Mechanistic Aspects of the Functionalization of Graphene Oxide with Ethylene Diamine: Implications for Energy Storage Applications

Diamine functionalization of GO continues to draw significant research attention because of the ability to manipulate the interlayer spacing between GO sheets. Control over the GO interlayer spacing has resulted in profound improvements in the capacitance and cyclic stability in lithium-ion batteries. The reaction of ethylene diamine (EDA) with GO has previously been reported to cause simultaneous "stitching/crosslinking", "reduction", and "functionalization"of GO. However, detailed understanding of "stitching"and "reduction"is still lacking. In the present work, we have used combinatorial experimental and computational approaches to determine the reactivity of EDA toward main oxygen-containing functional groups of GO (epoxy, hydroxyl, and carboxylic acid). Using excess EDA, we observed experimental predominant evidence of "stitching", which was further corroborated with DFT calculations. However, no clear experimental evidence of "reduction"of GO as a result of reaction of EDA with GO was observed. DFT calculations revealed that the first step of EDA functionalization exhibits similar reaction energies for hydroxyl and epoxy groups. However, in regard to "stitching", hydroxyl and carboxyl groups were energetically comparable. The present results have implications in regard to energy storage applications of these materials.