Modern electrochemical energy conversion devices require more advanced proton conductors for their broad applications. Phosphonated polymers have been proposed as anhydrous proton conductors for fuel ...cells. However, the anhydride formation of phosphonic acid functional groups lowers proton conductivity and this prevents the use of phosphonated polymers in fuel cell applications. Here, we report a poly(2,3,5,6-tetrafluorostyrene-4-phosphonic acid) that does not undergo anhydride formation and thus maintains protonic conductivity above 200 °C. We use the phosphonated polymer in fuel cell electrodes with an ion-pair coordinated membrane in a membrane electrode assembly. This synergistically integrated fuel cell reached peak power densities of 1,130 mW cm
at 160 °C and 1,740 mW cm
at 240 °C under H
/O
conditions, substantially outperforming polybenzimidazole- and metal phosphate-based fuel cells. Our result indicates a pathway towards using phosphonated polymers in high-performance fuel cells under hot and dry operating conditions.
In this review the research of the author's group regarding the optimization of the chemical stability and properties of aromatic ion-exchange polymers by suitable and systematic synthesis of ...electron-deficient monomer building blocks and by their (co) polymerization into highly stable aromatic ionomers are presented. Moreover, the preparation of physically or covalently cross-linked ion-exchange membranes by blending these ionomers with each other and with suitable commercial polymers to finally afford ion-exchange membranes with properties tailored for electromembrane applications such as fuel cells, electrolyses, and redox-flow batteries are described.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Anion exchange blend membranes (AEBMs) were prepared for use in Vanadium Redox Flow Batteries (VRFBs). These AEBMs consisted of 3 polymer components. Firstly, PBI-OO (nonfluorinated PBI) or F6-PBI ...(partially fluorinated PBI) were used as a matrix polymer. The second polymer, a bromomethylated PPO, was quaternized with 1,2,4,5-tetramethylimidazole (TMIm) which provided the anion exchange sites. Thirdly, a partially fluorinated polyether or a non-fluorinated poly (ether sulfone) was used as an ionical cross-linker. While the AEBMs were prepared with different combinations of the blend polymers, the same weight ratios of the three components were used. The AEBMs showed similar membrane properties such as ion exchange capacity, dimensional stability and thermal stability. For the VRFB application, comparable or better energy efficiencies were obtained when using the AEBMs compared to the commercial membranes included in this study, that is, Nafion (cation exchange membrane) and FAP 450 (anion exchange membrane). One of the blend membranes showed no capacity decay during a charge-discharge cycles test for 550 cycles run at 40 mA/cm² indicating superior performance compared to the commercial membranes tested.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In order to evaluate the performance of the anion exchange membranes in a vanadium redox flow battery, a novel anion exchange polymer was synthesized via a three step process. Firstly, ...1-(2-dimethylaminoethyl)-5-mercaptotetrazole was grafted onto poly(pentafluorostyrene) by nucleophilic F/S exchange. Secondly, the tertiary amino groups were quaternized by using iodomethane to provide anion exchange sites. Finally, the synthesized polymer was blended with polybenzimidazole to be applied in vanadium redox flow battery. The blend membranes exhibited better single cell battery performance in terms of efficiencies, open circuit voltage test and charge-discharge cycling test than that of a Nafion 212 membrane. The battery performance results of synthesized blend membranes suggest that those novel anion exchange membranes are promising candidates for vanadium redox flow batteries.
Bipolar membrane|electrode interface water electrolyzers (BPEMWE) were found to outperform a proton exchange membrane (PEM) water electrolyzer reference in a similar membrane electrode assembly (MEA) ...design based on individual porous transport electrodes (PTE) and a free-standing membrane. We present a detailed study on bipolar interfaces between anion exchange ionomer (AEI) based anode catalyst layers in direct contact with a PEM aiming to unravel influences of local pH, the water splitting bipolar interface and catalyst layer structure. It is conventionally accepted that AEIs used in anion exchange- and bipolar membrane water electrolysis conduct hydroxide anions and ensure a high pH environment in the catalyst layer. We have investigated the effect of different ionomers on the local pH at a metal surface and found a strong correlation with the pH of the surrounding solution rather than the ionomer type. Thus, solely the use of an AEI cannot maintain high pH. A study on BPEMWEs revealed strong indications for the co-existence of a water dissociating bipolar interface, and an acidic oxygen evolution mechanism. The superior performance compared to a PTE-based PEM water electrolyzer seems to stem from reduced contact resistances due to adhesive effects between the oppositely charged polymers. Our study shows that the bipolar approach can be utilized to make PTE-based electrolyzers competitive to commonly employed catalyst coated membranes.
Bipolar interfaces located directly between a proton conducting membrane and an anion exchange ionomer based anode catalyst layer are investigated in membrane electrode assemblies for water electrolysis.
Both cation-exchange membranes and anion-exchange membranes are used as ion conducting membranes in vanadium redox flow batteries (VRFBs). Anion-exchange membranes (AEMs) are applied in vanadium ...redox flow batteries due to the high blocking property of vanadium ions via the Donnan exclusion effect. In this study, novel anion-exchange blend membranes (AEBMs) were prepared, characterized, and applied in VRFBs. Bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide), poly(1-(4,4′-diphenylether)-5-oxybenzimidazole)-benzimidazole (PBI-OO) and sulfonated polyether sulfone polymer were combined to prepare 3-component AEBMs with 1,2,4,5-tetramethylimidazole (TMIm) for quaternization. 3-component AEBMs showed significantly enhanced chemical and mechanical properties compared with those of 2-component AEBMs, resulting in an improved performance in VRFBs. The compositions of the anion-exchange polymers in 3-component AEBMs were systematically varied to optimize the AEBMs for the redox-flow battery application. While the 3-component AEBMs showed comparable efficiencies with Nafion
212 membranes, they displayed improved vanadium ions cross-over as was confirmed by open circuit voltage tests and capacity fade tests conducted in VRFBs. In addition, one of the synthesized 3-component AEBM had a superior coulombic efficiency and capacity retention in a charging⁻discharging test over 300 cycles at a current density of 40 mA/cm². It can thus be concluded that 3-component AEBMs are promising candidates for long-term operation in VRFBs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Novel morpholinium-functionalized anion-exchange blend membranes are presented in this study. The blended membranes consist of highly brominated poly(aryl ether) (PAE-Br) or ...poly(2,6-dimethyl-1,4-phenyleneoxide) (PPO-Br), partially fluorinated polybenzimidazole (F
6
-PBI) as the polymer matrix and/or a sulfonated polyethersulfone from 1,1′-biphenyl-4,4′-diol and potassium 5,5′-sulfonylbis(2-fluorobenzenesulfonate), abbreviated in this study as SAC. One of the manufactured blend membranes (IEC: 2.4 mmol g
−1
) had a better alkaline stability than the Tokuyama membrane A201. In addition, excellent thermal stability and moderate water uptake were observed for the blend. The enhanced thermophysical properties were ascribed to the PBI matrix, whereas the high bromination degree of the ionomer contributed to the high ion-exchange capacities and conductivities obtained. The significantly increased chemical stability noted for these blends can partially be attributed to supplementary ionic cross-links formed between acidic and basic components. These results, combined with the ability of PPO-Br and PAE-Br to form macroscopically homogeneous blends with PBIs, resulting in stable and flexible polymer films, reiterate the potential suitability of the presented membranes as polymer electrolytes for electrochemical applications such as alkaline fuel cells.
Ionic cross-linking between the SAC component and (a) F
6
PBI by imidazole group protonation or (b)
N
-methylmorpholine after quaternization.
In view of the many possible applications such as fuel cells and electrolysers, recent interest in novel anion exchange membranes (AEMs) has increased significantly. However, their low conductivity ...and chemical stability limits their current suitability. In this study, the synthesis and characterization of several three- and four-component anion exchange blend membranes (AEBMs) is described, where the compositions have been systematically varied to study the influence of the AEBM's composition on the anion conductivities as well as chemical and thermal stabilities under strongly alkaline conditions. It was shown that the epoxide-functionalized poly(ethylene glycol)s that were introduced into the four-component AEBMs resulted in increased conductivity as well as a marked improvement in the stability of the AEBMs in an alkaline environment. In addition, the thermal stability of the novel AEBMs was excellent showing the suitability of these membranes for several electrochemical applications.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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