Studies into the Storage of Hydrogen in Carbon Nanofibers: Proposal of a Possible Reaction Mechanism

Abstract

Substantial levels of hydrogen, up to 6.5 wt %, have been stored in carbon nanofibers (CNFs) under conditions of 12 MPa pressure and ambient temperature. The magnitude of this result cannot be interpreted in terms of physisorption on the external surface alone. Kinetic studies indicate that a slow chemisorption process is involved. The rate of uptake corresponds to that of hydrogen dissociation on graphite edge sites. Such a finding proposes a novel mechanism, offering a plausible explanation for these unusually high experimental observations. This involves the initial dissociation of hydrogen, believed to be catalyzed by carbon edge sites, which constitute the majority of the nanofiber surface, a property which is probably an important contributory factor toward their high hydrogen storage capacities.

Hydrogen spillover to enhance hydrogen storage—study of the effect of carbon physicochemical properties

“…Oxygen functional groups have also been shown to play a role in physisorption of hydrogen on activated carbon: increasing oxidation of an activated carbon resulted in increased physisorption [12]. Graphitic carbon may be capable of dissociating hydrogen [13]; in fact, several groups have asserted that carbon nanotubes and nanofibers are capable of hydrogen dissociation and that this hydrogen in turn is able to intercalate the interlayer spacing of graphite nanofibers [14]. The effect of surface functionalities on hydrogen spillover to carbon has not been widely stud-ied, but hydrogen spillover has been shown to chemically modify functional groups on carbon to form basic carbons [15].…”

Development of Doped Nanoporous Carbons for Hydrogen Storage

“…Use of a Sievert's apparatus with a differential pressure transducer was reported to give reproducible hydrogen uptakes of +/-0.1% for 100 mg of sorbent. 15 In our case, use of 100 mg sample is calculated to give 0.2% error, based on both sample replicates and propagation of error.…”

The hydrogen storage capacity of metal-containing polyacrylonitrile-based electrospun carbon nanofibers

“…Panella et al [27] reported that the hydrogen storage capacities of carbon materials are proportional to their micropore volumes. However, it has previously been reported [28,29] that specific surface areas and micropore volumes are not necessarily the primary markers for greater hydrogen storage capacity. In addition, it is possible that the investigated metals play intermedimicropores and mesopores.…”