Carbon Allotropes Grafted with Poly (pyrrole) Derivatives Via Living Radical Polymerizations: Electrochemical Analysis of Nano-Composites for Energy Storage

Abstract

In this study two living radical polymerization techniques, e-ATRP and RAFT, were applied for the grafting carbon allotropes such as MWCNT, Graphene and SWCNH with the methacrylate functionalized-poly(pyrrole). The modified carbons were examined as the polymerization initiators in the e-ATRP and RAFT synthesis. Their electrochemical response for the co-catalyst activity revealed the highest activation rate constant for SWCNH, owing to its highest specific surface area, and thus availability of large electrochemical interface for the redox process. The Fourier-transform infrared and Raman spectroscopies were used to identify the reaction products at each phase and for the final composites. TEM imaging showed that: (i) the morphology of composites made from the same carbon allotrope are not significantly different for RAFT and e-ATRP products; (ii) the structure of the ultimate product strongly depends on the type of carbon: for SWCNH the polymer was locally agglomerated between the carbon clusters due to ultra-small carbon particles, and for the Graphene, the polymer formed an uniform layer on the most outer sheets of Graphene; (iii) the poly(pyrrole) film or the particle size was very small (in all cases less than 30 nm), demonstrating the control over the polymer morphology in living polymerization techniques. The high specific gravimetric capacitances over 456 F g-1 and electrochemical stability up to 7500 cycles were obtained for MWCNT-grafted-poly(pyrrole), and slightly less for Graphene-based composites synthetized by e-ATRP, showing the advantages of this method over RAFT. The electrode voltages for all composites were higher as compared to the pure polymer electrodes, with some benefit of RAFT over e-ATRP product, and with significant improvement observed for the MWCNT- and Graphene-based systems. Regardless of the synthesis method, all composites demonstrated enhanced specific capacitance as compared to their individual components, revealing the synergy of double-layer capacitance from the carbon and the pseudo-capacitance generated by the polymer fraction. Both, the RAFT and e-ATRP are polymerization methods that deliver nanomaterials with tailored morphology and desired functions, by creating a stable anchorage between carbon, molecular linker and the polymer, and without unwanted side effects such as the homopolymerization, as indicated in our previous studies on similar carbon/poly(pyrrole systems. Figure 1