Hydrolysis

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POWERPASTE is an ultra-high capacity hydrogen storage substance for PEM fuel cell applications invented and developed by Fraunhofer IFAM.

POWERPASTE releases hydrogen on contact with water. It has a hydrogen capacity of about 10 mass-% (i.e. 10 kg POWERPASTE → 1 kg hydrogen). This is a specific energy of 1.6 kWhel/kg and an energy density of 1.9 kWh/liter, or about 10 times the capacity of Li-Ion batteries.

The award-winning POWERPASTE technology is patent-pending and offers many advantages over other energy storage technologies, in particular in the power range from 100 W to 10 kW.

Single-use energy storage devices with energy densities of more than 1 kWh/kg and 1 kWh/liter are of interest for various applications. Such storage devices can be realized by means of metal hydrides, which can be hydrolyzed with any kind of naturally occurring water (i.e. tap water or surface water) to generate gaseous hydrogen. One characteristic feature of the hydrolysis reaction is that the protons in the water yield half of the generated hydrogen which effectively doubles the material-specific hydrogen density. Hydrogen produced through hydrolysis can then be converted to electricity by means of fuel cells.  

Thus, compact, safe, long-life and reasonably priced energy sources similar to single-use high-performance batteries can be built – but with many times the energy density of even Li-SOCl₂ batteries. If water is available, ultra-high material-specific gravimetric energy densities of more than 2.3 kWh / kg can be realized – including conversion losses of the fuel cell. This corresponds to a hydrogen storage capacity of 15 wt.%.

Applications

    Backup- and emergency power
    Standalone radiocommunication
    Portable electronic devices and chargers
    Portable stand-by power devices
    Camping and outdoor equipment
    Energy supplies for environmentally sensitive areas
    Sensors and probes
    Beacons, alarm systems, light signals

Advantages of MgH₂ as a hydrolysis agent

 

Fraunhofer IFAM Dresden succeeded in enabling the hydrolysis of highly energetic, non-toxic but also only very inactive MgH₂ in a particularly advantageous way. Not only are the abovementioned energy densities achieved in practice, but also known disadvantages of other hydrolysis materials could be overcome (such disadvantages include a slow reaction speed, expensive noble metal catalysts or nanocrystalline materials, high production costs and material toxicity imposing both limitations to a practical application and the requirement to contain, return and reprocess any spent hydrolysis fuel).

The most important advantages of hydrolyzing MgH₂ according to the Fraunhofer IFAM invention are:

    Very high gravimetric and volumetric energy densities close to the theoretical maximum
    Abundance of the starting materials (i.e. Mg)
    Cost per kWh in the same region as for conventional single-use batteries even today
    High optimization potential for a large-scale production
    Easy material handling (even in air)
    Very long shelf life, no self-discharge
    The hydrolysis reaction can be directly performed with liquid water (no heat or steam necessary)
    Reaction kinetics can be adapted to application-specific needs
    High reaction and system safety
    Noiseless and zero emission energy conversion
    Non-toxicity of both the hydrolysis fuel and the hydrolysis products

Various suitable metal hydride-based hydrolysis fuels and their production are patent pending by Fraunhofer IFAM Dresden, the invention was awarded with the 2013 f-cell award (1st place, category “science”).

Background information

Chemically, the reaction of magnesium hydride with water can be understood by the following equation:

MgH₂ + 2 H₂O  →  2 H₂ + Mg(OH)₂

Commercial MgH2 however reacts with water by generating a Mg(OH)₂ passivation layer on its surface which makes the material unsuitable for hydrolysis without additional measures.

At Fraunhofer IFAM, certain inexpensive, noble metal-free additives were developed. Catalytic amounts of these additives are sufficient to increase the reaction speed by several orders of magnitude which enables a nearly complete hydrolysis reaction of MgH₂ with water within minutes. The underlying reaction mechanism was clarified and it could be shown that the hydrolysis of magnesium hydride can be performed in practice in a controlled, reproducible and efficient way.