Hydrogen sorption efficiency of titanium-functionalized Mg-BN framework

Abstract

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, metal-organic framework (MOF) with organic linker is replaced with BN linker namely borazocine (B4N4H 8) and is functionalized with Ti, enhancing the stability and storage capacity of the framework. A first-principles electronic structure calculation using spin polarized generalized gradient approximation with Perdew-Burke-Ernzerhof functional, structural optimization and molecular dynamics (MD) simulations have been performed for hydrogen sorption efficiency of the Ti-functionalized Mg4O-BN framework (MBF). Low adsorption and desorption energies suggest the high hydrogen reversibility of the system. BN ring coordinates strongly with the Ti metal by Dewar interaction while each Ti metal adsorbs 4 H2 molecules by Kubas interaction. In MD simulations, 75% of the physisorbed H2 molecules are desorbed at 300 K while at 373 K chemisorbed hydrogen also began to desorb with the MBF framework remaining structurally stable. The average hydrogen desorption temperature using van't Hoff equation is predicted to be 323 K with hydrogen storage capacity of 7.8 wt %. For the first time, the H2 sorption efficiency of the Ti-functionalized metal-BN framework has been studied and is found to be better than MOF or metal-functionalized MOF with respect to storage capacity, stability, and reversibility, making it a potential hydrogen storage material.