Understanding the Protonation of Polyaniline and Polyaniline-Graphene Interaction

The stability and electronic structure of (protonated) polyaniline (PANT) and PANI-graphene composite are systematically studied using density-functional simulations. The protonation of PANI is a spontaneous exothermic reaction. It decreases the band gap of PANI and introduces shallow impurity states (ISs), both of which tend to increase the conductivity of PANT at finite temperatures. The binding between PANT and graphene is dominated by strong van der Waals interaction and modified by the charge-transfer dipolar attraction, the latter of which leads to the increase of the PANI-graphene binding by protonation. The interaction from graphene upshifts the shallow ISs, even into the band gap of PANI. This not only can considerably ease the electronic excitation in finite temperatures but also explains the experimentally concluded site selectivity of the PANI-carbon nanotube interaction. The charge transfer between PANI and graphene is dependent on the protonation degree and temperature. This work explains many experimental observations and is helpful for further investigation and application of PANI and PANI-graphene and PANI-carbon nanotube composites.