Micrometer-sized particles encased in tailored polymer membranes
Hereon team unravels how metal hydrides can better store hydrogen

Date:
February 9, 2022
Source:
Helmholtz-Zentrum Hereon
Summary:
Metal hydrides are considered a cutting-edge storage material
for hydrogen. These hydrides function even better, if the
micrometer-sized hydride particles are coated with a thin polymer
film. Using a sophisticated microscopy technique, a team can
now successfully show in detail, how the polymer-coated particles
transform during charging and discharging with hydrogen. The results
are encouraging and bring practical use of the new technology one
step closer.



FULL STORY ========================================================================== Hydrogen is considered a vital component of the energy transition:
it can be produced from solar or wind power and therefore stores green
energy in form of an environmentally friendly energy carrier, providing
energy also at night and during periods of calm winds. Hydrogen also
acts as a climate-neutral fuel for fuel-cell cars and trucks, enabling
greater ranges than battery-powered vehicles. Common pressure gas tanks
for hydrogen vehicles, however, are still too bulky and their cylindrical
shape is difficult to accomodate. The experts are therefore working on an alternative: metal hydride storage. The metal compounds ground into fine powders can bind the hydrogen in astounding quantities. A metal hydride
storage unit can store up to 50% more hydrogen than a 700-bar pressure
tank of the same size, and due to low pressures, is conformable in shape.


========================================================================== Helmholtz-Zentrum Hereon has developed and patented an especially
efficient metal hydride system. "Here we combine several hydrides
together," says Thomas Klassen, director of the Hereon Institute of
Hydrogen Technology and professor at Helmut Schmidt University in
Hamburg. "These hydrides react with each other providing additional
energy for discharge of hydrogen." This reduces the required temperature
for discharge, and the system becomes more energy efficient.

Protection Against Oxygen There are two limitations here, however. On
the one hand, the different hydride components should not separate too
far from each other during hydrogen charging, because their reaction
during discharge would then be too sluggish.

On the other hand, metal hydride particles are susceptible to surface oxidation, blocking hydrogen access. "Both problems can be alleviated by coating the grains with a polymer," says Volker Abetz, director of the
Hereon Institute of Membrane Research and professor at the University
of Hamburg.

"This polymer only allows hydrogen to pass through, but not oxygen,
and it prevents long-range separation of the different metal hydrides."
This polymer trick has actually been known in the laboratory for some
time now.

What exactly was going on, however, had so far been unclear. Through sophisticated imaging, the Abetz and Klassen teams could now visualize the changes during charging and discharging. Initially, the experts produced extremely fine and thinly layered metal hydride samples. They then
examined these samples with a special scanning electron microscope. This resulted in high-resolution images of the micrometer-sized metal hydride
grains coated by the polymer, both in the charged and discharged states.

Excellent Job "Because the method is element specific, the different metal hydrides can be distinguished from one another," explains Abetz. The measurements demonstrate that the polymer coating serves as excellent protection against oxygen.

"Furthermore, we also could observe that the encapsulation in polymers
actually prevents coarsening and segregation of the different metal
hydride components," adds Klassen. "Over many cycles, the system can
quickly be charged and discharged with hydrogen. The polymers are
therefore doing an excellent job!" Based on these new insights, the
Hereon experts are now able to systematically optimize the polymer-coated
metal hydrides. Future plans include searching for further improved and tailored polymers that can be used to coat the hydride particulates even
more effectively. In the framework of a subsequent project together with partners from the Technical University of Hamburg and the University of
Hamburg as well as a commercial company, the researchers wish to test
the concept of polymer coating for stationary hydrogen storage systems,
thereby considerably increasing their durability.

========================================================================== Story Source: Materials provided by Helmholtz-Zentrum_Hereon. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Clarissa Abetz, Prokopios Georgopanos, Claudio Pistidda, Thomas
Klassen,
Volker Abetz. Reactive Hydride Composite Confined in a Polymer
Matrix: New Insights into the Desorption and Absorption of Hydrogen
in a Storage Material with High Cycling Stability. Advanced
Materials Technologies, 2022; 2101584 DOI: 10.1002/admt.202101584 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220209112113.htm

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