Synthesis and characterization of anion exchange blend membranes for vanadium redox flow battery applications

Due to the increasing concerns of fossil fuel using and environmental issues, the world needs to develop renewable energy sources and clean energy conversion devices, e.g. fuel cells, flow batteries and electrolyzers. Vanadium redox flow batteries (VRFBs) are considered promising energy storage system for large scale applications due to their long cycle lives, low cost, design flexibility and safety. Ion exchange membrane (IEM) is polymeric material composed of ionic head groups as fixed ions in polymeric backbone and transportable ions. Those types of membranes can be used in various applications which are energy related devices mentioned above. Therefore, developments of ion exchange membranes are required with improved properties to increase the efficiency of energy applications. Aim of this work is to develop ion exchange membranes with improved properties and to display better performances in VRFB compared to commercial reference membranes. Because currently available IEMs in VRFBs are limited due to fast vanadium ions cross-over or/and low ionic conductivity resulting in low performances in the battery. To overcome those drawbacks and to be used in vanadium redox flow battery, ion exchange membranes were developed either by blending or via new synthetic procedures. Thus, novel ion exchange polymers and/or membranes were developed, analyzed and applied in vanadium redox flow battery. In this dissertation, therefore, polymers synthesis, membranes preparation and applications of ion exchange membranes have been studied. This dissertation is divided into mainly three parts. The first part introduces a general background of the subject regarding ion conducting polymers and applications in vanadium redox flow battery. The second part is the papers published during the thesis work. The last part of this dissertation is overall discussion on the results and summary

Design and aberration study of a new miniature energy analyzer with correctors in a scanning electron microscope

The authors design a new miniature energy analyzer with a magnetic sector and corrector systems that can be installed in a scanning electron microscope for measurement of electron energy loss spectra. In order to correct the geometrical aberration caused by a magnetic sector field, two new corrector systems are designed using ray tracing simulations. One corrector system, using a simple structure, fully corrects second-order aberration and partially corrects third-order aberration. Another corrector system fully corrects third-order aberration in the x-direction. By aberration correction, energy resolution of similar to 10 meV at an initial angle of 5 mrad can be achieved with either of the two corrector systems. Additionally, we reveal an overall process of aberration correction in ray tracing simulations, which can be a useful guideline for aberration correction. Notably, we have established a new method of aberration correction using a simple matrix equation. Using this method, second-order aberration can be fully corrected both conveniently and rapidly. This study enables us to easily calculate and correct geometrical aberration without solving complicated equations.11Nsciescopu

Performances of Anion-Exchange Blend Membranes on Vanadium Redox Flow Batteries

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

Novel Anion Exchange Membrane Based on Poly(Pentafluorostyrene) Substituted with Mercaptotetrazole Pendant Groups and Its Blend with Polybenzimidazole for Vanadium Redox Flow Battery Applications

In order to evaluate the performance of the anion exchange membranes in a vanadiumredox 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 usingiodomethane to provide anion exchange sites. Finally, the synthesized polymer was blended withpolybenzimidazole to be applied in vanadium redox flow battery. The blend membranes exhibitedbetter single cell battery performance in terms of efficiencies, open circuit voltage test and chargedischargecycling test than that of a Nafion 212 membrane. The battery performance results ofsynthesized blend membranes suggest that those novel anion exchange membranes are promisingcandidates for vanadium redox flow batteries

Application of Novel Anion-Exchange Blend Membranes (AEBMs) to Vanadium Redox Flow Batteries

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

Electrospun sulfonated poly(ether ketone) nanofibers as proton conductive reinforcement for durable Nafion composite membranes

We show that the combination of direct membrane deposition with proton conductive nanofiber reinforcement yields highly durable and high power density fuel cells. Sulfonated poly(ether ketone) (SPEK) was directly electrospun onto gas diffusion electrodes and then filled with Nafion by inkjet-printing resulting in a 12 μm thin membrane. The ionic membrane resistance (30 mΩ*cm2) was well below that of a directly deposited membrane reinforced with chemically inert (PVDF-HFP) nanofibers (47 mΩ*cm2) of comparable thickness. The power density of the fuel cell with SPEK reinforced membrane (2.04 W/cm2) is 30% higher than that of the PVDF-HFP reinforced reference sample (1.57 W/cm2). During humidity cycling and open circuit voltage (OCV) hold, the SPEK reinforced Nafion membrane showed no measurable degradation in terms of H2 crossover current density, thus fulfilling the target of 2 mA/cm2 of the DOE after degradation. The chemical accelerated stress test (100 h OCV hold at 90 °C, 30% RH, H2/air, 50/50 kPa) revealed a degradation rate of about 0.8 mV/h for the fuel cell with SPEK reinforced membrane, compared to 1.0 mV/h for the PVDF-HFP reinforced membrane

Simple fabrication of 12 μm thin nanocomposite fuel cell membranes by direct electrospinning and printing

Direct membrane deposition (DMD) was recently introduced as a novel polymer electrolyte membrane fabrication method. Here, this approach is extended to fabricate 12 μm thin nanocomposite fuel cell membranes. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers are directly electrospun onto gas diffusion electrodes. By inkjet-printing Nafion ionomer dispersion into the pore space of PVDF-HFP nanofiber mats, composite membranes of 12 μm thickness were fabricated. At 120 °C and 35% relative humidity, stoichiometric 1.5/2.5 H2/air flow and atmospheric pressure, the power density of the DMD fuel cell (0.19 W cm-2), was about 1.7 times higher than that of the reference fuel cell (0.11 W cm-2) with Nafion HP membrane and identical catalyst. A lower ionic resistance and, especially at 120 °C, a reduced charge transfer resistance is found compared to the Nafion HP membrane. A 100 h accelerated stress test revealed a voltage decay of below 0.8 mV h-1, which is in the range of literature values for significantly thicker reinforced membranes. Finally, this novel fabrication approach enables new degrees of freedom in the design of complex composite membranes. The presented combination of scalable deposition techniques has the potential to simplify and thus reduce cost of composite membrane fabrication at a larger scale

Sulfonated Copper Phthalocyanine/Sulfonated Polysulfone Composite Membrane for Ionic Polymer Actuators with High Power Density and Fast Response Time

Ionic polymer composite membranes based on sulfonated poly­(arylene ether sulfone) (SPAES) and copper­(II) phthalocyanine tetrasulfonic acid (CuPCSA) are assembled into bending ionic polymer actuators. CuPCSA is an organic filler with very high sulfonation degree (IEC = 4.5 mmol H⁺/g) that can be homogeneously dispersed on the molecular scale into the SPAES membrane, probably due to its good dispersibility in SPAES-containing solutions. SPAES/CuPCSA actuators exhibit larger ion conductivity (102 mS cm^–1), tensile modulus (208 MPa), strength (101 MPa), and strain (1.21%), exceptionally faster response to electrical stimuli, and larger mechanical power density (3028 W m^–3) than ever reported for ion-conducting polymer actuators. This outstanding actuation performance of SPAES/CuPCSA composite membrane actuators makes them attractive for next-generation transducers with high power density, which are currently developed, e.g., for underwater propulsion and endoscopic surgery