High-performance Polymer Electrolyte Research Articles

Modifying Li+ and Anion Diffusivities in Polyacetal Electrolytes: A Pulsed-Field-Gradient NMR Study of Ion Self-Diffusion

Polyacetal electrolytes have been demonstrated as promising alternatives to liquid electrolytes and poly(ethylene oxide) (PEO) for rechargeable lithium-ion batteries; however, the relationship between polymer structure and ion motion is difficult to characterize. Here, we study structure–property trends in ion diffusion with respect to polymer composition for a systematic series of five polyacetals with varying ratios of ethylene oxide (EO) to methylene oxide (MO) units, denoted as P(xEO-yMO), and PEO. We first use 7Li and 19F pulsed-field-gradient NMR spectroscopy to measure cation and anion self-diffusion, respectively, in polymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt mixtures. At 90 °C, we observe modest changes in Li+ diffusivity across all polymer compositions, while anion (TFSI–) self-diffusion coefficients decrease significantly with increasing MO content. At a given reduced temperature (T – Tg), all polyacetal electrolytes exhibit faster Li+ self-diffusion than PEO. Intriguingly, P(EO-MO) and P(EO-2MO) also show slower TFSI– anion self-diffusion than PEO at a given reduced temperature. Molecular dynamics simulations reveal that shorter distances between acetal oxygen atoms (O–CH2–O) compared to ether oxygens (O–CH2–CH2–O) promote more diverse, often asymmetric, Li+ coordination environments. Raman spectra reveal that anion-rich ion clusters in P(EO-MO) and P(EO-2MO) lead to decreased anion diffusivity, which along with increased cation diffusivity, support the viability of polyacetals as high-performance polymer electrolytes.

High-performance polymer electrolyte membrane modified with isocyanate-grafted Ti3+ doped TiO2 nanowires for lithium batteries

The Ti3+ doped TiO2 nanowires were grafted by tolylene-2,4- diisocyanate (TDI) and applied as a modifier for the preparation of organic–inorganic hybrid electrolyte in high performing lithium batteries. The PEO-based polymer electrolyte was optimized at different organic–inorganic ratios and exhibited excellent lithium-ion conductivity of 1 × 10−4 S·cm−1 at 30 °C when adding 8% TDI-TiO2 nanowires, outstanding electrochemical stability with a wide electrochemical window up to 5.5 V at 60 °C and a high lithium-ion transport number of 0.36. The LiFePO4|PTTNW8%|Li cells deliver excellent rate capability and cycling performance, with a high initial discharge capacity up to 151 mAh·g−1 at 60 °C at 0.1 C rate and excellent capacity retention of 91% after 100th cycle. NCM811|PTTNW8%|Li high-voltage lithium batteries were also demonstrated at a 50 °C, which displayed a superior cycling performance. Therefore, the prepared PEO-TDI-TiO2 electrolyte is a promising polymer electrolyte for solid- state lithium batteries.

High-performance gel polymer electrolytes derived from PAN-POSS/PVDF composite membranes with ionic liquid for lithium ion batteries

The gel polymer electrolytes (GPEs) with poly(acrylonitrile-polyhedral oligomeric silsesquioxane)/poly(vinylidene fluoride) (PAN-POSS/PVDF) blends as free-standing porous membrane and ionic liquid (IL) as absorption substance were successfully prepared. By tuning the content of PAN-POSS, the porosity and absorptivity of the blended membranes could be regulated. Due to the higher porosity and absorptivity, the ionic conductivity of GPEs with 15 wt% PAN-POSS reaches to 1.91 × 10−3 S cm−1 at 20 oC. Meanwhile, the electrolytes also show excellent mechanical properties, thermal stability, and fire resistance. More importantly, the high electrochemical window of 4.6 V (vs. Li/Li+) has been acquired and the testing cells with Li metal anode and LiFePO4 cathode show a tolerable rate performance. Such prepared GPEs are expected to be applied to lithium batteries with high safety and electrochemical performance.

High-performance polymer electrolyte membranes incorporated with 2D silica nanosheets in high-temperature proton exchange membrane fuel cells

Silica nanosheets (SN) derived from natural vermiculite (Verm) were successfully incorporated into polyethersulfone–polyvinylpyrrolidone (PES–PVP) polymer to fabricate high–temperature proton exchange membranes (HT–PEMs). The content of SN filler was varied (0.1–0.75 wt%) to study its influence on proton conductivity, power density and durability. Benefiting from the hydroxyl groups of SN that enable the formation of additional proton–transferring pathways, the inorganic–organic membrane displayed enhanced proton conductivity of 48.2 mS/cm and power density of 495 mW/cm2 at 150 °C without humidification when the content of SN is 0.25 wt%. Furthermore, exfoliated SN (E–SN) and sulfonated SN (S–SN), which were fabricated by a liquid–phase exfoliation method and silane condensation, respectively, were embedded in PES–PVP polymer matrix by a simple blending method. Due to the significant contribution from sulfonic groups in S–SN, the membrane with 0.25 wt% S–SN reached the highest proton conductivity of 51.5 mS/cm and peak power density of 546 mW/cm2 at 150 °C, 48% higher than the pristine PES–PVP membranes. Compared to unaltered PES–PVP membrane, SN added hybrid composite membrane demonstrated excellent durability for the fuel cell at 150 °C. Using a facile method to prepare 2D SN from natural clay minerals, the strategy of exfoliation and functionalization of SN can be potentially used in the production of HT–PEMs.

Ultrathin Self-Cross-Linked Alkaline Polymer Electrolyte Membrane for APEFC Applications

Ultrathin alkaline polymer electrolyte (APE) membranes have become a hot research topic for high-performance alkaline polymer electrolyte fuel cells (APEFCs). To our knowledge, freestanding ultrathin membranes with thicknesses of or below 10 μm have never been reported for successful applications in APEFCs. The obstacle comes from the poor mechanical strength of the ultrathin membrane during the fuel cell assembly. Herein we report an ultrathin 10 μm membrane made of cross-linked quaternary ammonia poly(N-methylpiperidine-co-p-terphenyl), denoted cQAPPT. This ultrathin cQAPPT membrane is robust enough for fuel cell assembly and demonstrates a high H2/O2 peak power density of 1.85 W/cm2 at 80 °C.

Synergistic Effects of Plasticizer and 3D Framework toward High-Performance Solid Polymer Electrolyte for Room-Temperature Solid-State Lithium Batteries

Solid polymer electrolytes (SPEs) can alleviate the safety issues existing in commercialized lithium ion batteries with liquid electrolyte. However, the low room-temperature ionic conductivity and ...

Gas Diffusion Layers with Deterministic Structure for High Performance Polymer Electrolyte Fuel Cells.

Hydrogen-fed polymer electrolyte fuel cells (PEFCs) are promising electrochemical energy converters and a key technology for sustainable mobility and coupling energy sectors. Under operating conditions, water is produced by the oxygen reduction reaction. The gas diffusion layer (GDL) materials, interfacing the reaction sites and gas feed channels, play a key role in the water management. When water condenses in the GDL pore structure, the gas transport to the cathode catalyst layer is deteriorated, thus limiting the cell performance. State-of-the-art GDL materials are stochastic, porous media based on carbon fibers, where water and gas are transported on random, tortuous paths through the pore network. In this work, a novel approach based on a material with a deterministic structure, with a two-layered fabric, is presented. This material, with just one pore throat in the transport path, facilitates water transport and increases the effective diffusivity for gas transport through its open structure. Furthermore, the regular pattern opens up a wide range of tuning opportunities. The presented results demonstrate the improved water management, on the basis of X-ray tomographic image data, and superior cell performance of this novel class of materials, able to be adapted to the local channel geometry.

High performance polymer electrolyte membrane with efficient proton pathway over a wide humidity range and effective cross-linking network

It is vital to constructing long-term proton transfer channels with sufficient conduction sites in proton exchange membranes. The mPBI-TGDDM/ZrSP polymer electrolyte membranes are prepared by covalent cross-linking with tetrafunctional N,N,N′,N′-tetraglycidy-4,4′- diaminodiphenyl-methane (TGDDM) and doping with the zirconium 3-sulfopropyl phosphonate (ZrSP). The new high-temperature proton conductor ZrSP contains sulfonic acid groups and phosphonic acid groups. TGDDM has high functionality which efficiently enhanced the dimensional stability, mechanical properties, and oxidative resistance of the membranes under low cross-linking degrees (5%–10%). The low cross-linking degree and good mechanical stability also allow high doping levels of ZrSP and consequently high proton conductivity. At 100% relative humidity (RH), 50% RH and 0 RH, the proton conductivity of mPBI-TGDDM(5%)/ZrSP(50%) membrane is 0.127, 0.078 and 0.0186 S cm−1 at 180 °C, respectively. A large number of sulfonic and phosphonic acid groups in the membrane can establish an efficient proton pathway over a wide humidity range. High cross-linking will decrease the conductivity, and high doping will increase the conductivity, thus affecting the performance of the fuel cells. The mPBI-TGDDM/ZrSP membranes exhibited good methanol resistance and good membrane selectivity and thus the membranes have great application potential in direct methanol fuel cells (DMFCs).

Enhancing the electrochemical performance of a flexible solid-state supercapacitor using a gel polymer electrolyte

The development of high-performance polymer electrolytes will be a crucial research target for flexible solid-state supercapacitors (FSSCs). In this study, a flexible gel polymer electrolyte (GPE) was fabricated to enhance flexible solid-state supercapacitor (FSSC) performance and electrochemical stability. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide was used as ionic liquid (IL), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as a host polymer with Li1.5Al0.33Sc0.17Ge1.5(PO4)3 (LASGP) serving as ceramic filler to fabricate the GPE films. Scanning electron microscope (SEM) image confirmed that a homogeneous uniform phase with a smooth surface was formed as the ionic liquid was added into the host polymer solution. X-ray diffraction (XRD) patterns show that the PVDF-HFP blend has a semi-crystalline structure while its amorphous nature extended with the increasing amount of IL and LASGP ceramic fillers. The GPE film was used as the electrolyte and separator, due to its high ionic conductivity (7.8×10-2 S cm−1) and excellent thermal stability up to 346 ℃. The FSSC cell with LASGP ceramic filler exhibits a high specific capacitance (115.45 F g−1) with a specific energy density of 27.10 Wh kg−1 at 1 mA. These results indicate that a GPE film with an activated carbon electrode could be a candidate for FSSC applications.

Fabrication and Electrolyte Characterizations of Nanofiber Framework-Based Polymer Composite Membranes with Continuous Proton Conductive Pathways.

For future fuel cell operations under high temperature and low- or non-humidified conditions, high-performance polymer electrolyte membranes possessing high proton conductivity at low relative humidity as well as suitable gas barrier property and sufficient membrane stability are strongly desired. In this study, novel nanofiber framework (NfF)-based composite membranes composed of phytic acid (Phy)-doped polybenzimidazole nanofibers (PBINf) and Nafion matrix electrolyte were fabricated through the compression process of the nanofibers. The NfF composite membrane prepared from the pressed Phy-PBINf showed higher proton conductivity and lower activation energy than the conventional NfF composite and recast-Nafion membranes, especially at low relative humidity. It is considered that the compression process increased the nanofiber contents in the composite membrane, resulting in the construction of the continuously formed effective proton conductive pathway consisting of the densely accumulated phosphoric acid and sulfonic acid groups at the interface of the nanofibers and the Nafion matrix. Since the NfF also improved the mechanical strength and gas barrier property through the compression process, the NfF composite polymer electrolyte membranes have the potential to be applied to future fuel cells operated under low- or non-humidified conditions.

Tuning the electronic structure of nanoporous Ag via alloying effect from Cu to boost the ORR and Zn-air battery performance

The Ag-based materials are drawing successive attentions as cathode for oxygen reduction reaction (ORR) towards high performance metal-air batteries and polymer electrolyte membrane fuel cells. Its catalytic performance has been profoundly influenced by the active sites and mass transportation channels. Herein, nanoporous AgCu (NP-AgCu) catalysts are fabricated by tuning the Ag/Cu ratio to optimize its electronic structure. The XRD and XPS results demonstrate that the d-band center of Ag moves closer to the Fermi level owing to the alloying effect from Cu. Adopted as electrocatalyst, NP-Ag4Cu exhibits a 7-fold enhancement in oxygen reduction activity as compared to NP-Ag. Upon potential cycling and chronoamperometry, NP-Ag4Cu also presents better stability after 5000 cycles and 20000 s than Pt/C. The NP-Ag4Cu was also used as cathode for Zn-air battery and demonstrate a power density of 151.5 mW cm−2, which compares favorably to that of NP-Ag (83.8 mW cm−2) ascribed to the improved cathodic activity. The present study provides a facile way to boost the ORR performance of Ag-based electrocatalyst and promote its applications in Zn-air batteries.

Functional polyethylene glycol-based solid electrolytes with enhanced interfacial compatibility for room-temperature lithium metal batteries

A high-performance solid polymer electrolyte with enhanced interfacial compatibility was synthesized via an in situ polymerization of functional polyethylene glycol combined with the in situ formation of stable SEI layers by vinylene carbonate.

Inexpensive gram scale synthesis of porous Ti4O7 for high performance polymer electrolyte fuel cell electrodes.

As a fuel cell catalyst support, more than 2 g of Magnéli phase Ti4O7 fine-particles were synthesized in a single reaction via an inexpensive route. The single-cell performance reached that of commercial carbon-supported platinum, with an excellent load cycle durability, one of the highest ever reported for oxide-supported platinum catalysts.

Ionic Conductivity of Protonated Layered Titanate Nano-Powder Compact in Water

Ion-conducting materials are significantly important for electrochemical energy conversion. In particular, proton-conducting polymer electrolyte has been commercialized in a wide range of residential-type fuel cells and hydrogen fuel-cell vehicles. In the way, Nafion have been extensively used for polymer electrolyte membrane (PEM) fuel cell and water electrolysis, however, it has few drawbacks including high production cost, low proton-conductivities and low humidity at high temperature (>100 °C). Recently, huge research efforts have been focused on the investigation of a new proton conducting inorganic electrolyte materials as an alternative to polymer-based membranes. Hence, we have demonstrated that nano-powder of a layered protonated titanate (H2Ti2O5.H2O; LPT) compound exhibits a significant proton conductivity and that the conduction has been identified to take place on the surface of the nanoparticles in contact with water. The conductivity was measured on the compact of the un-milled/milled powder and it reached higher than 10-2 S cm-1 at 95 °C in water in the milled case. The increase in conductivity of LPT after bead milling along with the thermogravimetric and surface area analysis suggested that the protonic conduction takes place on the surface of the nanoparticles in contact with water. A linear relationship was found between the BET surface area and electrical conductivity, indicating that the majority of proton conduction take place on the surface of titanates nanoparticles. However, the conductivity of LPT was still low (~10-2 Scm-1) compared to conventional electrolyte materials, such as Nafion other high-performance polymer electrolytes (~10-1 Scm-1). Nevertheless, the present conductivity of LPT is equivalent to 100 mΩ at 10 µm thick per cm2, which is applicable to water electrolysis and fuel cells. This work has demonstrated a great potential of using cheap and inorganic LPT materials as electrolyte materials in energy conversion applications. Figure 1

Electrochemical method to quantitate gas transport resistance at immediate vicinity of catalyst surface in polymer electrolyte fuel cells

Reduction in the gas transport resistance in the immediate vicinity of the interface between the catalyst metal and the ionomer thin film is one of the primary challenges in achieving high-performance polymer electrolyte fuel cells with a low use of precious metals. In this study, a new electrochemical method was developed to evaluate the transport resistance separately from any other resistances in a porous electrode using only a single target sample. The transport resistance lying on the catalyst surface was evaluated from its inversely proportional dependence on the active surface area, which is controlled by an adsorbate that deactivates the catalyst surface; moreover, its coverage is quantifiable and controllable. After the coverage control, the limiting current technique provides the transport resistance of a catalyst layer. As a demonstration, an oxygen transport resistance lying on a Pt-surface in a Pt/C catalyst layer was investigated using CO as an adsorbate. The resistance lying on the Pt-surface was successfully evaluated from the CO-coverage dependence of the catalyst layer resistance. In particular for the reactant gas of oxygen, CO is not suitable for blocking the adsorbate over 40 °C, and another candidate that does not interfere with O2 is required.

Role of Additives for High Performance Polymer Electrolytes

Today, the progress of polymer electrolytes with high ambient ionic conductivity, better mechanical and thermal properties, has become the main objective in the field of polymer science because of their requirements in super capacitors, rechargeable batteries, fuel cells and other electrochemical devices. Many kinds of polymer electrolytes have been developed, however main drawback is the low ionic conductivity, which is inadequate for most of the device applications. Efforts have also been made to enhance the ionic conductivity of polymer electrolytes to meet the demand for different devices. Although polymer electrolytes with high value of ionic conductivity (∼10−3-10−4 S/cm) have been developed but these also suffer from poor mechanical properties. Incorporation of plasticizers as well as nano fillers in polymer electrolytes, is of great importance for enhancing their performance in devices. In the recent years, researchers came up with an idea to make the use of ionic liquids in polymer electrolytes to address the problem of low ionic conductivity of polymer electrolytes at room temperatures as well as to keep good electrochemical and mechanical properties. The optimized ionic conductivity value of the order of ∼10−3 S/cm has been observed by different workers at different concentrations of ionic liquids. Also, polymer gel electrolytes have been reported to possess high ionic conductivity (of the order of ∼ 10−2 S/cm) at ambient temperature. However, despite possessing high value of ionic conductivity these gel electrolytes have poor mechanical and thermal properties. Hence, the modified polymer /gel electrolytes having optimized properties, are described in this review paper. An attempt has also been made to highlight the work of different researchers in the form of synthesis, characterization and analysis of different modified polymer electrolytes for their use in different ionic devices.

Spatially graded porous transport layers for gas evolving electrochemical energy conversion: High performance polymer electrolyte membrane electrolyzers

Decarbonizing society’s energy infrastructure is foundational for a sustainable future and can be realized by harnessing renewable energy for clean hydrogen and on-demand power with fuel cells. Here, we elucidate how graded porous transport layers (PTLs) are instrumental for high performance gas evolving electrochemical energy conversion devices, with an emphasis on polymer electrolyte membrane (PEM) electrolyzers. Spatially graded PTLs fabricated by vacuum plasma spraying are examined via in operando neutron imaging, electrochemical characterization, and pore network modelling. The results reveal the staggering benefits of positioning the lower porosity region adjacent to the catalyst layer and the higher porosity region adjacent to the flow field, which lead to current densities up to 4.5 A/cm2 with a 29 % reduction in cell potential, 38 % reduction in mass transport overpotential, and 50 % reduction in PTL gas saturation. The liquid water permeability of the PTL also enhances by an order of magnitude, with a drastic reduction in gas saturation adjacent to the catalyst layer. Custom graded PTLs have the potential to transform performance levels for a broad array of gas evolving electrochemical energy conversion devices.

Facile Airbrush Fabrication of Gas Diffusion Layers Comprising Fine-Patterned Hydrophobic Double-Layer and Hydrophilic Channel for Improved Water Removal in Polymer Electrolyte Membrane Fuel Cells

We develop a facile and eco-friendly airbrush-based method for the fabrication of gas diffusion layers (GDLs) with improved water removal characteristics for high-performance polymer electrolyte membrane fuel cells (PEMFCs). The GDL architecture airbrushed on a porous carbon paper uniquely comprises hydrophobic double-layer coating and fine-patterned hydrophilic channels, which facilitate the outbound penetration of water generated from inside the membrane electrode assembly without flooding or undesirable mingling with oxygen inflow. We first prepare the colloids and solutions suitable for airbrushing, optimize the airbrush coating structure based on the water contact angle measurements, and finally confirm the improved water removal characteristics of the fabricated GDL samples by measuring the water transuding times. Our GDL fabrication procedure based on simple and fast airbrushing does not require costly vacuum process or toxic chemical treatment, thus may benefit practical and scalable manufacturing of high-performance PEMFCs towards the next-generation green transportation.

Modifying the Electrocatalyst-Ionomer Interface via Sulfonated Poly(ionic liquid) Block Copolymers to Enable High-Performance Polymer Electrolyte Fuel Cells.

Polymer electrolyte membrane fuel cell (PEMFC) electrodes with a 0.07 mgPt cm-2 Pt/Vulcan electrocatalyst loading, containing only a sulfonated poly(ionic liquid) block copolymer (SPILBCP) ionomer, were fabricated and achieved a ca. 2× enhancement of kinetic performance through the suppression of Pt surface oxidation. However, SPILBCP electrodes lost over 70% of their electrochemical active area at 30% RH because of poor ionomer network connectivity. To combat these effects, electrodes made with a mix of Nafion/SPILBCP ionomers were developed. Mixed Nafion/SPILBCP electrodes resulted in a substantial improvement in MEA performance across the kinetic and mass transport-limited regions. Notably, this is the first time that specific activity values determined from an MEA were observed to be on par with prior half-cell results for Nafion-free Pt/Vulcan systems. These findings present a prospective strategy to improve the overall performance of MEAs fabricated with surface accessible electrocatalysts, providing a pathway to tailor the local electrocatalyst/ionomer interface.

Effect of incorporation of zinc oxide nanoparticles on properties of PEMA based polymer electrolyte

High performance Polymer electrolytes are widely discussed nowadays on account of their physical and electrochemical properties. The present work involves modification of structural and electrical properties of PEMA based plasticised polymer electrolyte by incorporation by nano sized zinc oxide nanoparticle. It has been observed that the overall value of conductivity increased almost by 100 times when varying concentration of zinc oxide nanoparticles was added to matrix. Complex Impedence spectroscopy was used to measure the conductivity of the fabricated nano composites using various cole–cole plot. Perfect complexations among various components are affirmed by FTIR studies while XRD confirmed the variation in crystallinity of the prepared sample. Surface morphology of the samples was studied using Scanning Electron Microscopy.