Enhancement of polypyrrole electrochemical performance with graphene quantum dots in polypyrrole nanoparticle/graphene quantum dot composites

The influence of graphene quantum dots (GQDs) on the physicochemical properties of polypyrrole nanoparticles (PpyNPs) was investigated experimentally and theoretically. The synthesis of the non-covalent PpyNPs/ GQDs material was based on the known procedure of chemical pyrrole polymerization in the presence of a strong oxidant (ammonium persulfate, APS) and a surfactant (decyltrimethylammonium bromide, DeTAB). The obtained hybrids were in the form of spherical polymeric particles coated with GQDs with a diameter depending on the polymerization time and the amount of GQDs added during the synthesis. The morphology and porosity of the obtained materials were also influenced by the polymerization conditions, namely, composites with a higher GQD content showed higher BET specific surface area. On the other hand, the greatest attention was paid to the study of electrode processes taking place on the electrode modified with the PpyNPs/GQDs composite compared to the modification with pristine PpyNPs. GQDs incorporated into the polymeric network significantly change the energy level distribution at the interphase between Ppy and GQDs. Electronic interaction between both components results in GQDs participation in the Ppy-involved charge transfer processes. In consequence, oxidation of the mixed PpyNPs/GQDs system is much easier compared to the polymer itself. The charge transfer processes involving PpyNPs/GQDs composites are also much faster than those involving electroactive films formed only from PpyNPs. Additionally, a significant increase in the double-layer capacitance current is observed for composite materials. In conclusion, a clear improvement in the electrochemical behavior of polypyrrole in the composite material was observed, which was undoubtedly the result of the introduction of GQDs.