Abstract
NiCo nanoalloy (4–6 nm) encapsulated in grapheme layers (NiCo@G) has been prepared by thermolysis of a 3D bimetallic complex CoCo[Ni(EDTA)]2·4H2O and successfully employed as a catalyst to improve the dehydrogenation performances of LiAlH4 by solid ball-milling. NiCo@G presents a superior catalytic effect on the dehydrogenation of LiAlH4. For LiAlH4 doped with 1 wt% NiCo@G (LiAlH4-1 wt% NiCo@G), the onset dehydrogenation temperature of LiAlH4 is as low as 43 °C, which is 109 °C lower than that of pristine LiAlH4. 7.3 wt% of hydrogen can be released from LiAlH4-1 wt% NiCo@G at 150 °C within 60 min. The activation energies of LiAlH4 dehydrogenation are extremely reduced by 1 wt% NiCo@G doping.
Highlights
NiCo nanoalloy (4–6 nm) encapsulated in grapheme layers (NiCo@G) has been prepared by thermolysis of a 3D bimetallic complex CoCo[Ni(EDTA)]2·4H2O and successfully employed as a catalyst to improve the dehydrogenation performances of LiAlH4 by solid ball-milling
In the last two decades, LiAlH4 has received particular attention aiming at reducing the operation temperature to meet the DOE criteria because it can release a total amount of 7.9 wt% of hydrogen in two steps below a relatively low temperature, e.g. 220 °C
Different methods have been explored for decrease of the dehydrogenation temperature of LiAlH4, including particle size reduction by ball milling[11], synthesis of multi-hydride composites[12], and doping with catalysts[13,14]
Summary
5.9 wt% and 3.7 wt% of hydrogen are respectively released for LiAlH4-5 wt% NiCo@G and LiAlH4-10 wt% NiCo@G, due to the increasing catalyst percent and the premature dehydrogenation during the ball milling process. Total 7.3 wt% of hydrogen can be thoroughly released within 60 min for LiAlH4-1 wt% NiCo@G while 350 min for as-milled LiAlH4 This result confirms that dehydrogenation kinetics are significantly improved by addition of NiCo@G. Decreases after doping with 1 wt% NiCo@G, leading to more grain boundaries and larger surface area This important observation suggests that NiCo@G readily influences the LiAlH4 texture at room temperature during the ball milling process, by preliminarily breaking their particle aggregation. A more in depth study of the effect of NiCo@G on LiAlH4 dehydrogenation, in particular regarding the critical roles of Ni/Co and catalyst/LiAlH4 ratios, is in process
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