Improving the Electrochemical Performance and Stability of Polypyrrole by Polymerizing Ionic Liquids

Abstract

Polypyrrole (PPy) based electroactive materials are important building blocks for the development of flexible electronics, bio-sensors and actuator devices. As the properties and behavior of PPy depends strongly on the operating environment—electrolyte, solvent, etc., it is desirable to plant immobile ionic species into PPy films to ensure stable response. A premade ionic polymer is not optimal in many cases, as it enforces its own structure on the conducting polymer, therefore, polymerization during fabrication is preferred. Pyrrole (Py) was electropolymerized at low temperature together with a polymerizable ionic liquid (PIL) monomer in a one-step polymerization, to form a stable film on the working electrode. The structure and morphology of the PPyPIL films were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FTIR) spectroscopy and solid-state NMR (ssNMR) spectroscopy. The spectroscopy results confirmed the successful polymerization of Py to PPy and PIL monomer to PIL. The presence of (TFSI–) anions that balance the charge in PPyPIL was confirmed by EDX analysis. The electrical properties of PPyPIL in lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) aqueous and propylene carbonate solutions were examined with cyclic voltammetry (CV), chronoamperometry, and chronopotentiometry. The blend of PPyPIL had mixed electronic/ionic conductive properties that were strongly influenced by the solvent. In aqueous electrolyte, the electrical conductivity was 30 times lower and the diffusion coefficient 1.5 times higher than in the organic electrolyte. Importantly, the capacity, current density, and charge density were found to stay consistent, independent of the choice of solvent.

Polypyrrole with Phosphor Tungsten Acid and Carbide-Derived Carbon: Change of Solvent in Electropolymerization and Linear Actuation

“…PPyCDC revealed the best specific capacitance in this research with similar values found for CDC particles spray coated on a PVdF membrane [ 55 ] in the range of 31–39 F g −1 applied in the same solvent PC. Recent research [ 56 ] using electropolymerized PPy in combination with polymerized ionic liquids (PIL) forming PPyPIL films led to specific capacitance either in aqueous or organic electrolyte in the range of 75 F g −1 .…”

Electrochemically Produced Copolymers of Pyrrole and Its Derivatives: A Plentitude of Material Properties Using “Simple” Heterocyclic Co-Monomers

“…Electroctropolymerisation of Py and an ionic liquid monomer was carried out in order to obtain PPy with improved electrochemical properties [ 19 ]. The detailed analysis of products indicates that a blend of homopolymers was formed rather than a copolymer.…”

“…Taking into account the complex nature of electrochemical polymerisation and significant influence of the employed process conditions, different copolymer structures can be expected in the case of different pyrrole co-monomers, as shown in Scheme 2 . Based on the complex electropolymerisation mechanism, random [ 18 ] and block copolymers, graft copolymers, interpenetrating polymer blends [ 19 ], as well as complex systems of different products can be expected. This is reflected in the published works on pyrrole copolymers obtained not only by electrochemical, but also by chemical oxidative copolymerisation, in which copolymers with complex architectures were formed [ 20 ].…”

Solvent Effect in Imidazole-Based Poly(Ionic liquid) Membranes: Energy Storage and Sensing

“…The PIL monomer synthesis is shown in the Supplementary Information, with the reaction given in Scheme S1 with the 1 HNMR signals shown in Figure S1, as has been reported in previous research [20]. The PIL monomer was poured into a Teflon mold and polymerized at 60 • C using an initiator (AIBN), with a reaction time of 36 h. The obtained PIL film was 80 ± 2 µm thick and was washed several times with ethanol to remove residual unreacted monomer and dried in an oven at 40 • C (2 mbar) for 24 h.…”

“…This showed a specific capacitance of 12 F g −1 [46] while the protic PIL polymers from 1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide, with few percentages of water, up to 3.8% [47], led to a specific capacitance in the range of 18 to 20 F g −1 , which showed that the addition of water reduced the electrochemical stability window. In most cases, PILs applied with the addition of deposited polypyrrole in the solid state showed a pseudo capacitance in the range of 5 F g −1 [48], while direct polymerization of pyrrole with PIL monomers reached 74 F g −1 [20]. Due to the differences in capacitance and electrochemical stability in the case of different electrolyte solvents, the sensor properties of the PIL films was investigated.…”