Higher hydrogen uptake capacity of C2H4Ti+ than C2H4Ti: a quantum chemical study

Using density functionals theory, we show that gravimetric hydrogen uptake of C2H4Ti complex and its cation, C2H4Ti+, differ by about 2 wt%. Six and five hydrogen molecules are found to be adsorbed on C2H4Ti+ and C2H4Ti complexes thereby showing a hydrogen-uptake capacity of 13.74 and 11.72 wt%, respectively. All hydrogen molecules are adsorbed in molecular form on C2H4Ti+ ion with an increase in metal bond strength, whereas in some cases, the hydrogen molecules are found to be dissociated on C2H4Ti neutral complex. The uptake capacity of neutral C2H4Ti complex shown in this work is in excellent agreement with that reported experimentally, Phillips and Shivaram (Phys Rev Lett 100:105505, 2008). The H-2 adsorption energy and its dependence on exchange and correlation functions in density functionals method were illustrated. Even after the adsorption of maximum number of hydrogen molecules on C2H4Ti and C2H4Ti+ complexes, Ti and Ti+ remain strongly bound to C2H4 substrate.