Conductivity and interaction mechanism of polydopamine-graphene oxide: A combined experimental and density functional theory investigation

Abstract

Abstract The electrochemical activity of electrode material plays an important role in enhancing energy storage efficiency in flow batteries (FBs). Polydopamine (PDA) mixed with graphene oxide (GO) exhibited improved performance. However, few studies investigated on the interplay between DA and GO, particularly the influence of GO's functional groups on its adsorption efficacy. In this study, the prepared PDA-GO composites were formed by a straightforward and eco-friendly approach. The impact of the PDA on GO's electrical conductivity and the ratio of the DA-to-GO was explored. Furthermore, the impacts of various oxygen-containing functional groups on the adsorption DA process of GO were thoroughly explored using density functional theory (DFT) calculations. Focusing on the adsorption energy, charge density difference, energy gap, and reaction barrier. PDA-GO exhibits the strongest electrical conductivity where the addition ratio of DA-to-GO is 1:2. PDA partially reduction the GO in the process of combining with GO, and the layer spacing increases. DFT calculations indicated that the reduction of DA to GO happens mostly in the epoxy groups, and the basal plane of PDA-GO remains reasonably intact, while the conductivity is greatly improved by the binding of DA to the epoxy groups. DA molecules tend to align parallel to the graphene sheet during the optimization process. The results suggest that a portion of DA molecules infiltrate the interlayer of GO, engaging in π-π and hydrogen bonding interactions with GO during the preparation phase. On the other hand, the epoxy group significantly destroys the π-π interaction between GO and DA, resulting in a reduction in the adsorption energy between the two, whereas the remaining functional groups enhance both. However, the augmentation of the DA adsorption energy by the hydroxyl groups on the surface of the GO is dramatically diminished when the hydroxyl groups on GO reach a particular density owing to the breakdown of the π-π interaction. This study serves as a theoretical foundation for the selective synthesis of PDA-GO composites and fresh ideas for their further utilization in electrode materials.