cm8b00305_si_001.pdf (1.35 MB)
Anomalous H2 Desorption Rate of NaAlH4 Confined in Nitrogen-Doped Nanoporous Carbon Frameworks
journal contribution
posted on 2018-04-04, 00:00 authored by Christopher
L. Carr, Waruni Jayawardana, Hongyang Zou, James L. White, Farid El Gabaly, Mark S. Conradi, Vitalie Stavila, Mark D. Allendorf, Eric H. MajzoubConfining
NaAlH4 in nanoporous carbon scaffolds is known
to alter the sorption kinetics and/or pathways of the characteristic
bulk hydride reactions through interaction with the framework at the
interface, increased specific surface area of the resulting nanoparticles,
decreased hydrogen diffusion distances, and prevention of phase segregation.
Although the nanosize effects have been well studied, the influence
of the carbon scaffold surface chemistry remains unclear. Here we
compare the hydrogen sorption characteristics of NaAlH4 confined by melt infiltration in nitrogen-doped/undoped ordered
nanoporous carbon of two different geometries. 23Na and 27Al MAS NMR, N2 sorption, and PXRD verify NaAlH4 was successfully confined and remains intact in the carbon
nanopores after infiltration. Both the N-doped/undoped nanoconfined
systems demonstrate improved reversibility in relation to the bulk
hydride during hydrogen desorption/absorption cycling. Isothermal
kinetic measurements indicate a lowering of the activation energy
for H2 desorption by as much as 70 kJ/mol in N-doped frameworks,
far larger than the reduction in carbon-only frameworks. Most interestingly,
this dramatic lowering of the activation energy is accompanied by
an unexpected and anomalously low NaAlH4 desorption rate
in the N-doped frameworks. This suggests that the framework surface
chemistry plays an important role in the desorption process and that
the rate limiting step for desorption may be associated with interactions
of the hydride and host surface. Our results indicate that functionalization
of carbon scaffold surface chemistry with heteroatoms provides a powerful
method of altering the characteristic hydrogen sorption properties
of confined metal hydride systems. This technique may prove beneficial
in the path to a viable metal hydride-based hydrogen storage system.
History
Usage metrics
Categories
Keywords
metal hydride-based hydrogen storage systemhydrogen sorption characteristicsNitrogen-Doped Nanoporous Carbon Frameworks Confining NaAlH 4framework surface chemistrymetal hydride systemsinfiltrationNaAlH 4interactionNaAlH 4 ConfinedN-doped frameworksNaAlH 4 desorption rateAnomalous H 2 Desorption RatePXRDbulk hydride reactionshydrogen diffusion distancescarbon scaffold surface chemistryhydrogen sorption propertiesN 2 sorptionnanoporous carbon scaffoldsH 2 desorption27 Al MAS NMRactivation energy
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC