Yunguo Li, Abir De Sarkar, Biswarup Pathak, Rajeev Ahuja
Strain effects on the stabilization of Al dopant atom in graphene oxide (GO) nanosheet as well as its implications for NH3 storage have been investigated using first-principles calculations. The high binding energy of Al ad-atom on GO is found to be a false indicator of its stability. The structural instability clearly contradicts the otherwise high stability indicated by the energetics of Al binding on GO, stressing the need to assess the stability both from energetic and structural perspectives. Tensile strain effectively stabilizes the Al ad-atom on the GO nanosheet by strengthening the C-O bonds through an enhanced electronic charge transfer from C to O atoms. Interestingly, the strength of the C-O bonds is found to be the correct index for Al's stability. The trend for the variation of binding energy with strain is at odds with the systematic analysis of electronic structure based on bond lengths and atomic charges. At an optimal level of strain, the NH3 storage capacity of Al-decorated GO is found to reach its maximum, where each Al ad-atom is able to bind up to 6 NH3 molecules to itself with binding energies in the range of 0.2-1.1 eV. In contrast, the unstrained Al-doped GO is not found to bind even a single NH3 molecule.
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http://arxiv.org/abs/1207.5243
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