the process includes, prior to the fabrication of a dioxygen electrode according to step n), a step of formation f') of a second intermediate layer comprising a 3D printing step, the second intermediate layer comprising a decreasing concentration gradient of gadolinium oxide CGO (i.e. a doped cerine) and a concentration gradient of lanthanum derivative of perovskite structure, in particular in LSCF, in LSM, in LSC, or in nickelate of type Nd ₂ NiO ₄ , which is increasing away from the supporting electrolyte, until the composition of the porous nanoarchitectural skeleton for the dioxygen electrode is obtained.

According to a third aspect, the invention provides a porous nano-architectural ceramic for an electrolyzer cell electrode, obtained by the process described above, which comprises a pore volume to material volume ratio of between 30 and 70%. It is understood that said ceramic is a perovskite-structured lanthanum derivative for a dioxygen electrode and said ceramic is a metal-ceramic (or cermet) for a dihydrogen electrode.

Brief description of the drawings

Other features and advantages will become apparent upon reading the detailed description below, of a non-exhaustive example of implementation, made with reference to the attached figures in which:

FIG. 1 represents a schematic view illustrating a conventional electrolyzer cell of the prior art.

FIG. 2 represents a schematic view illustrating the different possibilities of porous nanoarchitectural ceramic obtained by 3D printing according to an embodiment of the invention.

FIG. 3 represents a schematic view of the manufacturing process of a porous nano-architectural ceramic according to a first embodiment of the invention.

FIG. 4 represents a schematic view of the manufacturing process of a porous nano-architectural ceramic according to a second embodiment of the invention.

FIG. 5 represents a schematic view of the manufacturing process of a porous nano-architectural ceramic according to a third embodiment of the invention.

FIG. 6 represents a schematic view of an electrochemical cell of an electrolyzer obtained by the manufacturing process of a porous nanoarchitectural ceramic according to an embodiment of the invention.

Detailed description

In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale to ensure clarity. Moreover, the different embodiments and variants are not mutually exclusive and can be combined.

Unless otherwise stipulated, the term "substantially" means, in this document, "exactly or to within 10% or to within 10°".

On the FIG. 1 An example of a conventional electrochemical cell 1 for a high-temperature electrolyzer is illustrated. Two metallic interconnectors (a) are present on either side of the cell 1 to make electrical contacts. The electrochemical cell 1 is made of ceramic and comprises an electrolyte labeled (b), a dioxygen electrode (d) labeled (d), and a dihydrogen electrode labeled (c) on either side of the electrolyte (b).

As illustrated in the FIG. 2 The present invention proposes an improved method for manufacturing said ceramics, particularly those constituting electrodes 3 and 4, by 3D printing. This technique makes it possible to use predetermined printing patterns leading to a nanostructured design, thereby increasing the porosity of the ceramic, reducing the amount of material required, while providing the same mechanical resistance and thermal cycling properties as conventional ceramics. It is thus possible to choose from a large number of architectures, such as stochastic cellular structures A of the closed-cell type B or open-cell type C, or non-stochastic cellular structures D comprising a two-dimensional network E or three-dimensional network F, in order to obtain the porous nanostructured ceramic 200 with the desired properties.

By “3D printing, we mean a three-dimensional printing method by additive manufacturing in successive passes, each pass comprising the deposition of a layer of resin, the deposited resin adhering to the resin of at least one previously deposited layer, the resin deposit at the level of each layer being controlled at each pass in such a way that the stacking of resin deposited during said successive passes constitutes the porous nanoarchitectural skeleton 300.

There FIG. 3 This illustrates an implementation of the process for manufacturing a NiO-YSZ dihydrogen electrode. It includes a step (a) of supplying a resin comprising a mixture of at least one photoreactive polymer (e.g., an acrylate-based resin such as Polymethyl Methacrylate, also known as PMMA), dissolved in an organic solvent (e.g., acetone), a mineral precursor of YSZ comprising a powder of a mixture of _ZrO₂ and _Y₂O₃ , and a metallic precursor, _NiO . The resin is then printed by a 3D printing device, for example, in a honeycomb pattern to form a porous nanoarchitectural skeleton (step (b)). A pre-sintering heat treatment, also known as 'debinding', is applied at a temperature of approximately 700-800°C to degrade the porous solvent and the photoreactive polymer, leaving only the inorganic materials in the nanostructured skeleton 300 (step b'). A sintering step at a temperature of approximately 1400°C (step c) is then applied to obtain a porous nanostructured metal-ceramic (or cermet) 200.

The second embodiment illustrated in the FIG. 4 This differs from the previous _one in that the mineral precursor of the ceramic used in the resin is directly doped with the metallic precursor, for example in the form of _ZrO₂ and _Y₂O₃ nanoparticles coated with NiO. 3D printing of the resin and application of the sintering heat treatment at approximately 1400°C results in a porous nano-architectural metal-ceramic with the same properties as those obtained previously.

A third embodiment is illustrated in the FIG. 5 In this implementation, the resin printed in step b) is free of metallic precursor filler. The resulting nanostructured skeleton 300 is impregnated with an aqueous nitrate salt solution under vacuum for 1 to 12 hours at room temperature. The sintering step then yields a porous nanostructured ceramic 200 with properties similar to those obtained previously.

These three implementation methods allow three different access routes to the same porous nanoarchitectural ceramic 200. They thus allow different access routes to the targeted ceramic, which expands the possibilities regarding the precursor materials that can be used.

According to a particular implementation method illustrated in theFIG. 6The invention is adapted to the manufacture of the electrolyzer cell 100 of an electrolyzer. To this end, the process includes the supply of a support electrolyte 2 made of dense YSZ ceramic (step 1). This support electrolyte 2 is used as a support for the manufacture of electrodes 3 and 4. A resin comprising a ZrO powder₂and Y₂O₃and NiO metal oxide is deposited by 3D printing onto one face of the support electrolyte 2 (step m). The 3D printing parameters change during the printing process to increase the porosity of the ceramic as one moves away from the support electrolyte 2, in order to achieve the desired porosity for the dihydrogen electrode 5. Similarly, the concentrations of the reagents in the resin supplied to the 3D printing device change during the printing process to create a compositional gradient from a yttrite content of 8 mol% to 3 mol% as one moves away from the support electrolyte 2, ultimately reaching the target composition for the dihydrogen electrode. 3. This allows the formation of a first intermediate layer 5 with an increasing porosity gradient and an increasing gradient in NiO content until the desired parameters for the nano-architectural metal-ceramic of the dihydrogen electrode are smoothly reached. 5 (step f). This first intermediate layer 5 acts as a buffer layer, absorbing the difference in the coefficient of thermal expansion within the structure during temperature changes, particularly during the sintering and cooling stages, and during the operation of the electrolyzer cell 100, thus limiting the risk of delamination. The first intermediate layer 5 also accommodates dimensional variations or changes in the printing pattern within the nanoarchitecture 200, which are implemented to ensure changes in porosity and which could weaken the cohesion of the three layers of the electrolyzer cell 100. A sintering treatment at 1400°C is then carried out to obtain the desired cermet 200.

Conversely, a second intermediate layer 6 is formed on the second face opposite the first face of the support electrolyte 2 (step f') in order to adapt the difference in thermal expansion between the material of the support electrolyte 2 and that of a thin barrier layer 6 in CGO (cerine oxide CeO2 substituted by gadolinium oxide _{Gd2O3 )} intended to prevent the reaction between the material for the dioxygen electrode 4 in LSCF and that of the support electrolyte 2. Thus, the second intermediate layer 6 is formed to understand a concentration gradient between the YSZ and the CGO and to prevent delamination between the layers of the electrolyzer cell 100.

Thus, the present invention makes it possible to obtain porous nanoarchitecturate ceramics 200 reducing the cost of raw materials while leaving a great deal of latitude to refine the parameters of composition, porosity and mechanical properties according to the needs targeted for the electrodes 3,4 of electrolyzer cells 100.

Claims (10)

A process for manufacturing a porous nano-architectural ceramic (200) to constitute an electrode for an electrolyzer cell (100), the manufacturing process comprising the following steps:

1. supply of a resin comprising a polymeric photoreagent, a solvent, and a filler comprising at least one mineral precursor of the ceramic,
2. 3D printing of the resin according to a predetermined pattern to form a porous nano-architectural skeleton (300), and
3. sintering of the porous nanoarchitectural skeleton (300) so as to obtain a porous nanoarchitectural ceramic (200).

Manufacturing method according to claim 1, wherein step b) of 3D printing is followed by a step b') of pre-sintering carried out so as to allow the removal of the polymeric photoreactive. A manufacturing process according to claim 1 or 2, wherein the resin supplied in step a) further comprises a metallic precursor, the metallic precursor being mixed with the mineral precursor, or the mineral precursor being doped with the metallic precursor. Manufacturing method according to claim 3, wherein step a) includes the supply of a resin whose composition evolves as the 3D printing progresses so as to obtain a composition gradient of the porous nanoarchitectural ceramic (200). Manufacturing process according to claim 3, which includes, prior to step c), an impregnation step i) of the porous nanoarchitectural skeleton with an impregnation solution comprising the metallic precursor. Manufacturing method according to any one of claims 1 to 5, wherein during step b), at least one 3D printing parameter is modified in such a way as to vary the predetermined pattern in order to modify the porosity of the porous nanoarchitectural skeleton (300). A method for producing an electrolyzer cell structure (100), comprising the following steps:
(l) supply of a supporting electrolyte (2),
(m) manufacturing a dihydrogen electrode (3) by implementing the manufacturing process according to any one of claims 1 to 6 on a first face of the supporting electrolyte (2), and
n) manufacturing of a dioxygen electrode (4) by implementing the manufacturing process according to any one of claims 1 to 6 on a second face of the supporting electrolyte (2), opposite to the first face. A production method according to claim 7, wherein the supporting electrolyte (2) supplied in step l) comprises predominantly, or is composed of, YSZ, and wherein the production method comprises, prior to step m), a step f) of forming a first intermediate layer (5) comprising a 3D printing step such that the first intermediate layer (5) comprises a decreasing concentration gradient of YSZ or CGO and an increasing concentration gradient of NiO away from the supporting electrolyte (2), until a desired composition of the porous nanoarchitectural skeleton (300) for the dihydrogen electrode is obtained. (3). A production method according to claim 7 or 8, comprising, prior to step n), a step f') of forming a second intermediate layer (6) comprising a 3D printing step such that the second intermediate layer (6) comprises a decreasing concentration gradient of CGO and a concentration gradient of a perovskite-structured lanthanum derivative increasing with respect to the supporting electrolyte (2), until the composition of the porous nanoarchitectural skeleton (300) for the dioxygen electrode is obtained. (4). Porous nanoarchitectural ceramic (200) for electrolyzer cell electrode (100) manufactured by implementing the manufacturing process according to any one of claims 1 to 6, wherein the ratio between the volume of pores and the volume of material is between 30% and 70%.