Rigid crosslinkers towards constructing highly-efficient ion transport channels in anion exchange membranes

Designing Highly Conductive Anion Exchange Membranes: Tuning Domain Continuity with ABC Block Copolymer Self-Assembly

Anion exchange membranes (AEMs) play a critical role in clean energy devices, and optimizing their performance requires a deeper understanding of morphology-performance relationships. This study investigates ABC triblock terpolymer AEMs to explore how domain continuity influences hydroxide conductivity, water uptake, and dimensional stability. High molecular weight ABC triblock terpolymers were synthesized through the controlled vinyl-addition polymerization of norbornene monomers functionalized with alkyl, benzyl, or bromobutyl substituents. Morphology was systematically varied across the series without significantly changing the molecular weight or ion exchange capacity (IEC) of the polymer by adjusting the alkyl/benzyl block length ratio. Solution-cast films exhibited either 2D-continuous lamellar or 3D-co-continuous network phase morphologies, with domain continuity largely retained after cationic functionalization. AEMs with 3D-co-continuous domains demonstrated superior performance, including enhanced dimensional stability and competitive hydroxide conductivities of up to 84 mS/cm at 25 °C and 131 mS/cm at 80 °C. This work highlights how the self-assembly of ABC triblock terpolymers can be leveraged to investigate morphology-performance relationships and achieve highly conductive, durable AEMs.

Rubbery Soft Polymer Electrolyte Membrane with a Nanomatrix Channel Prepared from Natural Rubber

Rubbery soft polymer electrolyte membranes (PEMs) prepared from naturally occurring products are in high demand for the fabrication of flexible fuel cells as a multipurpose energy source to achieve a carbon-neutral society. This work describes the preparation of a rubbery soft PEM from deproteinized natural rubber (DPNR) by grafting-copolymerizing ethyl p-styrenesulfonate (SSEt) onto the surface of rubber particles in the latex stage, followed by hydrolysis with NaOH and cast film formation to construct a nanomatrix channel. The resulting rubbery soft PEM, a graft copolymer of DPNR and poly(p-styrenesulfonic acid) (DPNR-graft-PSS), is characterized by 1H NMR spectroscopy, transmission electron microscopy (TEM), impedance analysis, and tensile testing. The hydrophobic rubber particles with a diameter of about 1 μm are well dispersed in the continuous nanochannel of hydrophilic poly(p-styrenesulfonic acid) with a thickness of about 10 nm that possesses a high proton conductivity, owing to an efficient proton transportation, which is beneficial for polymer electrolyte fuel cells. σ* is the proton conductivity per unit equivalent of sulfonic acid, which is distinguished from the proton conductivity, σ. The value of σ* for the DPNR-graft-PSS prepared with 1.0 mol/kg-rubber of SSEt is 2.6 (S/cm)/meq, which is approximately 1.4 times higher than that of the perfluorosulfonic acid membrane Nafion117, whereas its σ is lower. The apparent activation energy of DPNR-graft-PSS (3.2 kJ/mol) is lower than that of Nafion117, and its stress at break (6.9 MPa) is higher than that of DPNR. The high σ*, low apparent activation energy, and outstanding tensile strength of DPNR-graft-PSS can be attributed to the formation of the nanomatrix channel.

Ether-Free Alkaline Polyelectrolytes for Water Electrolyzers: Recent Advances and Perspectives

Anion exchange membrane (AEM) water electrolyzers (AEMWEs) have attracted great interest for their potential as sustainable, environmentally friendly, low-cost sources of renewable energy. Alkaline polyelectrolytes play a crucial role in AEMWEs, determining their performance and longevity. Because heteroatom-containing polymers have been shown to have poor durability in alkaline conditions, this review focuses on ether-free alkaline polyelectrolytes, which are more chemically stable. The merits, weaknesses, and challenges in preparing ether-free AEMs are summarized and highlighted. The evaluation of synthesis methods for polymers, modification strategies, and cationic stability will provide insights valuable for the structural design of future alkaline polyelectrolytes. Moreover, the in situ degradation mechanisms of AEMs and ionomers during AEMWE operation are revealed. This review provides insights into the design of alkaline polyelectrolytes for AEMWEs to accelerate their widespread commercialization.

Development and application of ordered membrane electrode assemblies for water electrolysis

With the development of hydrogen energy, there has been increasing attention toward fuel cells and water electrolysis. Among them, the zero-gap membrane electrode assembly (MEA) serves as an important triple-phase reaction site that determines the performance and efficiency of the reaction system. The development of efficient and durable MEAs plays a crucial role in the development of hydrogen energy. Consequently, a great deal of effort has been devoted to developing ordered MEAs that can effectively increase catalyst utilization, maximize triple-phase boundaries, enhance mass transfer and improve stability. The research progress of ordered MEAs in recent advances is highlighted, involving hydrogen fuel cells and low temperature water electrolysis technology. Firstly, the fundamental scientific understanding and structural characteristics of MEAs based on one-dimensional nanostructures such as nanowires, nanotubes and nanofibers are summarized. Then, the classification, preparation and development of ordered MEAs based on three-dimensional structures are summarized. Finally, this review presents current challenges and proposes future research on ordered MEAs and offers potential solutions to overcome these obstacles.

Twisted Poly(p-terphenyl-co-m-terphenyl)-Based Anion Exchange Membrane for Water Electrolysis

In order to improve the mechanical and water electrolysis performance of anion exchange membranes (AEMs), we adjusted the ratio between p-terphenyl and m-terphenyl to balance the backbone conformation, which gives it a better suitability for a better combination with cations. The results showed that poly(m-terphenyl-co-p-terphenyl)-based AEMs have excellent mechanical properties. Among them, the m-p-TP-40-BOP-ASU membrane has the highest tensile strength and elongation at break (75.72 MPa and 16.07%). The ionic conductivity reaches 137.14 mS cm-1 at 80 °C owing to the fact that efficient ion-conducting channels are formed by well-balanced molecular structures. The current density of the m-p-TP-40-BOP-ASU membrane reached 1.96 A cm-2 (1 M KOH aq, 2.0 V and 60 °C). After testing for 112 h under a current density of 500 mA cm-2, the voltage increased by 102 mV compared to the initial electrolysis voltage. All results have shown that m-p-TP-x-BOP-ASU has excellent electrolysis performance and electrochemical durability and has a promising application prospect in AEM water electrolyzers.

"Thiol-ene" crosslinked polybenzimidazoles anion exchange membrane with enhanced performance and durability

To address the "trade-off" between conductivity and stability of anion exchange membranes (AEMs), we developed a series of crosslinked AEMs by using polybenzimidazole with norbornene (cPBI-Nb) as backbone and the crosslinked structure was fabricated by adopting click chemical between thiol and vinyl-group. Meanwhile, the hydrophilic properties of the dithiol cross-linker were regulated to explore the effect for micro-phase separation morphology and hydroxide ion conductivity. As result, the AEMs with hydrophilic crosslinked structure (PcPBI-Nb-C2) not only had apparent micro-phase separation morphology and high OH^- conductivity of 105.54 mS/cm at 80 °C, but also exhibited improved mechanical properties, dimensional stability (swelling ratio < 15%) and chemical stability (90.22 % mass maintaining in Fenton's reagent at 80 °C for 24 h, 78.30 % conductivity keeping in 2 M NaOH at 80 °C for 2016 h). In addition, the anion exchange membranes water electrolysis (AEMWEs) using PcPBI-Nb-C2 as AEMs achieved the current density of 368 mA/cm² at 2.1 V and the durability over 500 min operated at 150 mA/cm² under 60 °C. Therefore, this work paves the way for constructing AEMs by introduction of norbornene into polybenzimidazole and formation of hydrophilic crosslinked structure based on "thiol-ene".

Tuning Alkaline Anion Exchange Membranes through Crosslinking: A Review of Synthetic Strategies and Property Relationships

Alkaline anion exchange membranes (AAEMs) are an enabling component for next-generation electrochemical devices, including alkaline fuel cells, water and CO2 electrolyzers, and flow batteries. While commercial systems, notably fuel cells, have traditionally relied on proton-exchange membranes, hydroxide-ion conducting AAEMs hold promise as a method to reduce cost-per-device by enabling the use of non-platinum group electrodes and cell components. AAEMs have undergone significant material development over the past two decades; however, challenges remain in the areas of durability, water management, high temperature performance, and selectivity. In this review, we survey crosslinking as a tool capable of tuning AAEM properties. While crosslinking implementations vary, they generally result in reduced water uptake and increased transport selectivity and alkaline stability. We survey synthetic methodologies for incorporating crosslinks during AAEM fabrication and highlight necessary precautions for each approach.

New block poly(ether sulfone) based anion exchange membranes with rigid side-chains and high-density quaternary ammonium groups for fuel cell application

We report a series of novel poly(ether sulfone) based anion exchange membranes (AEMs) with relatively good stability due to their rigid side-chains and heterocyclic quaternary ammonium groups. The AEMs show appropriate performance in AEM fuel cells.

Nanostructured high-performance electrolyte membranes based on polymer network post-assembly for high-temperature supercapacitors

The development of high-temperature supercapacitors highly relies on the explore of stable polymer electrolyte membranes (PEMs) with high ionic conductivities at high-temperature conditions. However, it is a challenge to achieve both high stability and high conductivity in a PEM at elevated temperatures. Herein, we report the fabrication of high-performance proton conductive PEMs suitable for high-temperature supercapacitors (HT-SCs), which is based on a post-assembly strategy to control the rearrangement of polymer networks in the PEMs. This strategy can create cross-linked PEMs with bicontinuous nanostructures, as well as highly stable and highly conductive features. Specifically, a series of bicontinuous PEMs are prepared by the controllable cross-linking of poly(ether-ether-ketone) and poly(4-vinylpyridine), followed by the inducement of phosphoric acid. These PEMs exhibit both a high proton conductivity of 70 mS cm^-1 and a high modulus of 39.3 MPa at 150 ℃, which can serve as high-performance electrolytes. The HT-SCs based on these PEMs display a specific capacitance of 138.0 F g^-1 and a high capacitance retention of 80.0% after 2500 galvanostatic charge-discharge cycles at 150 ℃, exhibiting excellent high-temperature capacitance and cycle stability. This post-assembly concept can provide a new route to design high-performance PEMs for HT-SC and other energy device applications.