FR2872716A1 - REVERSIBLE DIHYDROGEN STORAGE PRODUCT, PROCESS FOR PRODUCTION THEREOF, AND USE OF SUCH A PRODUCT FOR THE REVERSIBLE STORAGE OF DIHYDROGEN - Google Patents

Abstract

The invention relates to a reversible molecular hydrogen storage product which comprises an active material which has hydrogen storage properties, and which comprises a catalytic material which is capable of adsorbing molecular hydrogen, and of dissociating the molecular hydrogen in hydrogenated species, characterized in that the active material comprises a rare earth oxide.The invention also relates to a method of manufacturing such a storage product.The invention also relates to the use of such a product. storage.

Description

"Reversible storage product of dihydrogen, process for

  BACKGROUND OF THE INVENTION The invention relates to a reversible storage product of molecular hydrogen.

  The invention more particularly relates to a reversible storage product of molecular hydrogen which comprises: - an active material which has hydrogen storage properties; a catalytic material which is capable of adsorbing molecular hydrogen, and of dissociating molecular hydrogen into hydrogenated species.

  The invention also relates to a method of manufacturing such a storage product.

  The invention finally relates to the use of such a storage product or a storage product obtained by the manufacturing process.

  Power generation devices using hydrogen as fuel are currently undergoing many developments, in particular to replace the hydrocarbon-based fuels which are alleged to be pollutants.

  Thus, fuel cells are devices that are capable of producing electricity from hydrogen stored in storage means and from oxygen contained in atmospheric air.

  The residues of the operation of a fuel cell consist mainly of water. The fuel cell is therefore particularly low polluting.

  Thus, it attempts to equip motor vehicles such fuel cells to supply electricity to an electric propulsion engine of the vehicle to replace traditional gasoline or diesel engines.

  In addition, the fuel cell coupled with a hydrogen reservoir forms a device capable of achieving a high energy density, and in particular to have a great autonomy of operation. Thus, many other applications are possible such as powering computers or mobile phones.

  However, the autonomy of operation depends mainly on the capacity of the hydrogen storage means. Various storage means are known which can store hydrogen in various forms. However, the known hydrogen storage means have many disadvantages.

  The storage of hydrogen in gaseous form in a reservoir is thus known. In order for the quantity of hydrogen thus transported to be sufficient, it is necessary to store hydrogen gas under pressure. However, this form of storage is impractical because it requires heavy tanks that are supposed to withstand the pressure. In addition, in gaseous form at high pressure, the explosive nature of hydrogen is exacerbated. Storage of gaseous hydrogen under pressure is not only cumbersome but also dangerous.

  The storage of hydrogen under 1 atm and in liquid form is also known. To maintain the hydrogen in liquid form, it is necessary to cool it to an extremely low temperature, for example at -253 C. However, the maintenance of hydrogen at such a temperature is very expensive in energy and requires a device for cumbersome cooling.

  To solve these problems, it is known to store hydrogen by creating a partial ionic bond within a chemical storage compound, such as metal hydrides.

  These chemical storage compounds are capable of adsorbing a very large quantity of hydrogen. The storage volume capacity is thus higher than in the previous storage means.

  However, if the performance in volume capacity of known storage chemical compounds are exceptional, other technical and financial problems do not allow to consider their industrial development in large series.

  These compounds are thus expensive to manufacture, especially because they have expensive components.

  In addition, the storage and / or destocking operations in known storage chemical compounds require the latter to be heated to elevated temperatures. Therefore, their use in portable devices such as mobile phones, then suppose the addition of many elements that are likely to increase the size of portable devices, making them less competitive.

  The object of the present invention is to solve these problems by proposing a product which is inexpensive to manufacture and which is capable of reversibly storing molecular hydrogen under conditions close to normal conditions of temperature and pressure. The storage product of the type described above is thus characterized in that the active material comprises a hydroxylated metal oxide.

  According to other features of the invention: the active material has a crystalline structure of fluorite type; the active material comprises hydroxylated rare earth oxide; the active material comprises hydroxylated cerium dioxide; the catalytic material comprises a material of the nickel metal (Ni) type; - its chemical formula is (CeO2) Ni; the catalytic material comprises platinum and / or palladium and / or gold and / or rhodium and / or copper and / or silver; the active material forms a core which carries particles of the catalytic material on its surface; the storage product is in the form of a powder, each grain of which comprises a core of active material and a surface of catalytic material; the storage product has a specific surface whose area is between 50 m 2 / g and 200 m 2 / g; The invention also relates to a method for manufacturing a reversible storage product of molecular hydrogen as described above, characterized in that it comprises a step of activating the storage product which comprises a first phase during which the storage product is heated to an activation temperature of the active material under a reducing atmosphere, and a second conditioning phase during which the storage product is heated to a desorption temperature under vacuum or in a virgin atmosphere. oxidizing species.

  According to other characteristics of the manufacturing process: the activation temperature is greater than a first lower limit temperature beyond which the catalytic material is converted to a purely metallic phase, and in that the activation temperature is lower than at a second upper limit temperature beyond which the ionic conductivity of the active material is substantially decreased; the activation temperature is between 200 ° C. and 500 ° C. the desorption temperature is less than or equal to the activation temperature; at the end of the first phase, the storage product is cooled from the activation temperature to an ambient temperature of approximately 25 ° C .; in the first phase, the product is kept at the activation temperature for a period of time which is between 1 hour and 24 hours; in the second conditioning stage, the product 5 is maintained at the desorption temperature for a period of time which is between 1 hour and 24 hours; the manufacturing method comprises a first prior step of obtaining an inactivated storage product comprising a catalytic material having catalytic properties of dissociation of molecular hydrogen and comprising a material having atomic hydrogen conduction properties when it is activated; the first step comprises a co-precipitation phase during which a rare earth salt is co-precipitated with another metal salt in a basic solution; the rare earth salt is cerium nitrate Ce (NO3) 3.6H2O, and in that the metal salt is nickel nitrate Ni (NO3) 2.6H2O.

  The invention also relates to the use of the storage product according to the invention or of a product obtained by the manufacturing method according to the invention for the reversible storage of molecular hydrogen.

  According to other characteristics of the use of this storage product: the use comprises a first storage operation during which the product is heated to a storage temperature which is lower than the activation temperature under an atmosphere comprising dihydrogen; the storage temperature is between 0 ° C. and the activation temperature. During the storage operation, the storage product is subjected to a pressure of between 0.5 bar and 10 bar; - The use comprises a destocking operation of the hydrogen during which the storage product is heated to a destocking temperature which is less than or equal to the activation temperature, under vacuum or virgin atmosphere of oxidizing species; the destocking temperature is between 25 C and the activation temperature.

  Other features and advantages will become apparent during the reading of the detailed description which follows.

  In known manner, the hydrogen storage product comprises an active material having ionic conduction properties. The active material is thus capable of storing hydrogen in the form of hydrogenated species. Advantageously, the active material is constituted by a crystalline structure of "fluorite" type which is very conducive to such use.

  The active material has an interface with particles of a surface catalytic material which has the property of capturing or adsorbing dihydrogen molecules (H2) and dissociating the hydrogen atoms to form hydrogenated species.

  The catalytic material also has the property of being able to reconstitute a molecule of dihydrogen from the hydrogenated species.

  According to an advantageous form of the invention, the storage product is a nano-composite material in powder form.

  For each grain of powder, the active material forms a core which is lined with a more or less dense envelope of particles of catalytic material.

  However, the storage product is not limited to this form "cceurenveloppe", the essential is that the catalytic material has at least a surface portion exposed to the gas to be loaded and that the storage product has an interface between the material catalytic and active material.

  The storage capacity of the storage product is proportional to the volume of the active core.

  In order to promote the interactions with the gas to be stored, that is to say the hydrogen (H 2), the surface of the product has a high specific surface area, for example between 50 and 200 m 2 / g.

  According to the teachings of the invention, the active material is a metal oxide.

  This is a rare earth oxide, and more particularly cerium oxide CeO2. Indeed, CeO2 has a crystalline structure of the "fluorite" type which makes it possible to store a large quantity of hydrogenated species. In addition, this element is an inexpensive material.

  It is more particularly a core formed of hydroxylated cerium oxide which has ionic conduction properties quite surprising and adapted to a storage use of hydrogenated species.

  To simplify the reading of the description, the term "hydroxylated cerium oxide" will be referred to as "CeO2".

  The catalytic material here consists of nickel metal Ni which has the required catalytic properties. However, the catalytic material may also consist of other catalytic materials, among which are platinum, palladium, gold, copper, silver or rhodium.

  Nickel Ni, however, has the advantage of being inexpensive compared to the examples cited, and has the advantage of being reactive with molecular hydrogen under standard conditions of pressure and temperature (1 bar, 25 C). .

  Thus, a storage product of formula (CeO 2) Ni has the advantage of being inexpensive to manufacture.

  Such a storage product can be obtained by the following manufacturing process. This manufacturing process mainly comprises a first step El obtaining an inactive product, then a second step E2 activation of the product obtained in the first step.

  The manufacturing method is described for the manufacture of a storage product whose core is made of CeO2 and whose surface is made of Ni, the surface having an interface with the core. But it is of course possible to adapt the implementation methods, including different temperatures, depending on the materials used.

  The first step of obtaining El comprises a first phase El1 synthesis of the inactive product.

  According to a preferred embodiment of the first synthesis phase El 1, the inactive product is obtained by a method known as "coprecipitation".

  Nitrate salts Ce (NO3) 3.6H2O and Ni (NO3) 2.6H2O are dissolved in distilled water (concentration between 100 gL "and 200 gL-1) Nitrates are co-precipitated in a pH solution basic, for example potassium hydroxide (KOH) concentrated to 100 μL or triethylamine (TEA).

  The precipitate thus obtained is filtered and washed. The washing of the precipitate is carried out here with boiling distilled water until the pH of the washing water is neutral, that is to say a pH of about 7.

  During a second phase E12 of the first manufacturing step E1, the precipitate is dried.

  The washed precipitate is suspended in a container containing ethanol. The container is then immersed in an ultrasonic apparatus. The ethanol and the precipitate in suspension are mixed for example by a mechanical stirrer for a period of 12 hours. The precipitate in suspension is thus perfectly dispersed in ethanol.

  The mixture thus obtained is then cooled in liquid nitrogen for one hour to obtain a solid block.

  The solid block is then introduced into a desiccator which is placed under a primary vacuum. The solid block is dried under these conditions at 25 C for 24 hours.

  At the end of this drying phase E12, an inactive product powder is thus obtained whose surface has a specific surface area of between 50 and 200 m 2 / g.

  This desiccation phase E12 makes it possible to obtain a more efficient storage product, and in particular by improving the surface state of the inactive product. However, this E12 phase can be carried out according to other procedures.

  At the end of the first step of obtaining E1, an inactive product is obtained in the form of a powder which comprises at least two crystalline phases: hydroxylated CeO 2 and Ni (OH) 2. This inactive product already has the structure of the final storage product "core I surface" as described above. However, the hydroxylated CeO 2 core is not activated, in addition the nickel is not yet present in the form of nickel metal Ni.

  It is important that the specific surface area of the powder is large in order to promote the interaction of each grain of powder with the gas to be stored, in this case with hydrogen (H2), as explained later in the description. The first manufacturing step El described above, and in particular the synthesis phase ElI using the co-precipitation method, makes it possible to obtain a powder having a specific surface whose area is of the order of 100 m 2 / g.

  The second activation step E2 comprises a first phase E21 during which the actual activation of the storage product is carried out under a reducing atmosphere containing, in particular, hydrogen H 2 and a second conditioning phase E 22 during which the The storage product is "emptied" of the hydrogen it contains in order to make it operational for a hydrogen storage operation.

  The first phase E21 is intended to "activate" the heart, here the hydroxylated CeO 2, of the storage product, that is to say to enable it to adsorb or retain a "large" quantity of hydrogen reversibly in temperature and pressure conditions close to normal conditions, i.e. at a temperature of about 25 ° C and a pressure of about 1 bar.

  A second function of this phase E21 is to convert the catalytic material Ni (OH) 2 to nickel metal Ni.

  During this first phase E21, the inactive product obtained in the first step E1 is heated to an activation temperature under a reducing atmosphere, and especially under an atmosphere consisting of pure hydrogen or diluted in a neutral atmosphere. The storage product is for example heated at a rate or heating rate of 10Cmin-1.

  Then the storage product is maintained at the activation temperature. For example, the hold time at the activation temperature may vary between 1 hour and 24 hours.

  In this case, the activation temperature is between 200 ° C. and 500 ° C. In order to convert the catalytic material of the Ni metal nickel storage product, it is necessary to heat the storage product above a temperature of 200 ° C. C. On the other hand, if the activation temperature exceeds 500 C, the ionic conduction properties of the hydroxylated CeO 2 core of the storage product are substantially reduced.

  Preferably, the activation temperature must even be kept below 450 C for the storage product to have an optimal storage capacity.

  Then the temperature is gradually decreased to an ambient temperature of about 25 C, for example at a rate or heating rate of 20Cmin-1 still under the same reducing atmosphere.

  During the second conditioning phase E22, the storage product thus activated is then "emptied" of all the hydrogenated species which have been adsorbed during the charging phase E21 so as to make it operational before carrying out the subsequent operations of load under optimal conditions.

  Thus, the storage product is again heated but in a virgin atmosphere of hydrogen and oxidizing species, for example under argon or helium or under vacuum.

  The storage product is here heated at a rate or heating rate of 10Cmin-1 to a so-called desorption temperature which is less than or equal to the activation temperature.

  The desorption temperature is, for example, between 200 ° C. and 500 ° C., and preferably between 200 ° C. and 450 ° C.

  The storage product is then maintained at this desorption temperature for a time long enough for the hydrogenated species that the product had previously adsorbed to be desorbed, for example between 1 hour and 24 hours.

  At the end of this conditioning phase E22, the storage product is cooled to 25 ° C. at a rate or heating rate of 20 ° C., always under a virgin atmosphere of hydrogen and oxidizing species.

  This last phase E22 thus makes it possible to obtain the storage product 20 in the final form of a powder whose chemical formula is (CeO 2) Ni.

  The invention proposes to use the product thus obtained for an application for the reversible storage of molecular hydrogen or dihydrogen.

  Thus, during a storage or charging operation of hydrogen in the storage product, the storage product is maintained at a storage temperature which is between 0 ° C. and the activation temperature (200 ° C.). 500 C) during a storage stage under an atmosphere of pure dihydrogen or diluted in a neutral atmosphere.

  During this storage stage, the storage temperature is preferably between 25 ° C. and the activation temperature. The storage pressure to which the storage product is subjected during storage can be between 0.5 bar and 10 bar, but it is preferably between 0.8 bar and 5 bar.

  During this operation, the dihydrogen molecules are adsorbed by nickel Ni which, by its catalytic properties, dissociates the dihydrogen molecules into hydrogen ions. These hydrogen ions are then adsorbed by the core, that is to say that they migrate to the inside of the hydroxylated CeO 2 core by virtue of the ionic conduction properties of the latter. As long as the heart is not "full", that is to say as long as there are spaces not occupied by hydrogenated species, it is possible to fill the storage product.

  The storage rate of hydrogen in the storage product increases as storage temperature and / or storage pressure increases.

  Advantageously, however, it is also possible to store hydrogen at low temperatures and pressures. Thus, even if the "filling" time of the storage product is lengthened, the energy required for the storage operation is advantageously very small.

  In general, the storage product must not be subjected to temperature and pressure conditions capable of transforming the catalytic material or of reducing the ionic conduction properties of the active material. For this purpose, it will be avoided, for example, to heat the storage product beyond the activation temperature.

  The duration of the storage stage may be variable depending on the amount of hydrogen that we want to store. The amount of hydrogen stored depends on the heating time and the storage temperature. Thus, the amount of stored hydrogen increases as the duration of the storage stage increases until a stable amount of stored hydrogen is obtained corresponding to the saturation of the hydrogen storage product.

  Thus, by way of example, results of experiments carried out on a sample of storage product exposed to a pressure of 1 bar under a dihydrogen atmosphere diluted to 95% in helium and at a storage temperature of 250.degree. C, are given in Table 1 below.

  Duration of the step of 0.16 1 2 4 6 8 storage (h) Relative quantity 1 1, 5 2 3.8 4 4.2 stored hydrogen

Table 1

  When the storage product is thus "filled" with hydrogen, it is possible to destock the hydrogen by again exposing the "filled" storage product under certain conditions of temperature and pressure, during a destocking operation or discharge.

  During the destocking operation, the "filled" storage product is heated to a destocking temperature of between 25.degree. C. and the activation temperature during a destocking stage under a hydrogenated atmosphere and / or under an atmosphere neutral or vacuum. This heating causes the desorption in the form of gas of the majority of the adsorbed hydrogen during the charging operation.

  Preferably, the destocking temperature is greater than or equal to 100 C. It is also possible to vary the destocking pressure to lower the destocking temperature below 100 C while maintaining a satisfactory retrieval rate.

  The hydrogen ions stored in the core of the storage product then migrate to its surface. In contact with nickel Ni, the hydrogen ions reform gaseous dihydrogen molecules.

  Thus, by way of nonlimiting example, Table 2 presents results of destocking operations conducted on a sample of storage product "filled" during a prior storage operation. In this example, the preliminary storage operations lasted 2 hours under a pressure of 1 bar and under a hydrogen atmosphere diluted to 95% in helium. Each prior storage operation took place at a storage temperature different from 50 C, 150 C and 250 C.

  Temperature of 50 C 150 C 250 C Storage Quantity of hydrogen 1,4 1,9 1,0 relative destocked

Table 2.

  The storage product is for example capable of desorbing at least 0.7 g of molecular hydrogen per 100 g of product.

  The storage product is likely to undergo several cycles of storage / destocking.

Claims (25)

  1. A reversible molecular hydrogen storage product which comprises: an active material that has hydrogen storage properties; a catalytic material that is capable of adsorbing molecular hydrogen and dissociating molecular hydrogen into hydrogenated species; characterized in that the active material comprises hydroxylated metal oxide.   2. Storage product according to any one of the preceding claims, characterized in that the active material has a crystalline structure of fluorite type.   3. Storage product according to the preceding claim, characterized in that the active material comprises hydroxylated cerium dioxide.   4. Storage product according to any one of the preceding claims, characterized in that the catalytic material comprises a nickel metal material (Ni).   5. Storage product according to the preceding claim, characterized in that its chemical formula is (CeO2) Ni Storage product according to one of the preceding claims, characterized in that the catalytic material comprises platinum and / or palladium and / or gold and / or rhodium and / or copper and / or money.   7. Storage product according to any one of the preceding claims, characterized in that the active material forms a core which carries on its surface particles of the catalytic material.   8. Storage product according to any one of the preceding claims, characterized in that it is in the form of a powder, each grain comprises a core of active material and a catalytic material surface.   9. Storage product according to the preceding claim, characterized in that it has a specific surface whose area is between 50 m2 / g and 200 m2 / g.   10. A method of manufacturing a reversible storage product of molecular hydrogen according to any one of claims 1 to 9, characterized in that it comprises a step (E2) of activation of the storage product which comprises a first a phase (E21) in which the storage product is heated to an activation temperature of the active material under a reducing atmosphere, and a second conditioning phase (E22) during which the storage product is heated to a temperature desorption under vacuum or in a virgin atmosphere of oxidizing species.   11. Method according to the preceding claim, characterized in that the activation temperature is greater than a first lower limit temperature beyond which the catalytic material is converted into a purely metallic phase, and in that the activation temperature is less than a second upper limit temperature beyond which the ionic conductivity of the active material is substantially decreased.   12. Method according to the preceding claim, characterized in that the activation temperature is between 200 C and 500 C.   13. Method according to any one of claims 10 to 12, characterized in that the desorption temperature is less than or equal to the activation temperature.   14. Method according to any one of claims 10 to 13, characterized in that at the end of the first phase (E21), the storage product is cooled from the activation temperature to an ambient temperature of about 25 C.   15. Method according to any one of claims 10 to 14, characterized in that during the first phase (E21), the product is maintained at the activation temperature for a period of time which is between 1 hour and 24 hours.   16. Method according to any one of claims 10 to 15, characterized in that during the second conditioning step (E22), the product is maintained at the desorption temperature for a period which is between 1 hour and 24 hours .   17. Method according to any one of claims 10 to 16, characterized in that it comprises a first prior step of obtaining an inactivated storage product comprising a catalytic material having catalytic properties of dissociation of molecular hydrogen and comprising a material having conduction properties of atomic hydrogen when activated.   18. Method according to the preceding claim, characterized in that the first step comprises a co-precipitation phase during which a rare earth salt is co-precipitated with another metal salt in a basic solution.   19. Method according to the preceding claim, characterized in that the rare earth salt is cerium nitrate Ce (NO3) 3.6H20, and in that the metal salt is nickel nitrate Ni (NO3) 2.6H20.   20. Use of the storage product according to claims 1 to 9 or a product obtained by the manufacturing method according to claims 10 to 19 for the reversible storage of molecular hydrogen.   21. Use according to the preceding claim, characterized in that it comprises a first storage operation during which the product is heated to a storage temperature which is lower than the activation temperature in an atmosphere comprising dihydrogen.   22. Use according to the preceding claim, characterized in that the storage temperature is between 0 C and the activation temperature.   23. Use according to any one of claims 21 to 22, characterized in that during the storage operation, the storage product is subjected to a pressure which is between 0.5 bar and 10 bar.   24. Use according to any one of claims 21 to 23, characterized in that it comprises a deoxidizing operation of the hydrogen during which the storage product is heated to a destocking temperature which is less than or equal to the activation temperature, under vacuum or under virgin atmosphere of oxidizing species.   25. Use according to the preceding claim, characterized in that the destocking temperature is between 25 C and the activation temperature.