Catalytic effects of nano-sized TiC additions on the hydrogen storage properties of LiAlH4

The catalytic effect of TiC nanopowder addition in varying proportions on the hydrogen storage properties of LiAlH4 has been investigated by pressure-composition-temperature (PCT) experiments, thermogravimetry (TG), and differential scanning calorimetry (DSC). The results indicate that doped samples are able to dehydrogenate at much lower temperatures; for example, the onset of dehydrogenation is 85 °C for LiAlH4–2 mol% TiC, and the majority of hydrogen (∼6.9 wt.%) can be released by 188 °C. About 5 out of 6.9 wt.% of H2 can be released in the range of 85–138 °C (heating rate 4 °C min−1). Isothermal desorption results at 115 °C reveal that doped alanate exhibits dehydriding rate 7–8 times faster than that of pure LiAlH4. DSC measurements indicate that enthalpies of decomposition in LiAlH4 decrease significantly with doping. From Kissinger analysis, the apparent activation energies are estimated to be 59 kJ/mol, 70 kJ/mol and 99 kJ/mol for the decompositions of LiAlH4, Li3AlH6 and LiH, respectively. The results of first rehydrogenation indicate that 5 mol% dopant exhibits the maximum absorption of about 1.9 wt.%. XRD, FESEM, EDS, FTIR, and XPS analyses are utilized to put forward a possible catalytic mechanism of nano-sized TiC in ameliorating the dehydriding/rehydriding characteristics of doped LiAlH4.

Research highlights▶ For the first time, the effects of nano-sized TiC doping on the hydrogen storage characteristics of Li alanate have been investigated. ▶ The nano-sized TiC-doped Li alanate is shown to have greater and improved hydrogen performance in terms of minimum loss in hydrogen release capacity, kinetics, and initial temperature of decomposition, over the undoped Li alanate. ▶ Investigations reveal that the apparent activation energy as well as the enthalpy of dehydrogenation is considerably lowered by the addition of TiC nanopowder. ▶ Isothermal desorption results at 115 °C reveal that doped alanate exhibits dehydriding rate 7–8 times faster than that of pure LiAlH4. ▶ Out of the various samples corresponding to LiAlH4–x mol% TiC (x = 1, 2, 3, 4 and 5), the sample with x = 2 mol% presents the optimum material. ▶ It shows highest desorption rate leading to about 6.9 wt.% of H2 by 188 °C (heating rate 4 °C min−1). ▶ LiAlH4 doped with 5 mol% doping exhibits the maximum rehydrogenation capacity of 1.9 wt.% of hydrogen at 165 °C and 9.5 MPa. ▶ XRD, FESEM–EDS, FTIR, and XPS analyses show that nano TiC particles act as surface catalyst and remain stable during the milling process. ▶ Various kinetic models have been examined for the isothermal dehydrogenation of the doped samples.