H2 Batteries with Magnesium Nanocrystal-Polymer Composites

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In an effort to decarbonize the world’s energy sources, researchers in the field of battery technology have increased focus on the development of Hydrogen batteries as a sustainable solution to the exponentially growing demand for power [1]. Hydrogen batteries, desirable for their fuel source’s abundance (H2 derived from the simple hydrolysis of water), clean emissions after combustion, have four times the energy potential of Lithium polymer batteries when in the form of a metal hydride (Hydrogen ions attached to metal). However, the large tanks necessary to store gaseous or liquid H2 are both impractical and carry significant risk of explosion due to the high pressure. Additionally, the metal components of the battery significantly reduces their storage capacity [2].

Magnesium nanocrystals set into a polymer poly(methyl methacrylate) (PMMA) matrix create a safe, low pressure storage alternative that addresses many of the deficits associated with hydrogen batteries. Magnesium nanoparticles, reacted with gaseous hydrogen to create MgH2 molecules, are significantly lighter than most metal hydrides and can be reused to store additional hydrogen after the initial hydrogen molecules are released to be used in the fuel cell reaction. The PMMA in which the MgH2 molecules are contained is a gas selective matrix which prevents outside oxygen from reacting with the H2, decreasing the battery’s risk of unregulated combustion. The use of nanomaterials in storing gaseous H2 also increases the overall energy density by increasing the volumetric density (ƿ= m/ V), through reducing the value of V by compacting gaseous H2 into the polymer matrix. This allows more energy to be stored per unit of volume or mass [3]. 

Mg Nanocrystals in a gas-barrier polymer matrix.

(Source: Jeon et al., 2011)

References

  1. Bardhan, Rizia, Anne M. Ruminski, Alyssa Brand, and Jeffrey J. Urban. "Magnesium Nanocrystal-polymer Composites: A New Platform for Designer Hydrogen Storage Materials." Energy & Environmental Science 4.12 (2011): 4882. Web.
  2. Jeon, Ki-Joon, Hoi Ri Moon, Anne M. Ruminski, Bin Jiang, Christian Kisielowski, Rizia Bardhan, and Jeffrey J. Urban. "Air-stable Magnesium Nanocomposites Provide Rapid and High-capacity Hydrogen Storage without Using Heavy-metal Catalysts." Nature Materials 10.4 (2011): 286-90. Web.
  3. Atkins, P. W., and Julio De Paula. Elements of Physical Chemistry. Oxford: Oxford UP, 2009. Print.
  4. "Battery Room Hydrogen Detection." H2 Combustible Gas Explosion Risks in Battery Back-up Rooms | Sensidyne. Sensidyne, 2005. Web. 29 Aug. 2015.

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Hydrogen batteries present many benefits in their lack of CO2 emissions and natural abundance. Their use in electric vehicles or cellular communication devices is limited by the large tanks and cryogenic conditions required to store liquid or gaseous hydrogen. By reacting Magnesium nanoparticles with gaseous Hydrogen in a polymer matrix, the Hydrogen can be safely stored as MgH2 molecules at low pressures to be used later to fuel the chemical reactions within the battery. The nanomaterials also decrease the atomic weight of the system which improves storage capacity. Additionally, the selective membrane of the PMMA does not allow for diffusion of O2 into the matrix, improving the safety features of the battery with the decreased risk of combustion [1]. 

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Due to the increased surface area of Mg nanoparticles and additional surface area of nanoparticles in a polymer composite caused by defects (folds or wrinkles in a layer of atoms), H2 atoms exhibit increased thermal and mechanical stability and are more easily forced to run in the forward reaction to produce more products due to a sensitive chemical equilibrium. These enhanced kinetics also contribute to increased association and dissociation of hydrogen, which allows the molecules to more readily form Mg-H2 bonds and just as easily break apart when the hydrogen is required as fuel for the battery. The use of PMMA matrix to coat the nanoparticles is advantageous over traditional ligand coatings in that it is significantly lighter and allows for the selective diffusion of H2 but not O2 [3]. 

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Despite decreased risk of combustion through the use of Magnesium Nanocrystal storage materials, H2 is still explosive in as little as 4% concentrations. Lack of proper ventilation or functional H2 sensors could result in serious fire damage to personnel and equipment in storage facilities. As hydrogen burns with a near invisible pale blue flame, an optical flame detector is also recommended to keep storage facilities safe. H2 batteries for personal electronic devices are not currently feasible due to these safety concerns [4]. 

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