High-performance Poly(biphenyl piperidinium) Type Anion Exchange Membranes with Interconnected Ion Transfer Channels: Cooperativity of Dual Cations and Fluorinated Side Chains

The performance of alkaline fuel cells is severely limited by substandard anion exchange membranes (AEMs) due to the lower ionic conductivity compared to the proton exchange membranes. The ionic conductivity of AEMs can be effectively improved by regulating the microphase structure, but it still cannot meet the practical use requirements. Here, enhanced microphase-separated structures are constructed by the cooperativity of highly hydrophilic dual cations and highly hydrophobic fluorinated side chains. Meanwhile, the introduction of  O enhances the flexibility of side chains and facilitates the formation of ion transport channels. The dual piperidinium cation functionalized membrane (PB2Pip-5C8F) which is grafted with the ultra-hydrophobic fluorocarbon chain exhibits a high conductivity of 74.4 mS cm⁻¹ at 30 °C and 168.46 mS cm⁻¹ at 80 °C. Furthermore, the PB2Pip-5C8F membrane achieves the highest peak power density of 718 mW cm⁻² at 80 °C under a current density of 1197 mA cm⁻² without back pressure. A long-term life cell test of this AEM shows a low voltage decay rate of 1.68 mV h⁻¹ over 70 h of operation at 80 °C.     

High Performance Anion Exchange Membranes with Confined Sub-2-nm Ion Channel

As a key component of low-cost anion exchange membrane fuel cells (AEMFCs), anion exchange membranes (AEMs) are far from commercial application, because of dissatisfactory alkaline stability and conductivity. Herein, a new insight is proposed to prepare high performance AEMs by constructing of confined ion channel. With an intermediate oligomer produced before the main copolymerization, novel poly(vinyl-carbazolyl aryl piperidinium) AEMs with confined sub-2-nm ion channel are successfully prepared. The unique sub-2-nm ion channel enable membranes ultrahigh hydroxide conductivity of 261.6 mS cm⁻¹, and the state-of-the-art chemical stability over 5000 h. Moreover, the AEMs also exhibit good mechanical stability with lower water uptake and dimensional swelling. Based on the as-prepared AEMs and ionomer, fuel cells exhibit outstanding peak power density of 1.8 and 0.2 W cm⁻² with Pt-based catalysts and completely non-precious metal catalysts, respectively.     

High Performance Anion Exchange Membrane Fuel Cells Enabled by Fluoropoly(olefin) Membranes

Although the peak power density of anion exchange membrane fuel cells (AEMFCs) has been raised from ≈0.1 to ≈1.4 W cm^?2 over the last decade, a majority of AEMFCs reported in the literature have not been demonstrated to achieve consistently high performance and steady‐state operation. Poly(olefin)‐based AEMs with fluorine substitution on the aromatic comonomer show considerably higher dimensional stability compared to samples that do not contain fluorine. More importantly, fluorinated poly(olefin)‐based AEMs exhibit high hydroxide conductivity without excessive hydration due to a new proposed mechanism where the fluorinated dipolar monomer facilitates increased hydroxide dissociation and transport. Using this new generation of AEMs, a stable, high‐performance AEMFC is operated for 120 h. When the fuel cell configuration is subjected to a constant current density of 600 mA cm^?2 under H₂/O₂ flow, the cell voltage declines only 11% (from 0.75 to 0.67 V) for the first 20 h during break‐in and the cell voltage loss is low (0.2 mV h^?1) over the subsequent 100 h of cell testing. The ease of synthesis, potential for low‐cost commercialization, and remarkable ex situ properties and in situ performance of fluoropoly(olefin)‐based AEM renders this material a benchmark membrane for practical AEMFC applications.     

Anion Exchange Membranes for Fuel Cells: Equilibrium Water Content and Conductivity Characterization

The ionic conductivity of anion exchange membranes (AEMs) directly determines the performance of anion exchange membrane fuel cells (AEMFCs), which highly depends on the hydration level of the membrane. A better understanding of the relationship between hydration level and membrane ionic conductivity is essential for membrane development and for water and thermal management analyses of AEMFCs. In this study, the effects of water activity and temperature on water uptake, equilibrium water content, and ionic conductivity of three high-performance AEMs (Alkymer, Orion, and Pention) are quantitatively characterized via the designed experiments. The results show that Orion exhibits the lowest water uptake and highest ionic conductivity among the three membranes at high water activity and Alkymer exhibits good water-retention capability and the highest ionic conductivity at low water activity. Empirical equations combining water activity and equilibrium water content are proposed based on fitted experimental data to define the hydration level. Empirical equations combining ionic conductivity, equilibrium water content, and temperature are fitted to illustrate the relationship between ionic conductivity and hydration level. The findings of this study can provide solid guidelines and support for the future experimental characterization and water and thermal management analyses of AEMFCs.     

A New Lithium‐Ion Conductor LiTaSiO5: Theoretical Prediction,Materials Synthesis,and Ionic Conductivity

Owing to the nonleakage and incombustibility, solid electrolytes are crucial for solving the safety issues of rechargeable lithium batteries. In this work, a new class of solid electrolyte, acceptor‐doped LiTaSiO₅, is designed and synthesized based on the concerted migration mechanism. When Zr⁴⁺ is doped to the Ta⁵⁺ sites in LiTaSiO₅, the high‐energy lattice sites are partly occupied by the introduced lithium ions, and the lithium ions at those sites interact with the lithium ions placed in the low‐energy sites, thereby favoring the concerted motion of lithium ions and lowering the energy barrier for ion transport. Therefore, the concerted migration of lithium ions occurs in Zr‐doped LiTaSiO₅, and a 3D lithium‐ion diffusion network is established with quasi‐1D chains connected through interchain channels. The lithium‐ion occupation, as revealed by ab initio calculations, is validated by neutron powder diffraction. Zr‐doped LiTaSiO₅ electrolytes are successfully synthesized; Li_1.1Ta_0.9Zr_0.1SiO₅ shows a conductivity of 2.97 × 10^?5 S cm^?1 at 25 °C, about two orders of magnitude higher than that of LiTaSiO₅, and it increases to 3.11 × 10^?4 S cm^?1 at 100 °C. This work demonstrates the power of theory in designing new materials.     

Ultra-Stable,Highly Proton Conductive,and Self-Healing Proton Exchange Membranes Based On Molecule Intercalation Technique and Noncovalent Assembly Nanostructure

Proton exchange membranes (PEMs) that can heal mechanical damage to restore original functions are imperative for fabricating reliable and durable proton exchange membrane fuel cells (PEMFCs). Here, an ultra-stable, highly proton conductive self-healing PEM via hydrogen-bonding complexation between Nafion and poly(vinyl alcohol) (PVA) followed by incorporation of sodium lignosulfonate (SLS) intercalation-modified graphene oxide (GO) and post-modification with 4-formylbenzoic acid (FBA) is presented. Notably, the introduction of GO complexes and post-modification of FBA molecules effectively improves the stability of composite membranes and also participate in the establishment of proton-conducting nanochannels. Compared with recast Nafion, the FBA-Nafion/PVA@SLS/GO composite membranes exhibit enhanced mechanical properties (36.2 MPa at 104.8% strain) and higher proton conductivity (0.219 S cm⁻¹ at 80 °C-100% RH and 23.861 mS cm⁻¹ at 80 °C-33% RH, respectively). More importantly, the incorporated PVA gives the FBA-Nafion/PVA@SLS/GO composite membranes superior self-healing capabilities that can heal mechanical damage of several tens of micrometers in size and restore their original proton conductivity under the operating conditions of the PEMFCs. This study opens an avenue toward the development of reliable and durable PEM for PEMFCs.     

Porous Proton Exchange Membrane with High Stability and Low Hydrogen Permeability Realized by Dense Double Skin Layers Constructed with Amino tris (methylene phosphonic acid)

Porous proton exchange membranes (PEMs) with abundant porous structures show enhanced phosphoric acid (PA) doping levels and proton transport capability. However, the high PA loss rate and serious hydrogen cross-over lead to poor membrane stability. Enhancing the stability of PA-doped porous PEMs is therefore crucial for obtaining high-performance proton exchange membrane fuel cells. Herein, a porous polybenzimidazole membrane with dense double skin layers is reported using amino tris (methylene phosphonic acid) (ATMP) constructed. This membrane effectively alleviates hydrogen permeation and PA loss in a water/anhydrous environment and exhibits enhanced stability. Surprisingly, as an organic proton conductor, ATMP has strong hydrogen bonding with PA, leading to the formation of more continuous proton transport channels. Due to the dense double skin layers protection and the synergistic mass transfer of ATMP and PA, the porous membrane shows excellent proton conductivity (0.112 S cm⁻¹) and a H₂-O₂ fuel cell peak power density of 0.98 W cm⁻² at 160 °C. Moreover, it presents excellent fuel cell stability, with a voltage decay rate of only 5.46 µV h⁻¹. In addition, the porous membrane surpasses the traditional working temperature range, operating in the range of 80–220 °C. This study provides new insight into developing high-performance porous PEMs.     

Proton Conducting Phase‐Separated Multiblock Copolymers with Sulfonated Poly(phenylene sulfone) Blocks for Electrochemical Applications: Preparation,Morphology, Hydration Behavior,and Transport

A family of multiblock copolymers consisting of alternating fully sulfonated hydrophilic poly(phenylene sulfone) and hydrophobic poly(phenylene ether sulfone) segments are prepared and characterized. The multiblock copolymers are formed by the coupling of preformed hydrophilic and hydrophobic blocks using a specially designed coupling agent. The block lengths (degree of polymerization) of both segment types were varied in order to control the ion exchange capacity. Solution cast films show spontaneous nanophase separation leading to distinct bicontinuous morphologies with correlation lengths around 15 nm. The hydrophobic phase gives the membranes their advantageous viscoelastic properties even at high temperatures under both wet and dry conditions, while proton conductivity takes place within the hydrophilic phase. Since the properties of fully sulfonated poly (phenylene sulfone)s are locally preserved within the hydrophilic domain, the membranes show very high proton conductivity and high hydrolytic stability. The very high degree of water dispersion within the hydrophilic domains leads to very low electro‐osmotic water drag. Because of their superior transport and stability properties these multiblock copolymers have a great potential for use as a substitute for perfluorosulfonic acid membranes which are used as separator materials in electrochemical applications such as polymer electrolyte membrane (PEM) fuel cells and redox flow batteries.     

Re‐Engineering Poly(Acrylic Acid) Binder toward Optimized Electrochemical Performance for Silicon Lithium‐Ion Batteries: Branching Architecture Leads to Balanced Properties of Polymeric Binders

Silicon is a promising anode material for lithium‐ion batteries with its superior capacity. However, the drastic volume changes during lithiation/delithiation cycles hinder the cycling performance, resulting in particle pulverization, conductivity loss, and an unstable electrode–electrolyte interface. Herein, a series of synthetic polymeric binders, poly(acrylic acid‐co‐tetra(ethylene glycol) diacrylate)—featuring a poly(acrylic acid) (PAA) backbone branched via tetra(ethylene glycol) diacrylate (TEGDA)—are developed that edge toward evidencing well‐balanced properties to confront capacity fading in Si‐based electrodes. The incorporation of ether chain not only leads to the branching architecture of the PAA backbone, thus affecting its mechanical properties, but also promotes the conductivity of Li ions. As a result, a synergistic performance improvement is observed in both half and full cells. The best‐performing cell using a branched PAA binder (bPAA) with a feeding molar ratio ([TEGDA]:[acrylic acid(AA)]) of 0.2 results in a 10% increase in initial capacity and a 31% increase in capacity retention over 100 cycles compared to the linear PAA cell. The cross‐sectional microscopic images of the cycled electrodes reveal that bPAA binders can drastically reduce the electrode expansion. This improvement results from the well‐balanced properties of the polymer design, which could guide further development for more advanced binder materials.     

Synthesis of Nanofiber‐Based Silica Networks Mediated by Organized Poly(ethylene imine): Structure,Properties, and Mechanism

Linear poly(ethylene imine) (PEI) can self‐organize into fibrous aggregates with a crystalline core and a brushlike shell of ethyleneimine (EI) segments. Silicification from alkoxysilane mediated by PEI aggregates easily produces silica nanofibers (20–23 nm in diameter) with a core of axial, crystalline PEI filaments (5–7 nm in width) and a shell of silica (6–8 nm in thickness). Removing the axial filament of PEI from the silica nanofiber by calcination produces silica nanotubes. More interestingly, a nanowire‐like platinum lining is formed in the silica nanofiber—a result of the PEI filament's ability to reduce PtCl₄^2–. The degree of polycondensation, composition, and surface area of the resulting silica are investigated by ²⁹Si magic angle spinning NMR spectroscopy, elemental analysis, and N₂/He adsorption–desorption measurements. The time course of the reaction and the amount of silica source needed for silica‐fiber formation confirm that silica deposition occurs exclusively and site selectively on the surface of the organized, fibrous PEI. Thus, the fibrous aggregates of PEI appear to be highly suitable for depositing silica fibers from both tetramethoxysilane and tetraethoxysilane.