WO2010029407A1

WO2010029407A1 - Hydrogen store

Info

Publication number: WO2010029407A1
Application number: PCT/IB2009/006787
Authority: WO
Inventors: Ferdi SCHÜTH; Michael Felderhoff; Borislav Bogdanovic; Weidenthaler Claudia; Andre Pommerin
Original assignee: Studiengesellschaft Kohle Mbh
Priority date: 2008-09-12
Filing date: 2009-09-08
Publication date: 2010-03-18
Also published as: WO2010029407A8; DE102008047222A8; DE102008047222A1

Abstract

A hydrogen store comprising a metal hydride and a pressure-rated container, wherein the metal hydride is selected from among low-temperature hydrides of the general formula Me¹ _x(Al_yH_z)_n(I), Me is selected from among Sc, Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, La, Ce, Pr and Nd or when x ≥ 2 can also be a mixture of a plurality of metals, x is from 1 to 3, y is from 1 to 2, z is from 4 to 7 and n is from 1 to 7, is claimed. The use of complex low-temperature hydrides of the formula (I) enables the storage capacity of hydrogen stores to be increased significantly, so that the range in automotive applications can be improved at a reduced weight of the store.

Description

Hydrogen storage

The invention relates to a hydrogen storage, comprising a metal hydride and a pressure-resistant container.

State of the art

Along with the advances in fuel cell development for mobile and stationary systems, the need to store sufficiently large quantities of hydrogen, especially in the automotive field, is becoming increasingly apparent. In addition to the physical methods of hydrogen storage (high pressure, low temperature), the hydrogen can also be stored in chemical form in a hydride-forming alloy or chemical compound. Examples of typical hydride-forming alloys are TiFe or C14-Laves phases hydrides, which have a storage capacity of about 1.5% by weight of hydrogen, based on the hydride-forming alloy. Although complex metal hydrides, such as NaAlH ₄ , have significantly higher hydrogen storage capacities (NaAlH ₄ 5.6 wt%), they also need to be significantly increased to ensure a sufficiently long range for mobile applications. A negative effect of the latter systems is that additional technical equipment such as heat exchangers for releasing the hydrogen from the complex metal hydride are necessary. As a result, the effective storage capacity, based on the overall system, additionally reduced. So far, none of these methods can provide a sufficient amount of hydrogen at acceptable volumetric and gravimetric storage density for automotive applications.

Patent DE 35 14 500 discloses a process for storing hydrogen under a pressure of 100-300 bar in combination with a hydride-forming alloy. As hydridbildende alloys TiFe or C14 Lavesphasen hydrides are called, which can store a maximum of 1.9 wt.% Hydrogen. In addition to the hydride-forming alloy, the free gas volume within the storage tank should also be used for hydrogen storage. Even with this system, the achievable storage capacities are not sufficient to ensure high ranges for mobile systems (automobiles). Rather, the gravimetric storage densities of the overall system are in the order of only 1 wt .-%. That alone weighs that

Hydrogen storage system approx. 500 kg for the storage of approx. 5 kg of hydrogen.

The object of the invention was to optimize the weight-related storage capacity for hydrogen. As a result, based on the weight unit of storage, more hydrogen than previously stored.

The present invention is a hydrogen storage comprising a metal hydride and a pressure-resistant container, characterized in that the metal hydride is selected from low temperature of the general formula I.

Me ¹ _x (Al _y H _z ) _n (I) in the

Me ^{1 is} selected from Sc, Ti, Zr, V ₁ Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, La, Ce, Pr and Nd, or when x> 2, also a mixture may be of several metals, and x is a number from 1 to 3, y is a number from 1 to 2, z is a number from 4 to 7 and n is a number from 1 to 7.

Surprisingly, it has now been found that by using complex low-temperature hydrides of the general formula Me ¹ _× Al _y H _z, the storage capacity of hydrogen stores can be significantly increased. This not only reduces the weight of the memory, but also the range in automotive applications is increased.

Cryogenic hydrides are generally understood as meaning those hydrides which have an equilibrium hydrogen pressure ≥ ¹ bar at temperatures 50 ≥T ≥ -30 ° C. Expanding the definition of Buchner, complex low-temperature hydrides are understood to mean those compounds whose hydrogen equilibrium pressure is significantly greater than 1 bar at room temperature, preferably between 50 and 900 bar. For example, complex aluminum metal hydrides are those compounds consisting of hydride ions, an aluminum metal (AI) and at least one electropositive metal (Me). They have the general form Me ¹ _x Al _y H _z . Thus, such hydrides are not thermodynamically stable under standard conditions (298 K, 1 bar), but can only be produced in a pressure vessel under elevated hydrogen pressure (> 50 bar). As complex metal hydrides, for example metal-aluminum hydrides (metal alanates) can be used, which have a gravimetric storage densities up to 9 wt.% Hydrogen. Some examples of complex metal-aluminum hydrides with their hydrogen storage densities are shown in Figure 1. The list is exemplary and not to be considered as complete. Generally, those electropositive metals are used which are selected from the metals of the subgroups of the periodic table as well as the rare earth metals.

In the context of the present invention, in addition to the complex low-temperature hydrides, it is also possible to use alkali metal and / or alkaline-earth aluminum hydrides (alkali metal or alkaline earth metal anates) of the general formula II

Me ² _a (Al _b H _c ) _m (II) in the

Me ^{2 is} selected from Li, Na, K, Mg and Ca, or when x> 2, may also be a mixture of several metals, and a is a number from 1 to 3, b is a number from 1 to 2, c is a number from 4 to 7 and m is a number from 1 to 7, may be included. As an example, the complex metal-aluminum hydride compound CaAIH _{5 may} be mentioned here. In addition to the simple complex aluminum hydrides, mixed complex aluminum hydrides can also be used. The compound NaMg (AIH ₄ J _{3 is} listed as an example. Good storage capacities can be obtained if the complex low-temperature hydrides and the complex alkali metal and / or alkaline earth aluminum hydrides are present in a ratio of 10 mol% to 90 mol% to 90 mol% to 10 mol%. available.

When low temperature hydrides and the alkali and / or alkaline earth aluminum hydrides are used together in the hydrogen storage of the present invention, it is believed that these two types of compounds can form mixed aluminum hydrides from mixtures of alkali, alkaline earth, transition and / or rare earth metals, i. can no longer be detected as separate compounds.

A further increase in the storage capacity can be achieved, for example, by virtue of the fact that the pressure-tight container has a size in addition to the storage materials, such as a hydrogen-storing complex metal hydride or a hydride-forming metal or a hydride-forming alloy has free volume, which can be used in the high-pressure tank for storing hydrogen.

The basic pressure curve for the removal of hydrogen is shown in Figure 2. At a loading pressure of 350 bar, the pressure in the high-pressure tank decreases until the equilibrium pressure at 200 bar of the cryogenic hydride has been reached (A). During hydrogen extraction, the pressure remains constant until all of the metal hydride is completely decomposed (B). After complete decomposition, the pressure drops on further withdrawal to 0 bar (C).

The storage capacity of such a tank system is exemplified in the following description.

With an internal volume of the pressure vessel of 100 L, 60 kg of a room temperature unstable hydrogen storage compound of the type Ti (AlH ₄ J ₄ having an assumed equilibrium pressure of 200 bar and a density of 1 g / cm ³ are used L free volume due to interstices of the particles of the storage material and other free gas volumes within the pressure vessel available.

When the hydrogen is removed, the pressure in the system falls until the equilibrium pressure of the low-temperature hydride has been reached (area A in Figure 2). In this area about 0.50 kg of hydrogen can be stored. In area B, the unstable metal hydride decomposes upon further hydrogen abstraction. The pressure in the system remains almost constant during the decomposition of the unstable metal hydride. 5.58 kg of hydrogen are stored in this area. As the hydrogen is withdrawn, the pressure drops from 200 to 0 bar (range C). 0.67 kg are stored in this area. The total amount of hydrogen that can be stored for such a system is 6.75 kg of hydrogen.

In a comparable pressurized gas system of 100 L volume, at a pressure of 350 bar, only 2.9 kg of hydrogen (calculated for ideal behavior) can be stored. This is less than half achievable with a storage system of the combination of unstable metal hydride and high pressure.

Since only low-temperature hydrides are used as storage material for the hydrogen tank, eliminating the need for an external heat supply in many cases Decomposition of the hydrogen storage material, as is necessary with complex hydrides of the type of NaAlH ₄ or high temperature metal hydrides such as MgH ₂ . As a result, the structural design of the entire storage system simplified considerably.

When using a high pressure tank system with an unstable hydride compound in combination with a fuel cell system, the high hydrogen pressure in the tank system at any time a sufficiently large form for the operation of the fuel cell is available. In the case of PEM (PEMFC) fuel cells, this is in the region of 5 bar and thus significantly below the operating pressure of the hydrogen storage system.

By simple pressure measurement in the tank system, the remaining degree of filling can be determined towards the end of emptying (C).

According to the invention, the storage of hydrogen is carried out for the most part in a complex cryogenic metal hydride at a hydrogen pressure which is between 50 and 900 bar, in particular between 50 and 350 bar hydrogen pressure.

Usually, the storage takes place in a pressure vessel. In a preferred embodiment, pressure vessels made of composite materials, for example carbon fiber wrapped metal vessels, are used. The pressure-resistant container should be designed so that it can be pressurized to a pressure of 50 to 900 bar

In a further preferred embodiment, such pressure vessels are used, which have an integrated heat exchanger, so that the released during loading reaction and compression heat can be dissipated.

In a further preferred embodiment, such pressure vessels are used which contain a highly porous metal foam for better heat exchange. For producing such metal foams, composites of a metal and a blowing agent (often titanium hydride) are generally used. After compression to a starting material, this is heated to a temperature above the melting point of the metal used. In the process, the metal hydride decomposes, releases hydrogen and foams the mixture. This metal foam may consist of aluminum, aluminum alloys or other porous metal foams. Another object of the present invention is a process for storing hydrogen in which a metal alloy capable of forming metal hydrides of general formula I is formed

Me ¹ _x (Al _y H _z ) _π (I)

in the

Me is selected from Sc, Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, La, Ce, Pr and Nd, or when x> 2, also a mixture of may be a plurality of metals, x is a number from 1 to 3, y is a number from 1 to 2, z is a number from 4 to 7 and n is a number from 1 to 7, is pressurized in a pressure vessel under pressure with hydrogen.

Another object is a method for releasing hydrogen, in which a metal hydride of the general formula I.

Me _x (Al _y H _z ) _n (I)

in the

Me is selected from Sc, Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn ₁ Y, Nb, Mo, La, Ce, Pr and Nd, or when x> 2, also a mixture of a number from 1 to 3, y is a number from 1 to 2, z is a number from 4 to 7 and n is a number from 1 to 7, is kept under hydrogen pressure in a pressure vessel, and the release of the

Hydrogen occurs by reducing the pressure.

In a preferred embodiment, the inventive method for storing hydrogen is used. In this embodiment, aluminum metal and one or more other metals or metal hydrides are used as the solid starting compounds and H _{2 is used} under high pressure as the gaseous component, wherein the storage of hydrogen takes place in solid form in a complex metal aluminum hydride. In addition to the complex aluminum hydride compounds described, other complex metal hydrides (eg transition metal borohydrides) can also be used as the hydrogen storage material. The prerequisite is that their hydrogen equilibrium pressure is between 50 and 900 bar at room temperature.

In a further preferred embodiment, in addition to aluminum and individual metals, metal alloys or metal mixtures are used to form the metal (mixture) aluminum hydride.

In a further embodiment of the process according to the invention, catalysts, preferably transition metal catalysts, are added to the reaction mixture. These catalysts improve the hydrogenation and dehydrogenation properties of the hydrogen storage materials. The catalysts can be added to the storage material in the form of metals, metal compounds or as alloy constituents of the metals used.

Preferably, the transition metal catalysts are selected from transition metal compounds of the group B to VB of the periodic table as well as Fe, Co, Ni and compounds of rare earth metals or combinations thereof, in particular their alkoxides, halides, hydrides, organometallic and intermetallic compounds, such as TiAl. ₃

Claims

claims

1. hydrogen storage comprising metal hydride and a pressure-resistant container, characterized in that the metal hydride is selected from low temperature of the general formula

Me ¹ _x (Al _y H _z ) _n (I) in the

Me ^{1 is} selected from Sc ₁ Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu ₁ Zn, Y, Nb, Mo, La, Ce, Pr and Nd, or when x> 2, also a mixture may be of several metals, and x is a number from 1 to 3, y is a number from 1 to 2, z is a number from 4 to 7 and n is a number from 1 to 7.

2. Hydrogen storage according to claim 1, characterized in that one or more further metal hydrides selected from alkali metal and alkaline earth metal hydrides of the general formula II

Me ² _a (Al _b H _c ) _m (II) in the

Me ^{2 is} selected from Li, Na, K, Mg and Ca, or when x> 2, it may also be a mixture of several metals, and a is a number from 1 to 3, b is a number from 1 to 2, c is a number from 4 to 7 and m is a number from 1 to 7, are included

3. hydrogen storage according to claim 1 or 2, characterized in that the cryogenic hydrides and the alkali and / or alkaline earth metal hydrides present in a ratio of 10 mol% to 90 mol% to 90 mol% to 10 mol%.

4. hydrogen storage according to one of claims 1 to 3, characterized in that the metal hydride has a gravimetric storage capacity> 5 wt .-%.

5. hydrogen storage according to one of claims 1 to 4, characterized in that the hydrogen equilibrium pressure of the metal hydrides having the general formula I at room temperature between 50 and 900 bar

6. hydrogen storage according to one of claims 1 to 5, characterized in that the container can be acted upon with a pressure of 50 to 900 bar.

7. hydrogen storage according to one of claims 1 to 6, the container contains highly porous metal foam.

A process for storing hydrogen in which a metal alloy capable of forming metal hydrides of general formula I is provided

Me ¹ _x (Al _y H _z ) _n (I) in the

Me ^{1 is} selected from Sc, Ti, Zr ₁ V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, La, Ce, Pr and Nd, or when x> 2, also a mixture may be of several metals, and x is a number from 1 to 3, y is a number from 1 to 2, z is a number from 4 to 7 and n is a number from 1 to 7, is pressurized in a pressure vessel under pressure with hydrogen.

9. A process for the release of Wassestoff, in which a metal hydride of the general formula I.

Me ¹ _x (Al _y H _z ) _n (I) in the

Me ¹ is selected, Cu of Sc, Ti, Zr, V, Cr, Mn ₁ Fe Co, Ni, Zn, Y, Nb, Mo, La, Ce, Pr and Nd, or when x> 2, also a mixture may be of several metals, and x is a number from 1 to 3, y is a number from 1 to 2, z is a number from 4 to 7 and n is a number from 1 to 7, is kept under hydrogen pressure in a pressure vessel, and Release of the hydrogen takes place by reducing the pressure.