Ion transport by nanochannels in ion-containing aromatic copolymers

The search for the next generation of highly ion-conducting polymer electrolyte membranes has been a subject of intense research because of their potential applications in energy storage and transformation devices, such as fuel cells, vanadium flow batteries, membrane-based artificial photosynthesis, water electrolysis, or water treatment processes such as electrodialysis desalination. Nanochannels that contain ionic groups, through which \u201chydrated\u201d ions can pass, are believed to be of key importance for efficient ion transport in polymer electrolytes membranes. In this Perspective, we present an overview of the approaches to induce ion-conducting nanochannel formation by self-assembly, using polymer architecture such as block or comb-shaped copolymers. The transport properties of ion-containing aromatic copolymers are examined to obtain an insight into the fundamental behavior of these materials, which are targeted toward applications in fuel cells and other electrochemical devices. Challenges in obtaining well-defined nanochannel morphologies, and possible strategies to improve transport properties in aromatic copolymers having structures with the potential to withstand operation in electrochemical/chemical devices, are discussed. Opportunities for the application of ion-containing aromatic copolymer membranes in fuel cells, vanadium flow batteries, membrane-based artificial photosynthesis, electrolysis, and electrodialysis are also reviewed. Research needs for further improvements in ionic conductivity and durability, and their applications are identified.Peer reviewed: YesNRC publication: Ye

Toward high conductivity in anion exchange membranes for alkaline fuel cells application

Quaternized poly(2,6-dimethylphenylene oxide) materials (PPOs) containing clicked 1,2,3-triazoles were first prepared through CuI-catalyzed \u201cclick chemistry\u201d to improve the anion transport in anion-exchange membranes (AEMs). Clicked 1,2,3-triazoles incorporated into AEMs provided more sites to form efficient and continuous hydrogen-bond networks between the water/hydroxide and the triazole for anion transport. Higher water uptake was observed for these triazole membranes. Thus, the membranes showed an impressive enhancement of the hydroxide diffusion coefficient and, therefore, the anion conductivities. The recorded hydroxide conductivity was 27.8\u201362\u2005mS\u2009cm 121 at 20\u2009\ub0C in water, which was several times higher than that of a typical PPO-based AEM (TMA-20) derived from trimethylamine (5\u2005mS\u2009cm 121). Even at reduced relative humidity, the clicked membrane showed superior conductivity to a trimethylamine-based membrane. Moreover, similar alkaline stabilities at 80\u2009\ub0C in 1\u2009M NaOH were observed for the clicked and non-clicked membranes. The performance of a H2/O2 single cell assembled with a clicked AEM was much improved compared to that of a non-clicked TMA-20 membrane. The peak power density achieved for an alkaline fuel cell with the synthesized membrane 1a(20) was 188.7\u2005mW\u2009cm 122 at 50\u2009\ub0C. These results indicated that clicked AEM could be a viable strategy for improving the performance of alkaline fuel cells.Peer reviewed: YesNRC publication: Ye

Controlled Functionalization Of Poly(4-Methyl-1-Pentene) Films For High Energy Storage Applications

A new family of poly(4-methyl-1-pentene) ionomer [PMP-(NH3)xA-y] (x = 1, 2, 3 and A = Cl-, SO42-, PO43-, y = NH3 content) modified (NH3+)xAx- ionic groups has been synthesized. The ionomers were synthesised using either a traditional Ziegler-Natta or a metallocene catalyst for the copolymerisation of 4-methyl-1-pentene and bis(trimethylsilyl)amino-1-hexene. A systematic study was conducted on the effect of the subsequent work-up procedures that can prevent undesirable side reactions during the synthesis of the [PMP-(NH3)xA-y] ionomers. The resulting PMP-based copolymers were carefully monitored by a combination of nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), mechanical properties, dielectric properties, and electric displacement-electric field (D-E) hysteresis loop measurements. Our results reveal that the [PMP-(NH3)xA-y] ionomer films show a significantly enhanced dielectric constant (∼5) and higher breakdown field (∼612 MV m-1) as compared with pure PMP films. Additionally, these PMP-based films show good frequency and temperature stabilities (up to 160 °C). A reliable energy storage capacity above 7 J cm-3 can be obtained, and is twice the energy storage capacity of state-of-the-art biaxially oriented polypropylene films, which can be attractive for technological applications for energy storage devices

Piperidinium-functionalized anion exchange membranes and their application in alkaline fuel cells and water electrolysis

To produce a stable anion exchange membrane (AEM) for deployable electrochemical devices with a long lifespan, we here present the synthesis and properties of a series of piperidinium-functionalized poly(2,6-dimethyl phenylene oxide)s with different locations of piperidinium groups along the polymer backbones. A distinct phase separated morphology was observed for long side-chain-type AEMs (LSCPi) as confirmed by AFM analysis, which in turn enabled its higher hydroxide conductivity over side-chain-type (SCPi) and standard benzylmethyl piperidinium AEMs (BPi). A hydroxide conductivity of 29.0 mScm(-1) at 20 degrees C was achieved for the LSCPi membrane with an IEC value of 1.57 meq. g(-1). This level of conductivity was lower than that of the corresponding QA-based AEMs (LSCQA) (38.7 mS cm(-1) at 20 degrees C), probably as a result of its low IEC accompanied by low water uptake. The LSCPi membrane displayed excellent alkaline stability with 98% retention in conductivity after 560 h of testing in 1 M NaOH at 80 degrees C, and no obvious degradation was detected by NMR analysis of the aged sample. To demonstrate the feasibility of piperidinium-functionalized AEMs, both SCPi and LSCPi membranes were fabricated into a membrane electrode assembly for the H-2/O-2 alkaline fuel cell and AEM water electrolyzer applications. The highly conductive LSCPi membrane showed good cell performance with a peak power density of 116 mW cm(-2) at 60 degrees C in alkaline fuel cells and 300 mA cm(-2) at 1.80 V at 50 degrees C in AEM water electrolysis working with pure water. Although a gradual drop in performance was observed for both the alkaline fuel cell and water electrolyser durability testing at a constant current during the test of 8.7 h and 35 h respectively, the high durability of AEMs having piperidinium cations was verified by post-mortem analysis of aged AEMs by NMR spectroscopy. The current findings provided fundamental insights into the durability of AEMs under ex situ and in situ operating conditions and demonstrated that the piperidinium-functionalized AEM appears to be a promising material for durable AEM-based devices

Highly Stable Anion Exchange Membranes Based On Quaternized Polypropylene

A series of novel quaternized polypropylene (PP) membranes with \u27side-chain-type\u27 architecture was prepared by heterogeneous Ziegler-Natta catalyst mediated polymerization and subsequent quaternization. Tough and flexible anion exchange membranes were prepared by melt-pressing of bromoalkyl-functionalized PP (PP-CH2Br) at 160°C, followed by post-functionalization with trimethylamine (TMA) or N,N-dimethyl-1-hexadecylamine (DMHDA) and ion exchange. By simple incorporation of a thermally crosslinkable styrenic diene monomer during polymerization, crosslinkable PP-AEMs were also prepared at 220°C. PP-AEM properties such as ion exchange capacity, thermal stability, water and methanol uptake, methanol permeability, hydroxide conductivity and alkaline stability of uncrosslinked and crosslinked membranes were investigated. Hydroxide conductivities of above 14 mS cm-1 were achieved at room temperature. The crosslinked membranes maintained their high hydroxide conductivities in spite of their extremely low water uptake (up to 56.5 mS cm-1 at 80°C, water uptake = 21.1 wt%). The unusually low water uptake and good hydroxide conductivity may be attributed to the side-chain-type structures of pendent cation groups, which probably facilitate ion transport. The membranes retained more than 85% of their high hydroxide conductivity in 5 M or 10 M NaOH aqueous solution at 80°C for 700 h, suggesting their excellent alkaline stability. It is assumed that the long alkyl spacer in the \u27side-chain-type\u27 of 9 carbon atoms between the polymer backbone and cation groups reduces the nucleophilic attack of water or hydroxide at the cationic centre. Thus, PP-based AEMs with long side-chain-type cations appear to be very promising candidates with good stability for use in anion exchange membrane fuel cells (AEMFCs)

Enhancement of H2 Separation Performance in Ring-Opened Tro?ger's Base Incorporating Modified MOFs

Energy-efficient hydrogen (H2) recovery technology is of great significance to developing H2-based economy and accomplishing global carbon-neutrality with minimized worldwide energy consumption. A ring-opened Tro''ger's base (TBOR) polymer membrane as a highly H2-selective membrane holds great promise for recovering H2 while partial microporosity loss induced by ring opening reaction deteriorates the H2 permeability across the pure membrane. Herein we introduce polydopamine-modified ZIF-8 (PDA-ZIF-8) nanoparticles into TBOR to develop a permeable membrane for selective H2 separation. The resultant mixed matrix membranes demonstrate the significantly improved H2 permeability, owing to the porous structure of ZIF-8, and efficiently exclude large molecules of CH4 and N2, giving rise to promising H2/CH4 and H2/N2 ideal selectivities. The PDA-ZIF-8 interacts with the secondary amines of TBOR via hydrogen bonds, creating good interfacial adhesion, thus preventing a sharp selectivity loss that occurred in most mixed matrix membranes upon increasing filler loadings. At a maximum ZIF-8 loading of 50 wt %, the pure H2 permeability is 457 Barrer, increasing to 4.2 times as compared with the undoped membrane, and the ideal H2/CH4 selectivity of 57 and ideal H2/N2 selectivity of 59 are achieved. The H2/CH4 separation properties remain unchanged upon increasing feed pressures, indicating the membrane's good stability when operated at realistic high pressures. The ring-opening functionalization of Tro''ger's base has proven to be very useful for fabricating selective mixed matrix membranes and can be extended for designing H2-selective hybrid membranes with other porous fillers

Polysulfones with Phenylalanine Derivatives as Chiral Selectors – Membranes for Chiral Separation

Polysulfone with a derivative of phenylalanyl residue as a chiral selector (PSf-Ac-D-Phe or PSf-Ac-L-Phe) were prepared by polymer reaction of benzylamine-modified polysulfones with N-a-acetyl-D-phenylalanine or N-a-acetyl-L-phenylalanine. Both polysulfones having a chiral selector gave durable self-standing membranes. The specific rotations of those polymers revealed that the chiral selectors were successfully introduced into the polysulfone. PSf-Ac-D-Phe membrane incorporated L-Glu in preference to D-Glu and vice versa. The chiral separation ability was studied by applying a concentration gradient as a driving force for membrane transport. Permselectivities for those two types of membrane reflected their adsorption selectivities. PSf-Ac-D-Phe membrane selectively transported L-Glu and vice versa. Predicted permselectivities by adopting membrane resistance coincided with the observed ones

Enhancement of H2 Separation Performance in Ring-Opened Tro?ger's Base Incorporating Modified MOFs

Energy-efficient hydrogen (H2) recovery technology is of great significance to developing H2-based economy and accomplishing global carbon-neutrality with minimized worldwide energy consumption. A ring-opened Tro''ger's base (TBOR) polymer membrane as a highly H2-selective membrane holds great promise for recovering H2 while partial microporosity loss induced by ring opening reaction deteriorates the H2 permeability across the pure membrane. Herein we introduce polydopamine-modified ZIF-8 (PDA-ZIF-8) nanoparticles into TBOR to develop a permeable membrane for selective H2 separation. The resultant mixed matrix membranes demonstrate the significantly improved H2 permeability, owing to the porous structure of ZIF-8, and efficiently exclude large molecules of CH4 and N2, giving rise to promising H2/CH4 and H2/N2 ideal selectivities. The PDA-ZIF-8 interacts with the secondary amines of TBOR via hydrogen bonds, creating good interfacial adhesion, thus preventing a sharp selectivity loss that occurred in most mixed matrix membranes upon increasing filler loadings. At a maximum ZIF-8 loading of 50 wt %, the pure H2 permeability is 457 Barrer, increasing to 4.2 times as compared with the undoped membrane, and the ideal H2/CH4 selectivity of 57 and ideal H2/N2 selectivity of 59 are achieved. The H2/CH4 separation properties remain unchanged upon increasing feed pressures, indicating the membrane's good stability when operated at realistic high pressures. The ring-opening functionalization of Tro''ger's base has proven to be very useful for fabricating selective mixed matrix membranes and can be extended for designing H2-selective hybrid membranes with other porous fillers