Inclusion of CoTiO_(3) to ameliorate the re/dehydrogenation properties of the Mg–Na–Al system

For the first time,the MgH_(2)–NaAlH_(4)(ratio 4:1)destabilized system with CoTiO_(3) addition has been explored.The CoTiO_(3)-doped MgH_(2)–NaAlH_(4) sample begins to dehydrogenate at 130℃,which is declined by 40℃ compared to the undoped MgH_(2)–NaAlH_(4).Moreover,the de/rehydrogenation kinetics characteristics of the CoTiO_(3)-doped MgH_(2)–NaAlH_(4) were greatly ameliorated.With the inclusion of CoTiO_(3),the MgH_(2)–NaAlH_(4) composite absorbed 5.2 wt.%H_(2),higher than undoped MgH_(2)–NaAlH_(4).In the context of dehydrogenation,the CoTiO_(3)-doped MgH_(2)–NaAlH_(4) sample desorbed 2.6 wt.%H_(2),almost doubled compared to the amount of hydrogen desorbed from the undoped MgH_(2)–NaAlH_(4) sample.The activation energy obtained by the Kissinger analysis for MgH_(2) decomposition was significantly lower by 35.9 kJ/mol than the undoped MgH_(2)–NaAlH_(4) sample.The reaction mechanism demonstrated that new phases of MgCo and AlTi_(3) were generated in situ during the heating process and are likely to play a substantial catalytic function and be useful in ameliorating the de/rehydrogenation properties of the destabilized MgH_(2)–NaAlH_(4) system with the inclusion of CoTiO_(3).

A balance between catalysis and nanoconfinement towards enhanced hydrogen storage performance of NaAlH_(4)

Owing to its favorable thermodynamics and high density,NaAlH_(4) has been widely regarded as a potential hydrogen storage material,but its practical application is hindered by the sluggish kinetics,high operating temperature and poor cycling stability.Here,taking advantage of Co-doped nanoporous carbon scaffolds as structural host,we develop a new strategy to balance the synergistic effect between the catalytic role of Co nanoparticles and the nanoconfinement role of porous carbon scaffolds via the controllable etching of Co nanoparticles towards enhanced hydrogen storage performance of NaAlH_(4).The etching of Co nanoparticles creates extra void spaces nearby catalytically active Co nanoparticles,which not only exerts the catalytic effect of Co nanoparticles,but also improves the nanoconfinement role in maintaining the cycling stability towards increased loading ratio and hence high systematic capacity.Induced by this balanced synergistic effect,the peak temperature for the dehydrogenation of NaAlH_(4) could be reduced to 164°C,97°C lower than the bulk counterpart,even under an ultrahigh loading ratio of 67%,and more importantly,the reversible systematic hydrogen storage capacity could still reach 3.3 wt.%after 5 cycles.This work opens up a new avenue to improve the hydrogen storage performance of various complex hydrides.