Hydrogen is considered as a potential candidate for future energy source in automobile industry. Hydrogen storage is the major problem in achieving this goal. In this study, Mg4O-framework with organic linker is replaced with BN linker, borazocine (B4N4H8), and is functionalized with Ti enhancing the stability and storage capacity of the framework. Applying first-principles electronic structure calculations and molecular dynamics simulations the structural stability and hydrogen adsorption capability have been studied on Ti-functionalized Mg-BN-framework (MBF). Ti is functionalized on each BN linker and resulting structure is optimized. Metal atoms bind to BN p ring through Dewar coordination. On saturation with H2 each Ti functionalized B4N4H6 linker traps 4 H2 molecules with 6.0 wt %. First H2 is chemisorbed while remaining H2 molecules are physisorbed. The physisorbed H2 and Ti form Kubas coordination with average   H-H bond length elongated to 0.82 �. H2 adsorption causes Ti atoms to move away from the framework. The average H2 adsorption energy for physisorbed H2 decreases gradually from 0.5 to 0.3 eV. H2 desorption energy is found to be low and decreases from 0.3 to 0.2 eV and hence H2 can be stored reversibly in the Ti functionalized Mg-BN-framework. Molecular dynamics simulations are carried out in canonical NVT ensemble using Nos� thermostat. Simulations are done at 200, 300, 373 and 573 K using G-point sampling with 1 fs time-step for over 5 ps. At 200 K H2 remains bound to Ti in the framework while at 300 K, 75 % H2 desorbed. At 373 K almost all the physisorbed H2 are released including chemisorbed. Clustering effect of Ti atoms is not observed and the framework is found to be structurally stable even at 373 K.  Additional H2 storage in the pore volume increases the wt % from 6.0 to 7.8%.

Hydrogen trapping potential of titanium functionalized Mg-BN-framework

248th National Meeting (2014)

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