Çift katyonlu amin metal bor hidrürlerin hesaplamalı taraması

Many researches are conducted to discover new energy sources. Reasons for this interest can be summarized with the accelerating depletion of conventional fossil fuels, instability of fossil fuel prices due to political reasons, harmful effects on environment and human health. Hydrogen is one of the most promising candidate for future energy source due to its high abundance on earth, high gravimetric energy density and its environment friendly nature. However, absence of a safe and efficient hydrogen storage material is one of the barriers that prevent widespread use of hydrogen as an energy carrier. Even hydrogen can be stored as in the form of gas or liquid, these mediums are not practical in everyday use. As an alternative, hydrogen can also be stored in the solid form. For this purpose, both metal borohydrides and ammines are proposed due to their high gravimetric and volumetric densities. Metal borohydrides have some severe drawbacks e.g. requirement of a very high temperature for the hydrogen decomposition. Therefore, they can be mixed with ammines to form ammine metal borohydrides (AMBs) which have better thermodynamics properties; on the other hand, they lead to undesirable release of harmful by-products. If a second metal is added to ammine metal borohydrides, dual cation AMBs are obtained which have been attracting interest due to their low dehydrogenation temperature, suppressed release of by-product NH3 and high gravimetric hydrogen content. However, only a few of them were synthesized up to now [2–4] and hence there is a lack of information about their crystal structures. In this study, we aim to find the most promising dual cation AMBs with the general formula of M1M2(BH4)x(NH3)y with M1 = Li, Na, K ; M2 = Mg, Ca, Mn, Ni, Sr, Zn; y=2,3,4,5,6 for x = 3 and M1 = Li, Na, K ; M2 = Zr, Ti, Mn, Mo, Co; y=2,3,4,5,6 for x = 5 using computational techniques in particular density functional theory (DFT) which has been successfully used before for similar screening studies [5]. For a DFT calculation, an input including the crystal structure of the considered system must be prepared. Since there is a little information about the crystal structures of dual cation AMBs, it is wise to apply some crystal structure prediction tools to determine their crystal structures. Here, we employed CrystAl Structure Prediction via Simulated Annealing (CASPESA) algorithm [6–11] to reveal the crystal structures of the systems mentioned above. Even these systems have a very complex alloying and decomposition routes, in our screening we assumed a few simple alloying and decomposition reactions to evaluate the complexes following the study of Hummelshøj et al. [5]. [2] Sun, W.W., Chen, X.W., Gu, Q.F., Wallwork, K.S., Tan, Y.B., Tang, Z.W. and Yu, X.B., 2012. A New Ammine Dual-Cation (Li, Mg) Borohydride: Synthesis, Structure, and Dehydrogenation Enhancement, Chem-Eur J, 18(22), 6825–6834. [3] Xia, G.L., Gu, Q.F., Guo, Y.H. and Yu, X.B., 2012. Ammine bimetallic (Na, Zn) borohydride for advanced chemical hydrogen storage, J Mater Chem, 22(15), 7300–7307. [4] Guo, Y.H., Wu, H., Zhou, W. and Yu, X.B., 2011. Dehydrogenation Tuning of Ammine Borohydrides Using Double-Metal Cations, Journal of the American Chemical Society, 133(13), 4690–4693. 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