Phenolphthalein-based Poly(arylene ether sulfone nitrile)s Multiblock Copolymers As Anion Exchange Membranes for Alkaline Fuel Cells

Novel Fluorinated Anion Exchange Membranes Based on Poly(Pentafluorophenyl-Carbazole) with High Ionic Conductivity and Alkaline Stability for Fuel Cell Applications

Constructing good microphase separation structures by designing different polymer backbones and ion-conducting groups is an effective strategy for improving the ionic conductivity and chemical stability of anion exchange membranes (AEMs). In this study, a series of AEMs based on the poly(pentafluorophenylcarbazole) backbone grafted with different cationic groups are designed and prepared to construct well-defined microphase separation morphology and improve the trade-off between the properties of AEMs. Highly hydrophobic fluorinated backbone and alkyl spaces enhance phase separation and construct interconnected hydrophilic channels for anion transport. The ionic conductivity of the PC-PF-QA membrane is 123 mS cm-1 at 80 °C, and the ionic conductivity of the PC-PF-QA membrane decreased by only 6% after 960 h of immersion at 60 °C in 1 M NaOH aqueous solution. The maximum peak power density of the single cell based on PC-PF-QA is 214 mW cm-2 at 60 °C.

Phthalide cardo chain extended imine skeletal linked maleimido end capped nanotitania reinforced novel polybenzoxazine (nTiO2/PBZ) hybrid nanocomposites

A new class of nanotitania reinforced polybenzoxazine (nTiO2/PBZ) hybrid nanocomposites was synthesized using newly designed phthalide cardo chain extended imine skeletal linked maleimido end capped polybenzoxazine (PHM-PBZ) and nTiO2 through in-situ sol-gel method. The formation of hybrid nanocomposites was confirmed by NMR and FT-IR spectra. The structurally stable nTiO2 present in the nTiO2/PBZ hybrids accounted their exceptional thermal stability and good char yield. The restricted motion of flexible polymeric chain resulted from the inclusion of nTiO2 in the PBZ system increased the glass transition temperature ( T g) to a higher percentage than that of neat PBZ system. With the successive enhancement in the incorporation of nTiO2, the synthesized nanocomposites exhibited better thermal stability, higher flame retardancy and lesser water absorption behaviour than the of neat PBZ. The sequential increments in the loading level of nTiO2 onto the PBZ matrices caused the lower value of dielectric constant than that of neat PBZ. The homogeneity and successful dispersion of the nTiO2 fillers in the PBZ matrix were ascertained from the strong fluorescent emissions observed in the wavelength range of 300–550 nm through optical studies. Scanning electron microscope and transmission electron microscopic micrographs evidenced the successful incorporation of nTiO2 as can be seen from the different morphology at the nanoscale level in the PBZ matrix. This kind of structurally designed nTiO2/PBZ nanocomposites may find multifaceted applications in the form of adhesives, encapsulants, matrices and sealants and in the fields of automobile and microelectronics applications for better performance and longevity.

Phenolphthalein Anilide Based Poly(Ether Sulfone) Block Copolymers Containing Quaternary Ammonium and Imidazolium Cations: Anion Exchange Membrane Materials for Microbial Fuel Cell

A class of phenolphthalein anilide (PA)-based poly(ether sulfone) multiblock copolymers containing pendant quaternary ammonium (QA) and imidazolium (IM) groups were synthesized and evaluated as anion exchange membrane (AEM) materials. The AEMs were flexible and mechanically strong with good thermal stability. The ionomeric multiblock copolymer AEMs exhibited well-defined hydrophobic/hydrophilic phase-separated morphology in small-angle X-ray scattering and atomic force microscopy. The distinct nanophase separated membrane morphology in the AEMs resulted in higher conductivity (IECw = 1.3-1.5 mequiv./g, σ(OH^-) = 30-38 mS/cm at 20 °C), lower water uptake and swelling. Finally, the membranes were compared in terms of microbial fuel cell performances with the commercial cation and anion exchange membranes. The membranes showed a maximum power density of ~310 mW/m² (at 0.82 A/m²); 1.7 and 2.8 times higher than the Nafion 117 and FAB-PK-130 membranes, respectively. These results demonstrated that the synthesized AEMs were superior to Nafion 117 and FAB-PK-130 membranes.

A highly stable aliphatic backbone from visible light-induced RAFT polymerization for anion exchange membranes

A novel strategy that exploits “visible light-induced RAFT” is presented for fabricating alkaline stable AEMs with fully aliphatic backbones.

Poly(meta/para-Terphenylene-Methyl Piperidinium)-Based Anion Exchange Membranes: The Effect of Backbone Structure in AEMFC Application

A series of poly(meta/para-terphenylene-methyl piperidinium)-based anion exchange membranes devoid of benzylic sites or aryl ether bonds, that are vulnerable to degradation by hydroxide ions, are synthesized and investigated for their application as novel anion exchange membranes. The copolymers are composed of both linear para-terphenyl units and kink-structured meta-terphenyl units. The meta-connectivity in terphenyl units permits the polymer backbones to fold back, maximizing the interactions among the hydrocarbon polymer chains and enhancing the peripheral formation of ion aggregates, due to the free volume generated by the kink structure. The effects of the copolymer composition between para-terphenyl and meta-terphenyl on the morphology and the electrochemical and physicochemical properties of the corresponding polymer membranes are investigated.

Nanofiber Based Organic Solvent Anion Exchange Membranes for Selective Separation of Monovalent anions

Present anion exchange membranes are generally constructed by simple and positively charged polymers with insufficient organic solvent resistance, and exhibit a low selectivity in the separation of anions. Here, dissolving poly(paraphenylene terephthalamide) nanofibers into small nanofibers and performing a reaction with quaternary ammonium groups in the one-dimensional small nanofibers, high-performance anion exchange membranes were successfully fabricated. By increasing the 2,3-epoxypropyl trimethylammonium chloride content, the synthesized amide nanofiber quaternary ammonium membranes (ANF#QA) exhibited a higher anion exchange capacity (as high as 1.75 mmol·g^-1) and achieved a high electrochemical performance. In electrodialysis, the ANF#QA-10 membrane showed an exceptional Cl^- selectivity in dilute and concentrated cells. Due to the dense structure and presence of carboxyl groups on the nanofibers, the ANF#QA membranes exhibited a selective separation of monovalent anions. After 48 h of immersion in aqueous acetone solutions, the final ANF#QA-10 membrane exhibited high desalination and concentration efficiency as the initial membrane. This work highlights the promising use of positive charges on small nanofibers, and proposes the design of a special anion exchange membrane, which can be used for electrodialysis in organic solvent solutions, and to selectively separate monovalent anions.

Anion Exchange Membranes Obtained from Poly(arylene ether sulfone) Block Copolymers Comprising Hydrophilic and Hydrophobic Segments

The anion exchange membrane may have different physical and chemical properties, electrochemical performance and mechanical stability depending upon the monomer structure, hydrophilicity and hydrophobic repeating unit, surface form and degree of substitution of functional groups. In current work, poly(arylene ether sulfone) (PAES) block copolymer was created and used as the main chain. After controlling the amount of NBS, the degree of bromination (DB) was changed in Br-PAES. Following that, quaternized PAES (Q-PAES) was synthesized through quaternization. Q-PAES showed a tendency of enhancing water content, expansion rate, ion exchange capacity (IEC) as the degree of substitution of functional groups increased. However, it was confirmed that tensile strength and dimensional properties of membrane reduced while swelling degree was increased. In addition, phase separation of membrane was identified by atomic force microscope (AFM) image, while ionic conductivity is greatly affected by phase separation. The Q-PAES membrane demonstrated a reasonable power output of around 64 mW/cm² while employed as electrolyte in fuel cell operation.

Comb-shaped cardo poly(arylene ether nitrile sulfone) anion exchange membranes: significant impact of nitrile group content on morphology and properties

A series of comb-shaped cardo poly(arylene ether nitrile sulfone) (CCPENS-x) materials were synthesized by varying the content of nitrile groups as anion exchange membranes (AEMs). The well-designed architecture of cardo-based main chains and comb-shaped C10 long alkyl side chains bearing imidazolium groups was responsible for the clear microphase-separated morphologies, as confirmed by atomic force microscopy. The ion exchange capacity (IEC) of the AEMs ranged from 1.56 to 1.65 meq. g⁻¹. With strong dipole interchain interactions, the effects of nitrile groups on the membrane morphology and properties were investigated. With the nitrile group content increasing from CCPENS-0.2 to CCPENS-0.8, CCPENS-x revealed larger and more interconnected ionic domains to form more efficient ion-transport channels, thus increasing the corresponding ionic conductivity from 25.8 to 39.5 mS cm⁻¹ at 30 °C and 58.6 to 83 mS cm⁻¹ at 80 °C. Furthermore, CCPENS-x with a higher content of nitrile groups also exhibited lower water uptake (WU) and swelling ratio (SR), and better mechanical properties and thermal stability. This work presents a promising strategy for enhancing the performance of AEMs.

A series of comb-shaped cardo poly(arylene ether nitrile sulfone) (CCPENS-x) materials were synthesized by varying the content of nitrile groups as anion exchange membranes (AEMs).

Highly Conductive and Water-Swelling Resistant Anion Exchange Membrane for Alkaline Fuel Cells

To ameliorate the trade-off effect between ionic conductivity and water swelling of anion exchange membranes (AEMs), a crosslinked, hyperbranched membrane (C-HBM) combining the advantages of densely functionalization architecture and crosslinking structure was fabricated by the quaternization of the hyperbranched poly(4-vinylbenzyl chloride) (HB-PVBC) with a multiamine oligomer poly(N,N-Dimethylbenzylamine). The membrane displayed well-developed microphase separation morphology, as confirmed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Moreover, the corresponding high ionic conductivity, strongly depressed water swelling, high thermal stability, and acceptable alkaline stability were achieved. Of special note is the much higher ratio of hydroxide conductivity to water swelling (33.0) than that of most published side-chain type, block, and densely functionalized AEMs, implying its higher potential for application in fuel cells.

Promoter Effects of Functional Groups of Hydroxide-Conductive Membranes on Advanced CO2 Electroreduction to Formate

The electrochemical reduction of CO₂ at ambient conditions provides a latent solution of turning waste greenhouse gases into commodity chemicals or fuels; however, a satisfactory ion-conducting membrane for maximizing the performance of a CO₂ electrolyzer has not been developed. Here, we report the synthesis of a sequence of hydroxide-conductive polymer membranes, which are based on polymer composites of poly(vinyl alcohol)/Guar hydroxypropyltrimonium chloride, for use in CO₂ electrolysis. The effect of different membrane functional groups, including thiophene, hydroxybenzyl, and dimethyloctanal, on the efficiency and selectivity of CO₂ electroreduction to formate is thoroughly evaluated. The membrane incorporating thiophene groups exhibits the highest Faradaic efficiency of 71.5% at an applied potential of -1.64 V versus saturated calomel electrode (SCE) for formate. In comparison, membranes containing hydroxybenzyl and dimethyloctanal groups produced lower efficiencies of 67.6 and 68.6%, respectively, whereas the commercial Nafion 212 membrane was only 57.6% efficient. The improved efficiency and selectivity of membranes containing thiophene groups are attributed to a significantly increased hydroxide conductivity (0.105 S cm^-1), excellent physicochemical properties, and the simultaneous attenuation of formate product crossover.

Improved Physicochemical Stability and High Ion Transportation of Poly(Arylene Ether Sulfone) Blocks Containing a Fluorinated Hydrophobic Part for Anion Exchange Membrane Applications

A series of anion exchange membranes composed of partially fluorinated poly(arylene ether sulfone)s (PAESs) multiblock copolymers bearing quaternary ammonium groups were synthesized with controlled lengths of the hydrophilic precursor and hydrophobic oligomer via direct polycondensation. The chloromethylation and quaternization proceeded well by optimizing the reaction conditions to improve hydroxide conductivity and physical stability, and the fabricated membranes were very flexible and transparent. Atomic force microscope images of quaternized PAES (QN-PAES) membranes showed excellent hydrophilic/hydrophobic phase separation and distinct ion transition channels. An extended architecture of phase separation was observed by increasing the hydrophilic oligomer length, which resulted in significant improvements in the water uptake, ion exchange capacity, and hydroxide conductivity. Furthermore, the open circuit voltage (OCV) of QN-PAES X10Y23 and X10Y13 was found to be above 0.9 V, and the maximum power density of QN-PAES X10Y13 was 131.7 mW cm-2 at 60 °C under 100% RH.

Alkaline Exchange Polymer Membrane Electrolyte for High Performance of All-Solid-State Electrochemical Devices

As a potential solution to ubiquitous energy concerns, anion-exchange membranes (AEMs) have been widely used as the electrolyte in alkaline fuel cells (AFCs), and significant refinement of AEMs has been achieved in the past few decades. However, it remains unknown whether AEMs can be used as an electrolyte in a solid-state supercapacitor or zinc-air battery. A low-cost alkaline exchange membrane electrolyte composed of chitosan and poly(diallyldimethylammonium chloride) that possesses a high OH^- conductivity (0.024 S cm^-1), strong alkaline stability (216 h at 8 M KOH), good thermal stability, and low degree of anisotropic swelling, was found to provide a high electrochemical performance in all-solid-state devices. Prototypes of the solid AFC with the membrane shows superior stability over 500 h. The carbon nanotube-based all-solid-state supercapacitor with the membrane generated a rectangular cyclic voltammetry curve up to 10 V s^-1 and excellent cycling stability of 4000 cycles with 84% specific capacitance retention. The all-solid-state zinc-air battery demonstrates high power density (48.9 mW cm^-2). These advantages indicate that the membrane is a promising electrolyte for all-solid-state electrochemical devices.

Block poly(arylene ether sulfone) copolymers tethering aromatic side-chain quaternary ammonium as anion exchange membranes

A series of poly(arylene ether sulfone) block copolymer ionomers have been synthesized with different hydrophobic and hydrophilic segments, where benzyl-quaternary ammonium groups are tethered to the side chains of hydrophilic blocks.

Highly Hydroxide-Conductive Nanostructured Solid Electrolyte via Predesigned Ionic Nanoaggregates

The creation of interconnected ionic nanoaggregates within solid electrolytes is a crucial yet challenging task for fabricating high-performance alkaline fuel cells. Herein, we present a facile and generic approach to embedding ionic nanoaggregates via predesigned hybrid core-shell nanoarchitecture within nonionic polymer membranes as follows: (i) synthesizing core-shell nanoparticles composed of SiO₂/densely quaternary ammonium-functionalized polystyrene. Because of the spatial confinement effect of the SiO₂ "core", the abundant hydroxide-conducting groups are locally aggregated in the functionalized polystyrene "shell", forming ionic nanoaggregates bearing intrinsic continuous ion channels; (ii) embedding these ionic nanoaggregates (20-70 wt %) into the polysulfone matrix to construct interconnected hydroxide-conducting channels. The chemical composition, physical morphology, amount, and distribution of the ionic nanoaggregates are facilely regulated, leading to highly connected ion channels with high effective ion mobility comparable to that of the state-of-the-art Nafion. The resulting membranes display strikingly high hydroxide conductivity (188.1 mS cm^-1 at 80 °C), which is one of the highest results to date. The membranes also exhibit good mechanical properties. The independent manipulation of the conduction function and nonconduction function by the ionic nanoaggregates and nonionic polymer matrix, respectively, opens a new avenue, free of microphase separation, for designing high-performance solid electrolytes for diverse application realms.