Is A Metal Hydride Hydrogen Storage Sustainable?

Ein Bild, das Diagramm enthält. Automatisch generierte Beschreibung
size of a metal hydride cylinder in comparison with hydrogen steel containers

Metal hydride hydrogen storage cylinders can hold much more hydrogen than other hydrogen storage possibilities like high pressure steel cylinders. The metal hydride canisters for hydrogen are small in size and portable, thus perfect for mobile applications.

We are so exited to have the first price for a market ready metal hydride hydrogen storage. But the prices for hydrogen storage solutions are only one part of the equation.

Durability, contaminants, recyclability and of course the energy density are important factors for metal hydride hydrogen storages.

The first metal hydride storage cylinder manufacturer answered our questions.

They offer for example a hydrogen cartridge with the equivalent of 3000 liters of hydrogen stored in a bottle only 2 feet long with a diameter of 15 cm.

What Metals are used in metal hydride hydrogen batteries?

The experts answer was:

AB2 proprietary powders

The manufacturer won’t tell you his recipe for metal hydride hydrogen storage, but from the literature we know:

“The most important hydrides for the storage of hydrogen are the metallic hydrides. Elemental metals (e.g. palladium, magnesium, lanthanum), intermetallic compounds and light metals (e.g. aluminum) as well as certain alloys (e.g. TiNi-Ti2Ni, Mg-Mg2Ni) are able to store hydrogen.”

(e.g. ZrMn2, LaNi5, Mg2Ni, LiB)

The price of 1kg Titanium is only 110 Dollars. Other than Palladium which is traded for more than 50 Dollars a gram.

hydrogen stored in solids
h2 gas is absorbed at a certain pressure and temperature in metals

What is the Charge and discharge temperature of the metal hydride hydrogen storage?

This is highly depending on the combination of metal hydride. This particular hydrogen component manufacturer says that:

they can work in ambient conditions

Limits: 10°C charging or higher / 65°C discharging or lower

You can heat the metal hydride storage to accelerate charging. When you discharge metal hydride hydrogen containers you will get heat. To accelerate the discharge speed, you can cool the hydrogen container.

What are the losses between charge and discharge?

We all know you loose energy while charging a battery, but do we loos hydrogen while filling and draining the hydrogen cylinders? The hydrogen hydride storage manufacturer says:

no major losses if properly cooled / warmed when absorbed / desorbed. Say roughly a 15% if not properly cooled / warmed as all metal hydrides are thermally dependant

What is the time for charging?

it depends on model and flow provided
So this manufacturer doesn’t give us any useful answer about the time it takes to charge a metal hydride h2 vessel. I can only guess that it is a rather slow process which will be done over night.

What is the charging pressure for metal hydride bottles?

This low pressure, which is needed to fill a metal hydride battery is perfect for all types of high-quality electrolysers. Electrolysers produce mostly between 30 and 40 bar pressurised hydrogen. That mean a metal hydride bottle can be filled directly by the electrolyzer and no hydrogen compressor is necessary.

Sadly, the manufacturer didn’t provide answers to the hydrogen flow rate while discharging the metal hydrides gas cylinders. If you know flow rates, please write in the comments down below.

Is there any contamination of the hydrogen through the storage?

no, H2 released by Metal hydride cartridges is even purified once desorbed
That means at the same time contaminant stay in the hydrogen cartridge.

What happens with water accumulation in the cylinder when temperature drops?

no water accumulation as compatible dry gas supplied
It is good that the Volks-Electrolyzer has such a sophisticated hydrogen drying system.

How can metal hydride cartridges be regulated?

pressure regulator kit additionally supplied and thermal control system

What is the discharge pressure of a metal hydride canister?

depends on pressure reached during refills and on temperature conditions on metal hydride canister

Is the discharge of metal hydride canisters linear?

No, the discharge of hydrogen from a hydride storage is not linear.
That leads to a decrease in power at the hydrogen application.

Is there any degradation?

negligible if used H2 ultrapure and dry gas (proper dew point)

How many cycles do you estimate for the best hydrogen storage solution in metal hydrides?

> 2000 with proper H2 gas purity
The lifetime of a hydrogen storage tank decides its economical value.

Let’s say we can fill the 3000 l metal hydride hydrogen tank 2000 times with 80 kWh and we pay 8.400 € for it, the value of one kilowatt hour of hydrogen will be 5 cents per kilowatt hour (5 cents/kilowatt hour). This is just a way to compare energy storages. Like a lithium battery for 800 Dollars per kWh with 5000 cycles will make 16 cents per kilowatt hours (Lithium 16 c/kWh).

What is the thread on the bottleneck or the metal hydride bottle valve?

various quick connectors or threads on request

not store hydrogen in a carbotainer
the disposal of carbon fiber is expensive. often they will be disposed illegally and pollute the environment

Conclusion: Are metal hydrides economically suggestable and sustainable?

In comparison with fiber composite hydrogen storage solutions, hydrides are nice.

The recycling should be feasible and worth it.
A real downside are the cycles. Metal hydrides are best for mobile applications or transporting purposes. You would have to replace the hydride cartridge every 6 years if you use it really often which will be a great expense. The second downside is the price of hydrogen bound in solid metals.

fuel cell price
price for hydrogen electrolyzers, fuel cells, hydrogen heaters, hydrogen cars and hydrogen equipment like hydrogen tanks and cylinders, Preis Wasserstoffgenerator, Wasserstoff BHKW, Preis Brennstoffzelle, Preis Elektrolyseur, Preis Wasserstofftankstelle

You can compare the price of metal hydride storage solutions with many different hydrogen storages in the international hydrogen pricelist in the members area. It takes seconds to register.

Here you will find some basic information about metal hydride out of the book

Hydrogen in Automotive Engineering Production, Storage, Application

written by Manfred Klell , Helmut Eichlseder · Alexander Trattner

Released in 2017.

Hybrid Storage

5.5 Storage in Physical and Chemical Compounds

Many substances have the property of forming physical or chemical compounds with hydrogen. The bonds can occur in solid, liquid or gaseous media. The main evaluation criteria for the suitability of a compound as hydrogen storage are:

  • Quantity of hydrogen stored per unit of weight and volume
  • Conditions for loading and unloading the storage (temperature, pressure, kinetics)
  • Number of possible loading cycles (lifetime).

Despite sometimes theoretically very high gravimetric and volumetric storage densities, most bonded storage forms are still at the experimental and laboratory stage. In the case of solid-state storage systems in hydrides available on the market, the storage weight is around 30 kg to 40 kg per kg of stored hydrogen, which corresponds to a gravimetric storage density of approx. 3 mass percent hydrogen. In most cases, the conditions for loading and unloading prove to be complex. In any case, storage in compounds has a high potential and is the subject of intensive research. Some general principles should be pointed out here; details can be found in the literature.

5.5.1 Physical and Chemical Adsorption

Depending on pressure and temperature, hydrogen adsorbs physically in molecular form (physisorption) or chemically in atomic form (chemisorption) on solid surfaces. In physisorption, binding occurs through interactions without structural change of the hydrogen molecule. The binding energy is significantly lower in physical adsorption. The material should have a large surface area (pores) to maximize the storage area. The physical adsorption of hydrogen on carbon has been studied in detail. Carbon atoms can form fullerenes, which are multiple pentagonal and hexagonal carbon rings that form a grid. These grids can be rolled up into cylindrical tubes, called nanotubes. Hydrogen is stored by physical adsorption on the surface of these grids, usually at low temperatures of 50 K to 80 K. After initial very high expectations, storage densities of 3–5 weight percent hydrogen have been achieved so far [159]. Since the rapid release of the bound hydrogen also poses problems, no nanostorage devices are yet on the market. Recent research suggests that certain plastics (polyaniline, polypyrrole) can store up to 8 weight percent hydrogen. Combinations of physical and chemical processes are also being investigated.

metallic hydrides

…The most important hydrides for the storage of hydrogen are the metallic hydrides. Elemental metals (e.g. palladium, magnesium, lanthanum), intermetallic compounds and light metals (e.g. aluminum) as well as certain alloys (e.g. TiNi-Ti2Ni, Mg-Mg2Ni) are able to store hydrogen. Hydrogen atoms are chemically incorporated into the metal grid. Researchers are particularly interested in intermetallic compounds consisting of an element with high hydrogen affinity and an element with low hydrogen affinity (e.g. ZrMn2, LaNi5, Mg2Ni, LiB) [387].

Loading and Unloading of Metallic Hydrides

When the hydrogen meets the metal, the hydrogen molecule is first bound to the surface and dissociated into its atoms (dissolution α phase). The hydrogen atoms then diffuse into the material and are incorporated into the metal lattice until they form the hydride β phase, see Fig. 5.19 left. Thermodynamically, the process is represented by isotherms in a pressure-concentration diagram, see Fig. 5.19 right. In the α phase, the hydrogen pressure increases sharply with the concentration [H] (H atom per metal atom) until at [H] ¼ 0.1–0.2the hydrogen passes into the hydride phase. During the period of coexistence of the two phases, hydrogen is incorporated into the metal grid at approximately constant values for temperature and pressure. The width of the horizontal plateau is a measure of how much

hydrogen stored in solids
h2 gas is absorbed at a certain pressure and temperature in metals

Fig. 5.19 Formation and transition phases of metal hydrides. (Source: Schlapbach [308])

hydrogen can be reversibly stored in the hydride. Once hydride formation is complete, the hydrogen pressure increases sharply with further increase in concentration. The plateau width depends on the temperature. Above the critical temperature Tc, a plateau no longer forms.

Loading and unloading takes place at pressures between 1 bar and 60 bar. If a plateau equilibrium exists at temperatures around 20 C to 90 C, one speaks of low-temperature hydrides, at temperatures from 200 C to 300 C of high-temperature hydrides. For most hydrides, the standard enthalpy of formation has a value around ΔFH ¼ 20 MJ per kmol H2. In exothermic absorption, this heat is given off; in endothermic desorption, it must be supplied. Thus, a lot of energy is required for the hydrogen removal process. In reality, the plateau pressure for absorption is somewhat higher than for desorption. This is referred to as hysteresis. If not enough heat is removed during absorption, the rising temperature results in an increased plateau level and the applied hydrogen pressure is no longer sufficient to sustain the reaction.

In terms of safety, hydride storage systems have the advantage that in the event of an accident or leak, the heat supply and the pressure level collapse, resulting in the immediate inactivation of the hydrogen release. Metal hydrides are particularly suitable for supplying fuel cells, as impurities are absorbed at the surface of the metal, releasing hydrogen of high purity.

The disadvantages of hydride storage, apart from the sometimes high cost and weight, are that the storage densities achieved are still low (2–3 mass percent for low-pressure hydrides and 6–8 mass percent for high-pressure hydrides) and that loading and unloading is often not easy to accomplish. The time required for loading and unloading depends on the kinetics of adsorption, dissociation and diffusion. In addition to pressure and temperature, the surface properties of the metal play a major role. On contact with oxygen, an oxide layer forms which can slow down or inhibit chemisorption. Traces of H2S, CO or SO2 also have a similar effect. Often the number of possible cycles is also limited. Loading and unloading usually requires a complex filling station infrastructure.

The hydrogen atoms occupy places in the metal grid and distort it by up to 20% by volume despite their small size. The expansion of the grid occurs anisotropically, i.e. differently in different directions. This leads to structural stresses and, with repeated charging and discharging cycles, to the formation of cracks; the metal disintegrates over time.

Today, hydride storage systems are used in small cartridges for the mobile hydrogen supply of portable small consumers such as laboratory equipment, and occasionally in mobile applications and submarines [64].

1 thought on “Is A Metal Hydride Hydrogen Storage Sustainable?

  1. Armin Benicke says:

    Ich wurde letzten Montag nach einem Energiepodium bei der „Denkfabrik Sachsen“ von einem Zuhörer angesprochen zum Thema der Speicherung von H2. Hier hätte Fraunhofer Dresden eine günstige Lösung mittels Magnesium etc. gefunden. Der Herr wollte mich weiter informieren bzw. Vielleicht gibt es hier Kenner zu genau dem Thema einer Kostengünstigen H2 Lagerung bzw. der folgenden Nutzbarmachung.


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