LiBH 4 @Carbon Micro-Macrocellular Foams: Tuning Hydrogen Release through Varying Microporosity
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LiBH4@Carbon Micro-Macrocellular Foams: Tuning Hydrogen Release through Varying Microporosity
Nicolas Brun,1 Raphaël Janot,2 Chrystel Gervais,3 Clément Sanchez3 and Rénal Backov1 1
Centre de Recherche Paul Pascal, UPR 8641-CNRS, Université de Bordeaux, 115 Avenue
Albert Schweitzer, 33600 Pessac, France. 2
Laboratoire de Réactivité et Chimie des Solides, UMR 6007 CNRS, Université de Picardie
Jules Verne, 33 Rue Saint Leu, 80039 Amiens, France. 3
Laboratoire de Chimie de la Matière Condensée de Paris, UMR 7574 CNRS, UPMC,
Université Paris 06, Collège de France, 11 Place Marcelin Berthelot, 75231 Paris, France. ABSTRACT Microporous-macroporous carbononaceous monolith-type materials, prepared through a hard template method using silica as exo-templating matrices, have been impregnated by an etheric solution of LiBH4 to prepare LiBH4@Carbon samples. It has been shown that the amorphous character of LiBH4 is largely favoured when developing the carbon microporosity (pores smaller than 2 nm) and that LiBH4 dehydrogenation is strongly enhanced at low temperatures. The onset temperature of dehydrogenation can be decreased to 200°C and hydrogen capacity reaching 4.0 wt.% is obtained at 300°C with the carbon having the largest microporous volume, whereas the hydrogen release for bulk LiBH4 is negligible at the same temperature. In addition to some irreversible reactions with carbon surface groups the explanation for such modification could lie in the LiBH4 destabilization through confinement to the nanoscale range and associated amorphization. INTRODUCTION Borohydrides have recently attracted much attention due to both their high hydrogen contents and their associated use for hydrogen storage [1], features particularly true for LiBH4 when considering its very high hydrogen content (18.4 wt%) and good volumetric capacity (121 kg.m-3 H2). The complete recovery of the whole hydrogen content of LiBH4 remains however difficult as the dehydrogenation of LiH, formed as an intermediate decomposition product, occurs at rather high temperatures (above 600°C) thereby limiting the hydrogen release to 13.8 wt.% [1]. In order to address Li(BH4) decomposition it is useful to promote their heterogeneous nucleation within carbonaceous mesocellular materials [2]. In the present study, these microporous-macroporous carbonaceous monolith-type materials, prepared through a hard template method, have been impregnated by an etheric solution of LiBH4 to prepare LiBH4@Carbon-HIPE samples, where the hydrogen release temperature is controlled upon varying the Carbon-HIPE monoliths microporosity.
EXPERIMENTAL DETAILS Synthesis of porous carbon monoliths. The whole detailed synthetic pathways can be found elsewhere[3]. Basically, a monolith of silica-HIPE (0.5 g) was added into a 25 wt.% or 80 wt.% Ablaphene® RS101 solution in THF. For a good impregnation, the suspension was placed under vacuum until the effervescence disappeared. After 24 hours aging at room temperature, the solution was filtered. The monolith was then quickly washed with THF an
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