Li-Functionalized Carbon Nanotubes for Hydrogen Storage: Importance of Size Effects
2019 (engelsk)Inngår i: ACS APPLIED NANO MATERIALS, ISSN 2574-0970, Vol. 2, nr 5, s. 3021-3030Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]
We investigated Li-doped carbon nanotubes (CNTs) as a promising hydrogen storage media. In this computational model, we considered isolated lithium atom adsorbed on a CNT wall as an adsorption site for hydrogen. We focused on the influence of size effects on the structural and energetic characteristics of CNT(n,n)@Li+kH(2) complexes where n = 5, 7, 9; k = 1,..., 6; N, = 4, 5, 6 (N-c is translation length of CNT, expressed in terms of a number of CNT unit cells). We proved that modeled CNT length substantially influences internal sorption of Li and hydrogen on the narrow tube (5,5), which subsequently alters the adsorption energies of H-2 molecules and causes the deformation of the carbon framework. Moreover, the size effects are not pronounced in the case of external sorption for all considered CNT translation lengths and diameters. We have not observed any noticeable qualitative difference between internal and external hydrogen sorption in the nanotube wider than CNT(5,5). In the case of external adsorption on all considered nanotubes, doping with Li increases hydrogen adsorption energies of up to four H-2 molecules by 100 meV in comparison with pure CNTs. And the local density approximation estimations (similar to 250 meV/H-2) of adsorption energy on Li-decorated CNTs exceed the lowest requirement proposed by the U.S. Department of Energy (200 meV/H-2). In the case of internal sorption on Li-functionalized tubes, the generalized gradient approximation also gives hydrogen adsorption energies in the desired range of 200-600 meV/H-2. However, steric hindrances could prevent sufficient hydrogen uptakes (less than 2 wt % inside CNT(5,5)). We believe that our findings on the size effects are important for estimation of CNT's hydrogen storage properties.
sted, utgiver, år, opplag, sider
AMER CHEMICAL SOC , 2019. Vol. 2, nr 5, s. 3021-3030
Emneord [en]
carbon nanotubes, hydrogen adsorption, Li-functionalization, DFT, periodic boundary condition
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-254030DOI: 10.1021/acsanm.9b00406ISI: 000469410000049Scopus ID: 2-s2.0-85078379965OAI: oai:DiVA.org:kth-254030DiVA, id: diva2:1342833
Merknad
QC 20190814
2019-08-142019-08-142022-06-26bibliografisk kontrollert