In this study, the electrospinning performance and solution properties of Nafion and its blend with another polyelectrolyte, poly(acrylic acid) (PAA), were investigated. Attempts to electrospin pure ...Nafion at various polymer concentrations (5−35 wt %), solvents, neutralization, and electrospinning conditions resulted in electrospraying rather than electrospinning. However, a polymer solution blend (5 wt %) of Nafion and PAA resulted in beaded fibers at 8 wt % PAA and smooth electrospinning above 12% PAA. Fiber sizes of the blend increased from 90 to 600 nm with increasing PAA content. Dynamic light scattering on pure Nafion solutions in various solvents reveals large aggregates (i.e., dispersion) of various sizes due to polymer backbone and ionic interactions. The lack of sufficient polymer chain entanglement evidenced by low viscosity and aggregate formation in Nafion solutions prohibits fiber formation during electrospinning. The addition of PAA to Nafion modifies the ionic strength of the solvent resulting in suppressed aggregate formation, increased viscosity, and subsequently enhanced polymer chain entanglement. Coincidentally, the onset of suppressed aggregate formation in the blend solution coincides with the electrospraying−electrospinning transition (8% PAA). In addition, thermal treatment enhances water stability of the electrospun blend fibers.
A polymerized ionic liquid diblock copolymer (PILBCP-TFSI), poly(MMA-b-MUBIm-TFSI), consisting of an ionic liquid monomer, (1-(2-methacryloyloxy)undecyl-3-butylimidazolium ...bis(trifluoromethane)sulfonamide) (MUBIm-TFSI), and a non-ionic monomer, methyl methacrylate (MMA), was synthesized via reverse addition fragmentation chain transfer polymerization followed by anion exchange metathesis. Free standing, mechanically stable transparent solid polymer films were produced with PILBCP-TFSI containing 1 M lithium bis(trifluoromethane)sulfonamide in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Li-TFSI/EMIm-TFSI). The resulting PILBCP-TFSI + Li-TFSI/EMIm-TFSI films possessed ion conductivities from 1 to 10 mS cm−1 from 25 °C to 105 °C. Solid-state lithium-ion coin cell batteries were assembled and tested at room temperature with PILBCP-TFSI + Li-TFSI/EMIm-TFSI films as the solid-state electrolyte and separator and resulted in a maximum discharge capacity of 112 mAh g−1 at 0.1 C with a Coulombic efficiency greater than 94% over 100 cycles. For the first time, these results demonstrate the feasibility of PIL block copolymers as solid-state electrolytes and separators in lithium-ion batteries.
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•Polymerized ionic liquid (PIL) diblock copolymer synthesized for batteries.•High ionic conductivity of >1 mS cm−1 at 25 °C.•PIL diblock copolymer as solid-state electrolyte and separator in Li-ion battery.•Li-ion battery max discharge performance of 112 mAh g−1 at 25 °C.•Coulombic efficiency greater than 94% for 100 cycles at 25 °C.
Herein, we report a polymerized ionic liquid diblock copolymer with high hydroxide conductivity and nanoscale morphology. Surprisingly, the conductivity is not only higher (over an order of ...magnitude) than its random copolymer analog at the same ion and water content, but also higher than its homopolymer analog, which has a higher ion and water content than the block copolymer. These results should have a significant impact on low-cost (platinum-free), long-lasting, solid-state alkaline fuel cells.
Ionic conductivity in new polymerized ionic liquids is of great interest as it applies to solid-state electrolytes for electrochemical and electromechanical applications. In this study, an ionic ...liquid monomer was synthesized and polymerized into random copolymers and their ionic conductivity and structure were investigated as a function of copolymer composition. Both nonionic−ionic and ionic−ionic copolymers were synthesized, where the nonionic and ionic monomers were hexyl methacrylate (HMA) and a methacrylate-based imidizolium neutralized with tetrafluoroborate (BF4) or bis(trifluoromethane sulfonyl)imide (TFSI). In the nonionic−ionic copolymer, the ionic conductivity increased by over an order of magnitude with increasing HMA composition, even though the overall charge content decreased, because the addition of HMA significantly lowered the glass transition temperature. The ionic conductivity also increased by more than an order of magnitude in the ionic−ionic copolymer with increasing TFSI content, even though there was no change in the overall charge content, because substituting the larger anion TFSI for BF4 resulted in weaker ionic interactions and also significantly lowered the glass transition temperature. In both types of copolymers, the temperature dependence of the ionic conductivity was well described by both Arrhenius and Vogel−Tamman−Fulcher models. An important difference between the two classes of random copolymers was that the nonionic−ionic copolymer exhibited microphase separation in X-ray scattering that correlated with a discontinuity in the increasing ionic conductivity with increasing HMA content suggesting that structure can also play a significant role in ion transport in polymerized ionic liquids.
Hybrid-capacitors have the potential to synergistically combine the benefits of both electrochemical double layer capacitors (EDLCs) (long cycle life) and Faradaic-capacitors (high capacitance). ...However, new processes that intimately combine the two primary materials from each capacitor (carbon and conductive polymer, respectively) within the electrodes in an ordered fashion on the nanoscale are needed to realize this potential. In this study, we report on a novel method (simultaneous electrospinning/electrospraying (E/E)) for fabricating hybrid-capacitors with high surface area electrodes consisting of polyaniline (PANI) and carbon nanoparticles (referred to as E/E electrodes). E/E produces a unique nanofiber/particle network of PANI and carbon. The hybrid-capacitor with E/E electrodes exhibits an excellent specific capacitance of 235Fg−1 (vs. 138 Fg−1 for capacitor with state-of-the art hybrid electrodes) at a current density of 1Ag−1. Moreover, the hybrid-capacitor with E/E electrodes retains approximately 84% capacitance after 1000 charge-discharge cycles (vs. 67% for capacitor with state-of-the art hybrid electrodes). These results indicate the feasibility of producing E/E electrodes and their promise as future materials in hybrid-capacitors.
Chemical bath deposition (CBD) is an inexpensive and reproducible method for depositing ZnO nanowire arrays over large areas. The aqueous Zn(NO3)2−hexamethylenetetramine (HMTA) chemistry is one of ...the most common CBD chemistries for ZnO nanowire synthesis, but some details of the reaction mechanism are still not well-understood. Here, we report the use of in situ attenuated total reflection Fourier transform infrared (ATR−FTIR) spectroscopy to study HMTA adsorption from aqueous solutions onto ZnO nanoparticle films and show that HMTA does not adsorb on ZnO. This result refutes earlier claims that the anisotropic morphology arises from HMTA adsorbing onto and capping the ZnO {10 1̅ 0} faces. We conclude that the role of HMTA in the CBD of ZnO nanowires is only to control the saturation index of ZnO. Furthermore, we demonstrate the first deposition of ZnO nanowire arrays at 90 °C and near-neutral pH conditions without HMTA. Nanowires were grown using the pH buffer 2-(N-morpholino)ethanesulfonic acid (MES) and continuous titratation with KOH to maintain the same pH conditions where growth with HMTA occurs. This semi-batch synthetic method opens many new opportunities to tailor the ZnO morphology and properties by independently controlling temperature and pH.
A polymerized ionic liquid (PIL) diblock copolymer with a long alkyl side-chain, poly(MMA-b-MUBIm-Br), was synthesized at various compositions from an ionic liquid monomer, ...(1-(2-methacryloyloxy)undecyl-3-butylimidazolium bromide) (MUBIm-Br), and a non-ionic monomer, methyl methacrylate (MMA). The PIL diblock copolymer was synthesized via post-functionalization from its non-ionic precursor PIL diblock copolymer, poly(MMA-b-BrUMA) (BrUMA = 11-bromoundecyl methacrylate), which was synthesized via the reverse addition fragmentation chain transfer (RAFT) polymerization technique. Differential scanning calorimetry reveals two distinct constant glass transition temperatures (Tgs) with a low PIL segment Tg. These PIL block copolymers result in easily processable, flexible, transparent films with high mechanical strength. A high bromide ion conductivity of 64.85 mS cm−1 at 80 °C and 90% RH was measured for the PIL diblock copolymer with an ion exchange capacity (IEC) of 1.44 meq/g (23.3 mol% MUBIm-Br). Interestingly, this result was three times higher than its analogous PIL homopolymer (2.75 meq/g; 100 mol% MUBIm-Br) and an order of magnitude higher than a PIL block copolymer from a previous study with similar chemistry, similar IEC, higher water content, but shorter alkyl side-chain length. Ion conductivity did not scale as expected with water content, which is unusual for water-assisted ion transport (e.g., protons, hydroxide, chloride) in ion-containing polymers, and therefore suggests other mechanisms that impact ion transport in PIL block copolymers.
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The effect of morphology on ion transport in ionic liquid-based solid-state films was investigated. In this study, mixtures of a block copolymer, poly(styrene-b-methyl methacrylate) (SbMMA), and an ...ionic liquid (IL), 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide (EMIm-TFSI), were prepared as clear solid-state films at various IL compositions (0–50 wt%) by solution casting from a volatile co-solvent. The IL was preferentially miscible with the MMA block as evidenced by visual inspection and differential scanning calorimetry. Both equilibrium and non-equilibrium morphologies were identified with X-ray scattering and transmission electron microscopy and the morphology varied with MMA/IL volume fraction. The morphology and microdomain orientation had a significant impact on ionic conductivity. Higher through-plane conductivities were observed in morphologies with a three-dimensionally continuous conducting path (e.g., non-conducting S cylinders) compared to morphologies with a non-continuous conducting path (e.g., lamellae). When the lamellae were oriented in the plane, the through-plane conductivity was significantly lower than the in-plane conductivity, while the conductivity was direction-independent when the morphologies have a continuous conductive path. Also, a significant increase in conductivity was observed with increasing IL content at the glass transition of the conductive (MMA/IL) microdomain. Finally, significantly higher ionic conductivities can be achieved in a block copolymer/IL solid-state film compared to a homopolymer/IL film at the same IL content (wt%), because the non-conductive microdomain excludes IL, which produces a higher local IL concentration in the conductive phase.
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