S. S. Makridis, E. Gkanas, G. Panagakos, E. S. Kikkinides, A. K. Stubos, P. Wagener, S. Barcikowski
Hydrogen is a promising alternative energy carrier that can potentially facilitate the transition from fossil fuels to sources of clean energy because of its prominent advantages such as high energy density (142 MJ per kg), great variety of potential sources (for example water, biomass, organic matter), and low environmental impact (water is the sole combustion product). However, due to its light weight, the efficient storage of hydrogen is still an issue investigated intensely. Various solid media have been considered in that respect among which magnesium hydride stands out as a candidate offering distinct advantages. Recent theoretical work indicates that MgH2 becomes less thermodynamically stable as particle diameter decreases below 2 nm. Our DFT (density functional theory) modeling studies have shown that the smallest enthalpy change, corresponding to 2 unit-cell thickness (1.6 {\AA} Mg/3.0{\AA} MgH2) of the film, is 57.7 kJ/molMg. This enthalpy change is over 10 kJ per molMg smaller than that of the bulk. It is important to note that the range of enthalpy change for systems that are suitable for mobile storage applications is 15 to 24 kJ permolH at 298 K. The important key for the development of air/stable Mg/nanocrystals is the use of PMMA (polymethylmethacrylate) as an encapsulation agent. In our work we use laser ablation, a non-electrochemical method, for producing well dispersed nanoparticles without the presence of any long range aggregation. The observed improved hydrogenation characteristics of the polymer/stable Mg-nanoparticles are associated to the preparation procedure and in any case the polymer laser ablation is a new approach for the production of air/protected and inexpensive Mg/nanoparticles.
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http://arxiv.org/abs/1304.1959
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