Abstract
To improve the hydrogen storage properties of Mg/MgH2, a Ni and TiO2 co-doped reduced graphene oxide [(Ni-TiO2)@rGO] nanocomposite is synthesized by a facile impregnation method and introduced into Mg via ball milling. The results demonstrated that the dispersive distribution of Ni and TiO2 with a particle size of 20–200 nm in the reduced graphene oxide matrix led to superior catalytic effects on the hydrogen storage properties of Mg-(Ni-TiO2)@rGO. The initial hydrogenation/dehydrogenation temperature for Mg-(Ni-TiO2)@rGO decreased to 323/479 K, 75/84 K lower than that of the additive-free sample. The hydrogen desorption capacity of the Mg-(Ni-TiO2)@rGO composite released 1.47 wt.% within 120 min at 498 K. When the temperature was increased to 523 K, the hydrogen desorption capacity increased to 4.30 wt.% within 30 min. A hydrogenation/dehydrogenation apparent activation energy of 47.0/99.3 kJ·mol−1 was obtained for the Mg-(Ni-TiO2)@rGO composite. The improvement in hydrogenation and dehydrogenation for the Mg-(Ni-TiO2)@rGO composite was due to the reduction of the apparent activation energy by the catalytic action of (Ni-TiO2)@rGO.
Highlights
Hydrogen is a highly promising clean energy source
It can be observed that Ti, O and Ni elements are well-scattered on the surface of the reduced graphene oxide sheets
A lattice spacing of 0.178 nm matching with the (200) plane of Ni could be detected in Figure 4e, further indicating that the (Ni-TiO2)@rGO nanocomposite had been successfully fabricated via a facile impregnation method
Summary
Hydrogen storage materials represent one of the key technologies for the development of hydrogen energy. Magnesium is considered to be the most promising hydrogen storage material because of its high theoretical hydrogen storage capacity (7.6 wt.%), abundant reserves and low cost (Jain et al, 2010; Liu et al, 2015). Its practical application is limited due to its thermodynamic stability and poor kinetic performance. To overcome these weaknesses, methods such as alloying (Oh et al, 2016; Hardian et al, 2018; Li et al, 2018), nanocrystallization (Wagemans et al, 2005; Li et al, 2007) and the addition of catalysts has been employed (Cui et al, 2014; Huang et al, 2017; Zhang et al, 2017; Wang et al, 2019; Yang et al, 2019) Methods such as alloying (Oh et al, 2016; Hardian et al, 2018; Li et al, 2018), nanocrystallization (Wagemans et al, 2005; Li et al, 2007) and the addition of catalysts has been employed (Cui et al, 2014; Huang et al, 2017; Zhang et al, 2017; Wang et al, 2019; Yang et al, 2019).
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