H2 storage and equilibrium isotope effect for Be, Li, and Ti-doped closoborate complexes

Abstract

This work reports hydrogen uptake capacity and equilibrium isotope effect (EIE) for the Be, Li, and Ti-doped closoborate (B6H6) complexes using first-principles calculations at MP2/6-311++G** level. The EIE was obtained using vibrational frequencies of H2 and D2-adsorbed B6H6M (M = Be, Li, and Ti) complexes at MP2/6-311++G** level. Two, three, and four H2/D2 molecules get adsorbed on B6H6Be, B6H6Li, and B6H6Ti respectively. The gravimetric H2(D2) uptake capacity of B6H6Be, B6H6Li, and B6H6Ti complexes is found to be 4.8(9.5), 7.2(13.44), and 6.3(11.94) wt% respectively. H2 adsorption is thermodynamically favorable on B6H6Ti at ambient conditions, whereas it is unfavorable on B6H6Li and B6H6Be complexes. Contribution from each vibrational mode in calculating the equilibrium isotope effect is obtained. The EIE calculated using vibrational frequencies for the B6H6Be(1H2/1D2), B6H6Be(2H2/2D2), B6H6Li(1H2/1D2), B6H6Li(2H2/2D2), B6H6Li(3H2/3D2), B6H6Ti(2H2/2D2), B6H6Ti(3H2/3D2), and B6H6Ti(4H2/4D2) complexes is found to be 0.56, 0.26, 0.76, 0.93, 1.05, 0.25, 0.05, and 0.75 respectively. In case of B6H6Ti(1H2) complex, the hydrogen is adsorbed in atomic form. It is found that D2 binds better than the H2 to the B6H6M (M = Be, Li, and Ti) complex.