Quantum chemistry of lithium graphene interactions: catalytic activity of the phenolate

SALGADO, A.; RADOVIC, L.; GARCÍA, X.:
Proceeding The first latino american workshop on carbon materials for energy and the environment, Vol.1 167-168 (2014).

Abstract

Interest in the fundamental aspects of lithium-graphene interactions has grown tremendously over the past several decades, as their applications evolved from intercalation compounds to char and biomass gasification catalysis. Lately, the focus is on carbon-based energy storage in rechargeable batteries, where phenolic surface groups presumably play an important role in improving the capacity of reduced graphene oxide. Here we report the results of our ongoing studies, using density functional theory (DFT), to gain an improved mechanistic understanding of chemisorption, surface rearrangement and desorption pathways for oxygen when an alkali phenolate is present at varying distances from a reactive zigzag site in graphene.

The Gaussian quantum chemistry software is used to study the interaction of O₂ with a free zigzag site in prototypical graphene molecules that have an –OLi group in its vicinity. The DFT model chemistry selected was B3LYP with the 6-31G(d) basis set; special care was exercised in the analysis of the spin multiplicity (M) of both ground and transition states. Transition-state structures were sought using the QST2 and/or QST3 procedures.

Chemisorption is found to be exothermic in all cases and it is barrierless in the presence of lithium phenolate. Surface rearrangement is endothermic in the absence of the phenolate, and becomes exothermic in its presence. Furthermore, the highest barrier, for the cleavage of the bond between adsorbed O atoms, is reduced from ca. 13 to ca. 6.0 kcal/mol, as a consequence of Li-O attraction. Finally, the mechanistic pathway found for oxygen reaction in the presence of lithium phenolate is analogous to the mechanism when alkali phenolate is absent. But, when lithium is present there is a path that leads to desorption of CO, rather than CO₂, in remarkable analogy to what has been suggested to proceed in the absence of alkali phenolates.