Academic literature on the topic 'PBI blend membranes'

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.

Alternative energy sources are needed if the current use of energy is to be sustained while reducing global warming. A possible alternative energy source that has significant potential is hydrogen. For hydrogen to become a serious contender for replacing fossil fuels, the production thereof has to be further investigated. One such process, the membrane–based Hybrid Sulphur (HyS) process, where hydrogen is produced from the electrolysis of SO2, has received considerable interest recently. Since H2SO4 is formed during SO2 electrolysis, H2SO4 stability is a prerequisite for any membrane to be used in this process. In this study, pure as well as high and low temperature blended polybenzimidazole (PBI), partially fluorinated poly(arylene ether) (sFS) and nonfluorinated poly(arylene ethersulphone) (sPSU) membranes were investigated in terms of their acid stability as a function of acid concentration by treating them in H2SO4 (30, 60 and 90wt%) for 120h at 1bar pressure. The high temperature blend membranes contain the basic polymer in excess (70 wt% basic PBI and 30wt% acid sPSU/sFS polymer) and require acid doping in order to conduct protons. In the doped state they are able to conduct protons up to 200°C. The low temperature blend membranes are also composed of the same PBI polymer used in the high temperature membranes, as well as the same acidic polymers with one of the membranes containing a fluorinated polymer and the other a nonfluorinated polymer (sFS or sPSU) in excess. These membranes do not require any acid doping to conduct protons but they are only stable at temperatures below 80°C. High temperature blend membranes were characterised using through–plane conductivity, GPC and IEC, whilst low temperature membranes were characterised using in–plane and through–plane proton conductivity, weight change, TGA, GPC, SEM, EDX and IEC techniques. The conductivity determination techniques (especially the in–plane technique) proved to be cumbersome, whilst all the other analysis techniques were deemed appropriate. H2SO4 exposure had a destabilising effect on the PBI membrane which presented as weight gain at the 30 and 60wt% H2SO4 concentrations due to salt formation and dissolution at the 90wt% acid treatment due to sulphonation. In the sFS membrane dissolution was observed at 30 and 60wt% as a result of oligomer loss that occurred during the post treatment washing process and partial dissolution, as a result of sulphonation, at the 90wt% treated membrane. The sPSU membrane showed great stability at 30 and 60wt%, though dissolution was observed at 90wt% because of membrane sulphonation due to a lack of fluorination. The sFS–PBI membrane blend proved to be stable with only slight degradation taking place at 90wt% treatment due to sulphonation. Similarly the sPSU–PBI blend membrane showed great stability at the 30 and 60wt% H2SO4 treatment concentrations however total dissolution occurred at 90wt% treatment again due to a lack of fluorination. Although both the low temperature blended membranes showed superb stability to H2SO4 concentrations expected in the SO2 electrolyser (30–40wt%), the low temperature blended sFS–PBI membrane seemed slightly more stable over the H2SO4 treatment concentration range (30–90wt%), due to the protective role of the fluorinated polymer. The superior acid stability of this membrane could prove vital for proper SO2 electrolysis, especially for prolonged periods of operation
Thesis (M.Sc. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2012.

碩士
元智大學
化學工程與材料科學學系
97
In this thesis, we synthesized polybenzimidazole (PBI) and its derivative butyl sulfonated poly(polybenzimidazole) (PBI-BS). PBI/PBI-BS blend membranes were prepared with a PBI/PBI-BS wt ratio of 8/2. The chemical structure and physical properties of the membrane were investigated, using FTIR, SEM, EDS, and TGA. 400 h continuous stability life test and 298 h start/stop cycle test (10 h/start – 14 h/stop) on the MEA prepared from phosphoric acid-doped PBI/PBI-BS were conducted at 160℃with a current density= 200 mAcm−2. i-V polarization curve and AC-impedance test of MEA were performed every 12 h in the long time life test and each cycle in the start/stop cycle test. The data of 400 h life test showed decay of cell voltage V around 17% and the increments of resistance of membrane and electrolyte with increasing test time. The low pH value of the water collected from cathode outlet migration of H3PO4 from MEA. The 298 h start/stop cycle test showed no significant change of cell voltage V and membrane resistance, but increment of charge transfer of catalyst layer. The low pH value of water was also collected from cathode outlet during the start/stop cycle test. This result also indicates migration of H3PO4 during start/stop cycle test.

The environmentally unsafe by-products (CO2, H2S, NOx and SO2 for example) of using carbon-based fuels for energy generation have paved the way for research on cleaner, renewable and possibly cheaper alternative energy production methods. Hydrogen gas, which is considered as an energy carrier, can be applied in a fuel cell setup for the production of electrical energy. Although various methods of hydrogen production are available, sulphur-based thermochemical processes (such as the Hybrid Sulfur Process (HyS)) are favoured as alternative options for large scale application. The SO2 electrolyser is applied in producing H2 gas and H2SO4 by electrochemically converting SO2 gas and water. This study focused firstly on the evaluation of the performance of the SO2 electrolyser for the production of hydrogen and sulphuric acid, using commercially available PFSA (perfluorosulfonic acid) (Nafion®) as benchmark by evaluating i) various operating parameters (such as cell temperature and membrane thickness), ii) the influence of MEA (membrane electrode assembly) manufacturing parameters (hot pressing time and pressure) and iii) the effect of H2S as a contaminant. Subsequently, the suitability of novel PBI polyaromatic blend membranes was evaluated for application in an SO2 electrolyser. The parametric study revealed that, depending on the desired operating voltage and acid concentration, the optimisation of the operating conditions was critical. An increased cell temperature promoted both cell voltage and acid concentration while the use of thin membranes resulted in a reduced voltage and acid concentration. While an increased catalyst loading resulted in increased cell efficiency, such increase would result in an increase in manufacturing costs. Using electrochemical impedance spectroscopy at the optimised operating conditions, the MEA manufacturing process was optimised with respect to hot press pressure and time, while the effect of selected operating conditions was used to evaluate the charge transfer resistance, ohmic resistance and mass transport limitations. Results showed that the optimal hot pressing conditions were 125 kg.cm-2 and 50 kg.cm-2 for 5 minutes when using 25 and 10 cm2 active areas, respectively. The charge transfer resistance and mass transport were mostly influenced by the hot pressing procedure, while the ohmic resistance varied most with temperature. Applying the SO2 electrolyser in an alternative environment to the HyS thermochemical cycle, the effect of H2S on the SO2 electrolyser anode was investigated for the possible use of SO2 electrolysis to remove SO2 from mining off-gas which could contain H2S. Polarisation curves, EIS and CO stripping were used to evaluate the transient voltage response of various H2S levels (ppm) on cell efficiency. EIS confirmed that the charge transfer resistance increased as the H2S competed with the SO2 for active catalyst sites. Mass transport limitations were observed at high H2S levels (80 ppm) while the ECSA (electrochemical surface area obtained by CO stripping) showed a significant reduction of active catalyst sites due to the presence of H2S. Pure SO2 reduced the effective active area by 89% (which is desired in this case) while the presence of 80 ppm H2S reduced the active catalyst area to 85%. The suitability of PBI-based blend membranes in the SO2 electrolyser was evaluated by using chemical stability tests and electrochemical MEA characterisation. F6PBI was used as the PBI-containing base excess polymer which was blended with either partially fluorinated aromatic polyether (sFS001), poly(2,6-dimethylbromide-1,4-phenylene oxide (PPOBr) or poly(tetrafluorostyrene-4-phosphonic acid) (PWN) in various ratios. Some of the blend membranes also contained a cross-linking agent which was specifically added in an attempt to reduce swelling and promote cross-linking within the polymer matrix. The chemical stability of the blended membranes was confirmed by using weight and swelling changes, TGA-FTIR and TGA-MS. All membranes tested showed low to no chemical degradation when exposed to 80 wt% H2SO4 at 80°C for 120 h. Once the MEA doping procedure had been optimised, electrochemical characterisation of the PBI MEAs, including polarisation curves, voltage stepping and long term operation (> 24 h) was used to evaluate the MEAs. Although performance degradation was observed for the PBI membranes during voltage stepping, it was shown that this characterisation technique could be applied with relative ease, producing valuable insights into MEA stability. Since it is expected that the SO2 electrolyser will be operated under static conditions (cell temperature, pressure and current density) in an industrial setting (HyS cycle or for SO2 removal), a long term study was included. Operating the SO2 electrolyser under constant current density of 0.1 A cm-2 confirmed that PBI-based polyaromatic membranes were suitable, if not preferred, for the SO2 environment, showing stable performance for 170 hours. This work evaluated the performance of commercial materials while further adding insights into both characterisation techniques for chemical stability of polymer materials and electrochemical methods for MEA evaluation to current published literature. In addition to the characterisation techniques this study also provides ample support for the use of PBI-based materials in the SO2 electrolyser.
PhD (Chemistry), North-West University, Potchefstroom Campus, 2015

Phosphoric acid doped poly(benzimidazole) (PBI) is one of excellent candidates of proton exchange membranes for high temperature (150–180°C) proton exchange membrane fuel cells (PEMFCs). However, the strong inter-polymer hydrogen bonds cause low elongation and brittleness of PBI membranes. In this work, we synthesize poly(benzimidazole) (PBI) and butylsulfonated poly(benzimidazole) (PBI-BS), in which around 22 mole% of imidazole –NH groups of PBI are grafted with sulfonated butyl groups. We show the elongation, phosphoric acid doping level, and proton conductivity of PBI can be improved by blending ∼ 20 wt% of PBI-BS in the PBI membrane, and the membrane electrode assembly prepared from PBI/PBI-BS (8/2 by wt) blend membrane has a better PEMFC performance at 140°C ∼ 180°C than that prepared from PBI membrane. It is believed that the crosslink interactions of imidazole -NH and -N=C-groups with side chain –C4H8−SO3H groups of PBI-BS reduces the inter-PBI hydrogen bonds and increases the free volume of polymers, which leads to the enhancements of the membrane toughness and phosphoric acid doping level and the PEMFC performance.