Hydrogen Desorption Properties of Lithium–Carbon–Hydrogen System

Abstract

Hydrogen desorption properties of a mixture of hydrogenated nanostructural graphite C nano H x and lithium hydride LiH are demonstrated in this paper, where C nano H x was synthesized from graphite by ballmilling under 1 MPa hydrogen for 80 h. First of all, we clarified the hydrogenated properties of C nano H x synthesized under four different milling conditions. The hydrogen desorption profile with typical two-peak structure was caused by iron contamination in C nano H x from steel balls during ballmilling, while the products prepared by zirconia balls showed the broad single peak in hydrogen desorption. The amount of desorbed hydrocarbon gas from the products using a rocking (vibrating) mill estimated by the thermogravimetry was larger than that using a rotating (planetary) one. Next, the destabilization properties of extremely stable LiH was examined, indicating that LiH was destabilized by mixing with another component LiOH or NaOH, and then, the mixture easily released hydrogen gas at lower temperature compared with LiH, LiOH and NaOH themselves. On the analogy of this result, we examined hydrogen desorption properties of the ballmilled mixture of LiH and C nano H x . The hydrogen desorption started from about 200 C and showed a peak at 350 C, although each product needs more than 400 C to release hydrogen. Since this hydrogen storage system is specially based on lithium, carbon and hydrogen in the mixture, it can be regarded as Li-C-H hydrogen storage system.

Microscopic characterization of metal-carbon-hydrogen composites (metal = Li, Mg)

“…So, Li-C-H system has recently been reported as a way to solute these problems. 23,24 Li-C-H system was synthesized from LiH and nano-structural graphite by ball-milling under hydrogen atmosphere, and it can reversibly absorb and desorb 5 mass% of hydrogen at 350 C under 3.0 MPa H 2 gas atmosphere. Moreover, not only Li-C-H system but also Mg-C-H system has been reported as the superior hydrogen storage material than C nano H x itself.…”

Hydrogen storage properties in a composite of lithium hydride and boron nitride with hydrocarbon groups

“…Therefore, it is suggested that hydrogen atoms or hydrocarbon groups dissociated from CH 4 during the mechanical milling are chemisorbed as the polarized N H, C H and B H groups at the edges of layers in the nano-structured hBN. On the basis of above results, these polarized groups in BN nano CH x should be destabilized by mixing with LiH just like hydrogen desorbing reaction of the C nano H x and LiH composite [10,11]. Fig.…”

“…In a recent study, the C nano H x material was mixed with each alkali (-earth) metal hydride by ball-milling, yielding composite materials (metal-C-H materials) [10][11][12][13]. The metal-C-H material composed of C nano H x and LiH released hydrogen around 350 • C within few hours.…”

“…The metal-C-H material composed of C nano H x and LiH released hydrogen around 350 • C within few hours. Additionally, the hydrocarbon desorption from the C nano H x -LiH composite was strongly suppressed compared with that from the C nano H x material itself [11]. It was considered that the polarized groups such as -CH, -CH 2 or -CH 3 at the edges of graphene in the C nano H x and the ionic crystal of LiH are destabilized by interacting with each other, leading to release of hydrogen gas at lower temperature compared with that of each component [14].…”

Hydrogen desorption properties of Li–BN–H system synthesized by mechanical milling

“…The point is that LiH could react with NH 3 as an ultrafast speed to release H 2 at lower temperature comparing with the decomposition temperature of LiH or NH 3 themselves. On the basis of the point of view, Ichikawa et al designed a new type of hydrogen storage material, metal-C-H system [8,9], which can store more than 4.5 wt% H 2 reversibly around 350 1C.…”