Ionic Block Copolymers Research Articles

Ionic nanoporous membranes from self-assembled liquid crystalline brush-like imidazolium triblock copolymers.

There is a need to generate mechanically and thermally robust ionic nanoporous membranes for separation and fuel cell applications. Herein, we report a general approach to the preparation of ionic nanoporous membranes through custom synthesis, self-assembly, and subsequent chemical manipulations of ionic brush block copolymers. We synthesized polynorbornene-based triblock copolymers containing imidazolium cations balanced by counter anions in the central block, side-chain liquid crystalline units, and sidechain polylactide end blocks. This unique platform comprises: (1) imidazolium/bis(trifluoromethanesulfonyl)imide (TFSI) as the middle block, which has an excellent ion-exchange ability, (2) cyanobiphenyl liquid crystalline end block, a sterically hindered hydrophobic segment, which is chemically stable and immune to hydroxide attack, (3) polylactide brush-like units on the other end block that is easily etched under mild alkaline conditions and (4) a polynorbornene backbone, a lightly crosslinked system that offers mechanical robustness. These membranes retain their morphology before and after backbone crosslinking as well as etching of polylactide sidechains. The ion exchange performance and dimensional stability of these membranes were investigated by water uptake capability and swelling ratio. Moreover, the length of the carbon spacer in the imidazolium/TFSI central block moiety endowed the membrane with improved ionic conductivity. The ionic nanoporous materials are unusual due to their singular thermal, mechanical, alkaline stability and ion transport properties. Applications of these materials include electrochemical actuators, solid-state ionic nanochannel biosensors, and ion-conducting membranes.

Tailoring surface and bulk morphologies to control transport properties of sulfonated block copolymer films

We examine the effects of solvent composition and solution-casting protocol on the structure of a lamellar sulfonated pentablock copolymer (SPC) membrane. Films are prepared by a layering process, wherein the film is built up through sequential bar-coating steps. Process variables include bar gap height, which controls drying time and layer thickness, and solvent selectivity toward each block in the SPC, which controls solution-state structure and biases the domain orientations at the surface. We find that irrespective of solvent selectivity, one-layer films have poorly ordered structures in the bulk with minimal restructuring near the surface. However, when the process involves sequential deposition of two or more layers, then the bulk structure of dry films can be well-predicted by the solution-state structure, and domain orientations at the surface are templated by polymer-solvent interactions. Consequently, processing conditions strongly influence through-plane transport properties of the SPC films. When the casting process generates disordered lamellae in bulk with a perpendicular lamellar orientation at the surface, both water and protons can move across the film. However, when the process generates highly ordered lamellae in bulk and parallel lamellar orientations at the surface, transport of both water and protons is inhibited by limited pathways. Significantly, the methodology outlined in this work can be extended to other ionic block copolymer platforms, allowing researchers to tailor bulk and surface morphologies for optimization of critical transport properties.

PH-Dependent Solution Micellar Structure of Amphoteric Polypeptoid Block Copolymers with Positionally Controlled Ionizable Sites.

While solution micellization of ionic block copolymers (BCP) with randomly distributed ionization sites along the hydrophilic segments has been extensively studied, the roles of positionally controlled ionization sites along the BCP chains in their micellization and resulting micellar structure remain comparatively less understood. Herein, three amphoteric polypeptoid block copolymers carrying two oppositely charged ionizable sites, with one fixed at the hydrophobic terminus and the other varyingly positioned along the hydrophilic segment, have been synthesized by sequential ring-opening polymerization method. The presence of the ionizable site at the hydrophobic segment terminus is expected to promote polymer association toward equilibrium micellar structures in an aqueous solution. The concurrent presence of oppositely charged ionizable sites on the polymer chains allows the polymer association to be electrostatically modulated in a broad pH range (ca. 2-12). Micellization of the amphoteric polypeptoid BCP in dilute aqueous solution and the resulting micellar structure at different solution pHs was investigated by a combination of scattering and microscopic methods. Negative-stain transmission-electron microscopy (TEM), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS) analyses revealed the dominant presence of core-shell-type spherical micelles and occasional rod-like micelles with liquid crystalline (LC) domains in the micellar core. The micellar structures (e.g., aggregation number, radius of gyration, chain packing in the micelle) were found to be dependent on the solution pH and the position of the ionizable site along the chain. This study has highlighted the potential of controlling the position of ionizable sites along the BCP polymer to modulate the electrostatic and LC interactions, thus tailoring the micellar structure at different solution pH values in water.

Modulating Water Distribution and the Intramicellar Assembly of Sequence-Defined Ionic Peptoid Block Copolymers by the Ionic Monomer Position

Modulating Water Distribution and the Intramicellar Assembly of Sequence-Defined Ionic Peptoid Block Copolymers by the Ionic Monomer Position

Single‐ion conducting polymer as lithium salt additive in polymerized ionic liquid block copolymer electrolyte

AbstractHerein, we describe the use of single‐ion conducting block copolymer (SIC) as an additional lithium salt additive to a ternary solid polymer electrolyte (SPE), consisting of a poly(styrene‐b‐1‐((2‐acryloyloxy)ethyl)‐3‐butylimidazolium bis(trifluoromethanesulfo‐nyl)imide) (S‐ImTFSI64‐16) block copolymer, a N‐propyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) ionic liquid (IL) and a lithium bis(fluorosulfonyl) imide (LiFSI) salt. For this purpose, the S‐ImTFSI64‐16 was substituted by a SIC, based on poly(styrene‐b‐((4‐styrenesulfonyl)(trifluoromethanesulfonyl)imide lithium salt)) (S‐STFSILi64‐16), at various molar ratios. The impact of the SIC concentration on the phase behavior and transport properties of the SPEs was investigated by means of differential scanning calorimetry, electrochemical impedance spectroscopy, and diffusion NMR. In addition, the electrochemical performance of the SPEs was assessed in lithium symmetrical cell at 50 and 80°C. Finally, the cycling performance of a selected SPE was also assessed at 80°C in a Li│NMC111 cell with capacity loading of 1.3 mAh.cm−2 at a C‐rate of 0.1 C. The Li│NMC111 full cell was able to deliver a stable capacity of 0.94 mAh.cm−2 after 20 cycles, corresponding to a capacity of 117 mAh.g−1. These results demonstrates that PIL block copolymer—IL—salt composites represent a promising choice of electrolyte for the next generation of solid‐state high energy density lithium metal batteries.

Cascade Processes with Micellar Reaction Media: Recent Advances and Future Directions.

Reducing the use of solvents is an important aim of green chemistry. Using micelles self-assembled from amphiphilic molecules dispersed in water (considered a green solvent) has facilitated reactions of organic compounds. When performing reactions in micelles, the hydrophobic effect can considerably accelerate apparent reaction rates, as well as enhance selectivity. Here, we review micellar reaction media and their potential role in sustainable chemical production. The focus of this review is applications of engineered amphiphilic systems for reactions (surface-active ionic liquids, designer surfactants, and block copolymers) as reaction media. Micelles are a versatile platform for performing a large array of organic chemistries using water as the bulk solvent. Building on this foundation, synthetic sequences combining several reaction steps in one pot have been developed. Telescoping multiple reactions can reduce solvent waste by limiting the volume of solvents, as well as eliminating purification processes. Thus, in particular, we review recent advances in “one-pot” multistep reactions achieved using micellar reaction media with potential applications in medicinal chemistry and agrochemistry. Photocatalyzed reactions in micellar reaction media are also discussed. In addition to the use of micelles, we emphasize the process (steps to isolate the product and reuse the catalyst).

Unraveling the Role of Charge Patterning in the Micellar Structure of Sequence-Defined Amphiphilic Peptoid Oligomers by Molecular Dynamics Simulations.

Electrostatic interactions play a significant role in regulating biological systems and have received increasing attention due to their usefulness in designing advanced stimulus-responsive materials. Polypeptoids are highly tunable N-substituted peptidomimetic polymers that lack backbone hydrogen bonding and chirality. Therefore, polypeptoids are suitable systems to study the effect of noncovalent interactions of substituents without complications of backbone intramolecular and intermolecular hydrogen bonding. In this study, all-atom molecular dynamics (MD) simulations were performed on micelles formed by a series of sequence-defined ionic polypeptoid block copolymers consisting of a hydrophobic segment and a hydrophilic segment in an aqueous solution. By combining the results from MD simulations and experimental small-angle neutron scattering data, further insights were gained into the internal structure of the formed polypeptoid micelles, which is not always directly accessible from experiments. In addition, information was gained into the physics of the noncovalent interactions responsible for the self-assembly of weakly charged polypeptoids in an aqueous solution. While the aggregation number is governed by electrostatic repulsion of the negatively charged carboxylate (COO–) substituents on the polypeptoid chain within the micelle, MD simulations indicate that the position of the charge on singly charged chains mediates the shape of the micelle through the charge–dipole interactions between the COO– substituent and the surrounding water. Therefore, the polypeptoid micelles formed from the single-charged series offer the possibility for tailorable micelle shapes. In contrast, the polypeptoid micelles formed from the triple-charged series are characterized by more pronounced electrostatic repulsion that competes with more significant charge–sodium interactions, making it difficult to predict the shape of the micelles. This work has helped further develop design principles for the shape and structure of self-assembled micelles by controlling the position of charged moieties on the backbone of polypeptoid block copolymers.

Reversal of handedness of ionic liquid-based chiral block copolymers via self-assembly in solution and bulk phase

Polymerized ionic liquid-based block copolymer obtained by the functionalization of polystyrene-block-poly(4-vinylpyridine) with chiral auxiliaries demonstrated self-assembled helical nanofibrils with inversion of helical sense.

Development and Progression of Polymer Electrolytes for Batteries: Influence of Structure and Chemistry.

Polymer electrolytes continue to offer the opportunity for safer, high-performing next-generation battery technology. The benefits of a polymeric electrolyte system lie in its ease of processing and flexibility, while ion transport and mechanical strength have been highlighted for improvement. This report discusses how factors, specifically the chemistry and structure of the polymers, have driven the progression of these materials from the early days of PEO. The introduction of ionic polymers has led to advances in ionic conductivity while the use of block copolymers has also increased the mechanical properties and provided more flexibility in solid polymer electrolyte development. The combination of these two, ionic block copolymer materials, are still in their early stages but offer exciting possibilities for the future of this field.

Ionic Liquid Composite Electrocatalysts for the Oxygen Reduction Reaction in PEM Fuel Cells

The cathode catalyst layer (CCL) of the proton exchange membrane fuel cell (PEMFC) cathode requires a high amount of Pt to compensate for the sluggish oxygen reduction reaction (ORR) kinetics. Reducing the Pt loading in the CCL remains the major challenge in commercializing fuel cell devices. Recent developments enable up to 20-fold improvement in the activity of ORR electrocatalysts and facilitate a lower amount of Pt in the catalyst layer.1 However, these low-Pt-loaded cathodes show significant voltage losses at high current densities (HCD).2 These performance losses are associated with local oxygen transport resistances due to higher particle-particle distance and the interfacial resistance between Pt and PFSA-based ionomers.3 The interfacial resistance observed at the catalyst-ionomer interface is exacerbated with the thickness of the ionomer film on catalyst particles4 and specific adsorption of sulfonate groups.5 These challenges can be potentially addressed by modifying the catalyst-ionomer interface at fuel cell cathode. Protic and hydrophobic Ionic liquids (ILs) are known to enhance the ORR performance of state-of-the-art catalysts in half cell experiments.6 Our research group has previously shown that an ionic liquid interlayer on the Pt surface mitigates the specific adsorption of sulfonate groups. Despite remarkable half-cell performance of ionic liquid modified catalysts (100-150%), ionic liquid incorporated CCLs show only a modest improvement (10-15%).7 Inhomogeneous distribution of ionic liquids in the catalyst layer and potential loss of ionic liquids during fuel cell operation are possible reasons behind this discrepancy. The use of sulfonated polymerized ionic liquid block copolymer (SPILBCP) as an ionomer presents a novel method to incorporate ionic liquids in the catalyst layer. SPILBCP has sulfonated domains to enable proton conduction and ionic liquid domains to facilitate oxygen transport and mitigate sulfonate adsorption. In this work, we implement rotating disk electrode (RDE) techniques to analyze a polymeric ionic liquid block copolymer (SPILBCP) as an ionomer for the PEMFC cathode. We found that Pt/C catalyst films prepared using PILBCP show two-fold improvement over those prepared using Nafion, a state-of-the-art ionomer. We use the CO displacement technique to show that PILBCP thin films exhibit a lower degree of sulfonate adsorption than Nafion on a highly ordered Pt surface. Furthermore, thin films of SPILBCP and Nafion show comparable proton conductivity and oxygen permeability. These results support the recent finding showing up to two-fold improvement in the kinetic activity of PEMFCs using SPILBCP as a catalyst binder. 8 References Shao M, Chang Q, Dodelet JP, Chenitz R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem Rev. 2016;116(6):3594-3657. doi:10.1021/acs.chemrev.5b00462 Kongkanand A, Mathias MF. The Priority and Challenge of High-Power Performance of Low-Platinum Proton-Exchange Membrane Fuel Cells. J Phys Chem Lett. 2016;7(7):1127-1137. doi:10.1021/acs.jpclett.6b00216 Weber AZ, Kusoglu A. Unexplained transport resistances for low-loaded fuel-cell catalyst layers. J Mater Chem A. 2014;2(41):17207-17211. doi:10.1039/c4ta02952f Sasikumar G, Ihm JW, Ryu H. Dependence of optimum Nafion content in catalyst layer on platinum loading. J Power Sources. 2004;132(1-2):11-17. doi:10.1016/j.jpowsour.2003.12.060 Garrick TR, Moylan TE, Yarlagadda V, Kongkanand A. Characterizing electrolyte and platinum interface in PEM fuel cells using CO displacement. J Electrochem Soc. 2017;164(2):F60-F64. doi:10.1149/2.0551702jes Snyder J, Fujita T, Chen MW, Erlebacher J. Oxygen reduction in nanoporous metal-ionic liquid composite electrocatalysts. Nat Mater. 2010;9(11):904-907. doi:10.1038/nmat2878 Snyder J, Livi K, Erlebacher J. Oxygen reduction reaction performance of [MTBD][beti]-encapsulated nanoporous NiPt alloy nanoparticles. Adv Funct Mater. 2013;23(44):5494-5501. doi:10.1002/adfm.201301144 Li Y, Cleve T Van, Sun R, et al. Modifying the Electrocatalyst-Ionomer Interface via Sulfonated Poly ( Ionic Liquid ) Block Copolymers to Enable High-Performance Polymer Electrolyte Fuel Cells. 2020. Figure 1

(Invited) Linking Ionomer/Electrocatalyst Interactions to Membrane Electrode Assembly Performance and Durability in Proton Exchange Membrane Fuel Cells

The proper integration of materials to enable high performing low temperature fuel cell operation has never been more crucial to realizing the isolated (e.g. half-cell or ex-situ) improvements of advanced electrocatalysts, supports and ionomers in an effort to maximize efficiency. The integration pathway for oxygen reduction electrocatalysts, from initial testing in a rotating disk electrode (RDE) to their apex form as porous electrodes in a membrane electrode assembly (MEA) is replete with potential pitfalls. Along the route to improving MEA level electrocatalyst kinetics and electrode transport properties are numerous choices relating to ink formulation (i.e. solvents and solvent ratios), ink processing and deposition methodology, ionomer content and chemistry and electrochemical MEA conditioning. Combined with carbon morphology/porosity, such variables can alter the final electrode morphology, influencing active site accessibility and ORR activity as well as oxygen transport resistance and electrode proton conductivity.[1–5]Here, the development and utilization of in situ diagnostics designed to probe specific phenomena (e.g. catalyst/ionomer interactions, molecular and Knudsen diffusion, electrochemical active site accessibility and catalyst layer proton resistance) will be presented as tools to contrast the ink, processing and fabrication methods necessary to achieve high performance PGM (e.g. Pt/C and Pt alloy/C) and PGM-free (e.g. FeNx/C) electrocatalysts based electrodes. For PGM based MEAs, the dynamic effects of electrochemical conditioning will be examined in an effort to both baseline MEA level performance and decouple the contributions of simultaneous electrocatalyst particle growth and the removal of system impurities.[6] The prerequisite understanding gleaned from the application of electrochemical diagnostics and MEA conditioning procedures will be combined with the development of a novel sulfonated ionic liquid block copolymer ionomer and tailored integration methodology to illustrate a pathway towards improved MEA level performance.[7] Lastly, alterations in ionomer interactions as a function of accelerated stress tests will be discussed, providing insight into the evolving electrode structure as the community targets more robust systems capable of efficient operation for 25,000 hrs.[8]References[1] A. Orfanidi, P.J. Rheinlander, N. Schulte, H.A. Gasteiger, Ink Solvent Dependence of the Ionomer Distribution in the Catalyst Layer of a PEMFC, Journal of The Electrochemical Society. (2018) 11.[2] S. Khandavalli, J.H. Park, N.N. Kariuki, D.J. Myers, J.J. Stickel, K. Hurst, K.C. Neyerlin, M. Ulsh, S.A. Mauger, Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks, ACS Appl. Mater. Interfaces. (2018) 13.[3] D.A. Cullen, R. Koestner, R.S. Kukreja, Z.Y. Liu, S. Minko, O. Trotsenko, A. Tokarev, L. Guetaz, H.M. Meyer, C.M. Parish, K.L. More, Imaging and Microanalysis of Thin Ionomer Layers by Scanning Transmission Electron Microscopy, J. Electrochem. Soc. 161 (2014) F1111–F1117. https://doi.org/10.1149/2.1091410jes.[4] T. Van Cleve, S. Khandavalli, A. Chowdhury, S. Medina, S. Pylypenko, M. Wang, K.L. More, N. Kariuki, D.J. Myers, A.Z. Weber, S.A. Mauger, M. Ulsh, K.C. Neyerlin, Dictating Pt-Based Electrocatalyst Performance in Polymer Electrolyte Fuel Cells, from Formulation to Application, ACS Appl. Mater. Interfaces. 11 (2019) 46953–46964. https://doi.org/10.1021/acsami.9b17614.[5] G. Wang, L. Osmieri, A.G. Star, J. Pfeilsticker, K.C. Neyerlin, Elucidating the Role of Ionomer in the Performance of Platinum Group Metal-free Catalyst Layer via in situ Electrochemical Diagnostics, J. Electrochem. Soc. 167 (2020) 044519. https://doi.org/10.1149/1945-7111/ab7aa1.[6] S. Kabir, D.J. Myers, N. Kariuki, J. Park, G. Wang, A. Baker, N. Macauley, R. Mukundan, K.L. More, K.C. Neyerlin, Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study, ACS Appl. Mater. Interfaces. 11 (2019) 45016–45030. https://doi.org/10.1021/acsami.9b11365.[7] Y. Li, T.V. Cleve, R. Sun, R. Gawas, G. Wang, M. Tang, Y.A. Elabd, J. Snyder, K.C. Neyerlin, Modifying the Electrocatalyst−Ionomer Interface via Sulfonated Poly(ionic liquid) Block Copolymers to Enable High- Performance Polymer Electrolyte Fuel Cells, ACS Energy Letters. (2020) 6.[8] D.A. Cullen, K.C. Neyerlin, R.K. Ahluwalia, R. Mukundan, K.L. More, R.L. Borup, A.Z. Weber, D.J. Myers, A. Kusoglu, New roads and challenges for fuel cells in heavy-duty transportation, Nature Energy. (2021) 1–13. https://doi.org/10.1038/s41560-021-00775-z.

Ordered isoporous membranes from ionic diblock copolymers via SNIPS: Optimizing effective factors with a structural survey

The membrane formation directly through the self-assembly and nonsolvent induced phase separation (SNIPS) method without the aid of foreign additives has been more challenging in the case of ionic block copolymers, like polystyrene-block-poly (acrylic acid) (PS-b-PAA), in comparison with non-ionic amphiphilic systems. Herein, the influence of governing factors on the structure tuning, including physicochemical characteristics of polymer, solvent and nonsolvent, casting parameters and process conditions to prepare additive-free and ordered isoporous membranes was studied. Due to the high degree of ionization and hydrophilicity of PAA blocks, micellization in the form of “reverse micelles” was aimed to induce more stable micelles assembly. The well-ordered micelles assembly was generated by the suitable selection of solvent (1,4-dioxane), strongly segregated characteristic of PS-b-PAA (high χN) and proper adjustment of casting parameters including polymer concentration and solvent evaporation rate and time. The uniformity and regularity of the micelles assembly during phase inversion step was preserved owing to the high freezing point of solvent. Highly permeable asymmetric isoporous membranes prepared over a wide range of evaporation times (40–120 s) using relatively low polymer concentrations (15 wt%) with adjustable and monodispersed pore-size in the range of sub-10 up to 22 nm. FESEM and AFM images in addition to DLS measurements and solution SAXS analysis were applied to demonstrate the hexagonal close-packed (HCP) structure of micelles assembly and partially hexagonal arrangement of pores at the membrane selective-layer. It was also demonstrated that corona (PS) of adjacent micelles on the membrane surface fused together to form a continuous membrane matrix, while surface-pores were the nanoscale voids, formed between the densely packed spherical reverse micelles practically immobilized by immersion in low-temperature water bath. Such additive-free, asymmetric, iso- and nano-porous membranes have attractive potential practical applications in biomedical and pharmaceutical industries for size-based separations, in addition to their conventional applications in water purification.

Unique Carbonate-Based Single Ion Conducting Block Copolymers Enabling High-Voltage, All-Solid-State Lithium Metal Batteries.

Safety and high-voltage operation are key metrics for advanced, solid-state energy storage devices to power low- or zero-emission HEV or EV vehicles. In this study, we propose the modification of single-ion conducting polyelectrolytes by designing novel block copolymers, which combine one block responsible for high ionic conductivity and the second block for improved mechanical properties and outstanding electrochemical stability. To synthesize such block copolymers, the ring opening polymerization (ROP) of trimethylene carbonate (TMC) monomer by the RAFT-agent having a terminal hydroxyl group is used. It allows for the preparation of a poly(carbonate) macro-RAFT precursor that is subsequently applied in RAFT copolymerization of lithium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethylsulfonyl)imide and poly(ethylene glycol) methyl ether methacrylate. The resulting single-ion conducting block copolymers show improved viscoelastic properties, good thermal stability (Tonset up to 155 °C), sufficient ionic conductivity (up to 3.7 × 10–6 S cm–1 at 70 °C), and high lithium-ion transference number (0.91) to enable high power. Excellent plating/stripping ability with resistance to dendrite growth and outstanding electrochemical stability window (exceeding 4.8 V vs Li+/Li at 70 °C) are also achieved, along with enhanced compatibility with composite cathodes, both LiNiMnCoO2 – NMC and LiFePO4 – LFP, as well as the lithium metal anode. Lab-scale truly solid-state Li/LFP and Li/NMC lithium-metal cells assembled with the single-ion copolymer electrolyte demonstrate reversible and very stable cycling at 70 °C delivering high specific capacity (up to 145 and 118 mAh g–1, respectively, at a C/20 rate) and proper operation even at a higher current regime. Remarkably, the addition of a little amount of propylene carbonate (∼8 wt %) allows for stable, highly reversible cycling at a higher C-rate. These results represent an excellent achievement for a truly single-ion conducting solid-state polymer electrolyte, placing the obtained ionic block copolymers on top of polyelectrolytes with highest electrochemical stability and potentially enabling safe, practical Li-metal cells operating at high-voltage.

(Invited) Towards Obtaining Rotating Disk Electrode Activity in a Membrane Electrode Assembly; Implications of the Electrocatalyst-Ionomer Interface for the Oxygen Reduction Reaction

The proper integration of materials to enable high performing low temperature fuel cell operation has never been more crucial to realizing the isolated (e.g. half-cell or ex-situ) improvements of advanced electrocatalysts, supports and ionomers in an effort to maximize efficiency and fuel. This integration pathway for oxygen reduction electrocatalysts, from initial testing in a rotating disk electrode (RDE) to their apex form as porous electrodes in a membrane electrode assembly (MEA), is replete with potential pitfalls. Along the route to improving MEA level electrocatalyst kinetics and electrode transport properties are numerous choices relating to ink formulation (i.e. solvents and solvent ratios), ink processing and deposition methodology, ionomer content and chemistry and electrochemical MEA conditioning. Combined with carbon morphology/porosity, such variables can alter the final electrode morphology, influencing active site accessibility and ORR activity as well as oxygen transport resistance and electrode proton conductivity.[1–5]Here, the development and utilization of in situ diagnostics designed to probe specific phenomena (e.g. catalyst/ionomer interactions, molecular and Knudsen diffusion, electrochemical active site accessibility and catalyst layer proton resistance) will be presented as tools to contrast the ink, processing and fabrication methods necessary to achieve high performance PGM (e.g. Pt/C and Pt alloy/C) and PGM-free (e.g. FeNx/C) electrocatalysts based electrodes. For PGM based MEAs, the dynamic effects of electrochemical conditioning will be examined in an effort to both baseline MEA level performance and decouple the contributions of simultaneous electrocatalyst particle growth and the removal of system impurities.[6] The prerequisite understanding gleaned from the application of electrochemical diagnostics and MEA conditioning procedures will be combined with the development of a novel sulfonated ionic liquid block copolymer ionomer and tailored integration methodology to illustrate a pathway towards improved MEA level performance.[7]References[1] A. Orfanidi, P.J. Rheinlander, N. Schulte, H.A. Gasteiger, Ink Solvent Dependence of the Ionomer Distribution in the Catalyst Layer of a PEMFC, Journal of The Electrochemical Society. (2018) 11.[2] S. Khandavalli, J.H. Park, N.N. Kariuki, D.J. Myers, J.J. Stickel, K. Hurst, K.C. Neyerlin, M. Ulsh, S.A. Mauger, Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks, ACS Appl. Mater. Interfaces. (2018) 13.[3] D.A. Cullen, R. Koestner, R.S. Kukreja, Z.Y. Liu, S. Minko, O. Trotsenko, A. Tokarev, L. Guetaz, H.M. Meyer, C.M. Parish, K.L. More, Imaging and Microanalysis of Thin Ionomer Layers by Scanning Transmission Electron Microscopy, J. Electrochem. Soc. 161 (2014) F1111–F1117. https://doi.org/10.1149/2.1091410jes.[4] T. Van Cleve, S. Khandavalli, A. Chowdhury, S. Medina, S. Pylypenko, M. Wang, K.L. More, N. Kariuki, D.J. Myers, A.Z. Weber, S.A. Mauger, M. Ulsh, K.C. Neyerlin, Dictating Pt-Based Electrocatalyst Performance in Polymer Electrolyte Fuel Cells, from Formulation to Application, ACS Appl. Mater. Interfaces. 11 (2019) 46953–46964. https://doi.org/10.1021/acsami.9b17614.[5] G. Wang, L. Osmieri, A.G. Star, J. Pfeilsticker, K.C. Neyerlin, Elucidating the Role of Ionomer in the Performance of Platinum Group Metal-free Catalyst Layer via in situ Electrochemical Diagnostics, J. Electrochem. Soc. 167 (2020) 044519. https://doi.org/10.1149/1945-7111/ab7aa1.[6] S. Kabir, D.J. Myers, N. Kariuki, J. Park, G. Wang, A. Baker, N. Macauley, R. Mukundan, K.L. More, K.C. Neyerlin, Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study, ACS Appl. Mater. Interfaces. 11 (2019) 45016–45030. https://doi.org/10.1021/acsami.9b11365.[7] Y. Li, T.V. Cleve, R. Sun, R. Gawas, G. Wang, M. Tang, Y.A. Elabd, J. Snyder, K.C. Neyerlin, Modifying the Electrocatalyst−Ionomer Interface via Sulfonated Poly(ionic liquid) Block Copolymers to Enable High- Performance Polymer Electrolyte Fuel Cells, ACS Energy Letters 5 (2020) 1726-1731.

Asymmetric Reactions in Water Catalyzed by L-Proline Tethered on Thermoresponsive Ionic Copolymers

L-Proline was covalently tethered on thermoresponsive ionic block copolymers that formed micelles in aqueous solutions. The block copolymers consisted of a poly(N-isopropylacrylamide) (PNIPAAm) segment and an anionic or cationic polymer segment. These copolymers exhibited lower critical solution temperature (LCST) behavior at ca. 35-40°C, and achieved thermal stimuli-induced formation and dissociation of micelles. The copolymer generated micelles in aqueous solution at a higher temperature, where a catalytic aldol reaction proceeded with high diastereo- and enantioselectivities. The micelles dissociated at lower temperature to form a clear solution such that the products could be efficiently extracted from the aqueous reaction mixture. Extraction of the aldol product with an organic solvent from the aqueous solution of the anionic copolymer was more efficient than from the nonionic copolymer solution.

Polymerized Ionic Liquid Block Copolymer Electrolytes for All-Solid-State Lithium-Metal Batteries

In this work, we present a polymerized ionic liquid block copolymer (PBCP) film where relevant properties such as ionic conductivity and electrochemical parameters are tailored by using a ternary system comprised of poly(styrene-b-1-((2-acryloyloxy)ethyl)−3-butylimidazolium bis(tri-fluoromethanesulfonyl)imide), LiFSI salt and ethylene carbonate (EC) as a cosolvent. It was found that EC efficiently decreases the glass transition temperature of the ionic block, resulting in an improved ionic conductivity and efficient platting/stripping of lithium. By using an optimal ratio of EC/LiFSI at relatively high LiFSI amount, Li∣Li symmetrical cells at 50 °C show an overpotential as low as 70 mV at 0.1 mA.cm−2 along with a high lithium transport number of 0.56 (tLi+). All-solid-state full cells based on lithium iron phosphate cathode paired with a lithium metal anode reveal a rather stable cycling at both 50 °C and 70 °C. A negligible capacity fading is observed up to 30 cycles where a specific capacity as high as 161 mAh.g−1 is achieved with a coulombic efficiency of 99.9%. Thus, this work demonstrates an important pathway for tailoring the properties of solid state polymer electrolytes for emerging and specially designed block copolymer architectures comprising domains that give both excellent ionic conduction along with desirable mechanical properties.

Unipolar Polymerized Ionic Liquid Copolymers as High-Capacitance Electrolyte Gates for n-Type Transistors

A series of well-defined polymerized ionic liquid (PIL) statistical and block copolymers consisting of ionic liquid monomer, 1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide, ...

Ionic Liquid Electrolytes – from Novel Separators to Solid Polymer Electrolytes

One of the significant challenges to the application of ionic liquid electrolytes (ILE’s) is the ability to identify separators that can be effectively ‘wetted’ by the electrolyte. There has been significant work in identifying appropriate commercial separators for these electrolytes, with varying degrees of success [1]. To-date, the most effective separator for ILE’s is glass fibre, however, this material has large, open pore structure and this requires it to relatively thick to prevent short circuits between the electrodes. As a consequence, there is a need to identify new materials / structures that can lead to innovative separators that can allow ILE’s to be effectively used in batteries. To this end, we have examined the use of a “supported” electrospun membrane to be able to “tailor” the interfaces of the electrodes, but also allow effective wetting of the separator with an ILE to enable use in a lithium-ion battery [1]. However, in doing this, we have now made a “simple” separator far more complex in order to address the ILE wetting problem. So the question needs to be asked – can we combine the properties of the complex separator with an ILE into one solution, such as a solid polymer electrolyte? Further, can we improve these materials by exploiting micro-phase structured morphologies to provide us with enhanced mechanical properties as well? One type of these micro-phase structured polymers [2], known as PILBlox, is made of a high Tg block for mechanical strength and a low Tg ionic block for ionic conductivity [3, 4]. Combining PILBlox with a lithium based ionic salt and an ionic liquid forms a polymer electrolyte which ideally maintains the micro-phase separation present of the pure PILBlox polymer, and confines the ionic salt and ionic liquid to the ionic block of the polymer [4, 5]. In this presentation, we will describe our efforts to make innovative separators using electrospinning techniques and the resulting electrochemistry, before turning our attention to the PILBlox materials and examining their physical properties and their potential use in solid state batteries. References Francis. C., et al., manuscript in preparation, 2018.Bates, F.S., Polymer-Polymer Phase-Behavior. Science, 1991. 251(4996): p. 898-905.Dean, J.M., et al., Micellar structure and mechanical properties of block copolymer-modified epoxies. Journal of Polymer Science Part B-Polymer Physics, 2001. 39(23): p. 2996-3010.Nykaza, J.R., et al., Polymerized ionic liquid diblock copolymer as solid-state electrolyte and separator in lithium-ion battery. Polymer, 2016. 101: p. 311-318.Meek, K.M. and Y.A. Elabd, Polymerized ionic liquid block copolymers for electrochemical energy. Journal of Materials Chemistry A, 2015. 3(48): p. 24187-24194.

Cover Feature: Enabling High Lithium Conductivity in Polymerized Ionic Liquid Block Copolymer Electrolytes (Batteries & Supercaps 2/2019)

Cover Feature: Enabling High Lithium Conductivity in Polymerized Ionic Liquid Block Copolymer Electrolytes (Batteries & Supercaps 2/2019)

A novel luminescent sensor for disaccharide detection in food: Synthesis and application of a water-soluble rod-coil ionic block copolymer

A simple and low cost method for detecting disaccharide in food product is important for people who need control the consumption of saccharides in daily life. In this study, a water soluble rod-coil ionic block copolymer poly[2,7-(9,9-dihexyl-fuorene)]-b-cationic quaternized-poly[2-(dimethylamino)ethyl methacrylate] (PF-b-PDI) was employed as luminescent sensor for detection of lactose, sucrose and maltose in food. It was found that the PF-b-PDI could emit vision fluorescence with the existence of hydroquinone (HQ) in aqueous, but would be quenched by the oxidization of hydrogen peroxide (H2O2). The glucose oxidase (GOx) could be used for catalyzing the glucose to generate the H2O2. And the sucrase, maltase and lactase could respectively catalyze sucrose, maltose and lactose to glucose. With the selectivity and catalyst of enzyme, the PF-b-PDI aqueous blend with HQ showed fluorescence sensitive to sucrose, maltose and lactose with detection limit value of 1.36 μM, 1.09 μM and 3.08 μM, respectively. Moreover, the detection of lactose in milk samples by this method just revealed 0.44% of average deviation compared to standard lactose solution, which mean this method was suitable for detecting lactose in milk.