Water uptake and acid doping of polybenzimidazoles as electrolyte membranes for fuel cells

Li, Qingfeng; He, Ronghuan; Berg, Rolf W.; Hjuler, Hans Aage; Bjerrum, Niels

doi:10.1016/j.ssi.2004.02.013

Cited by 333 publications

(236 citation statements)

References 32 publications

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“…The infrared (IR) [30,31,[181][182][183][184][185][186][187][188], Raman spectroscopy [187][188][189] and nuclear magnetic resonance (NMR) spectra [181,182,186] have been made to investigate the polymer and its protonation by acids. For pristine PBI, the IR spectrum [183][184][185] from 2000 to 4000 cm −1 is of particular interest since most of the informative N-H stretching modes occur in this range, with typically three distinguishable bands at 3415, 3145 and 3063 cm −1 .…”

Section: Spectroscopic Studiesmentioning

confidence: 99%

High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

Jensen

Savinell

et al. 2009

Progress in Polymer Science

1,243

852

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. To achieve high temperature operation of proton exchange membrane fuel cells (PEMFC), preferably under ambient pressure, acid-base polymer membranes represent an effective approach. The phosphoric acid-doped polybenzimidazole membrane seems so far the most successful system in the field. It has in recent years motivated extensive research activities with great progress. This treatise is devoted to updating the development, covering polymer synthesis, membrane casting, physicochemical characterizations and fuel cell technologies. To optimize the membrane properties, high molecular weight polymers with synthetically modified or N-substituted structures have been synthesized. Techniques for membrane casting from organic solutions and directly from acid solutions have been developed. Ionic and covalent cross-linking as well as inorganic-organic composites has been explored. Membrane characterizations have been made including spectroscopy, water uptake and acid doping, thermal and oxidative stability, conductivity, electro-osmotic water drag, methanol crossover, solubility and permeability of gases, and oxygen reduction kinetics. Related fuel cell technologies such as electrode and MEA fabrication have been developed and high temperature PEMFC has been successfully demonstrated at temperatures of up to 200• C under ambient pressure. No gas humidification is mandatory, which enables the elimination of the complicated humidification system, compared with Nafion cells. Other operating features of the PBI cell include easy control of air flow rate, cell temperature and cooling. The PBI cell operating at above 150• C can tolerate up to 1% CO and 10 ppm SO 2 in the fuel stream, allowing for simplification of the fuel processing system and possible integration of the fuel cell stack with fuel processing units. Long-term durability with a degradation rate of 5 V h −1 has been achieved under continuous operation with hydrogen and air at 150-160• C. With load or thermal cycling, a performance loss of 300 V per cycle or 40 V h −1 per operating hour was observed. Further improvement should be done by, e.g. optimizing the thermal and chemical stability of the polymer, acid-base interaction and acid management, activity and stability of catalyst and more importantly the catalyst support, as well as the integral interface between electrode and membrane.

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Section: Spectroscopic Studiesmentioning

confidence: 99%

High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

Jensen

Savinell

et al. 2009

Progress in Polymer Science

1,243

852

View full text Add to dashboard Cite

show abstract

“…2 PA molecules per PBI repeating unit (PA/PBI) are directly interacting with the basic pyridinic nitrogen of PBI. 5 However, PA doping levels are typically significantly higher, e.g., 5-10 for PA imbibed PBI films 6 and 20-40 for PBI membranes produced through the so-called poly-phosphoric acid (PPA) process. 7 It can, therefore, be expected that the bulk of this phosphoric acid is more or less mobile within the molecular pores of the membrane.…”

Section: High Temperature Polymer Electrolyte Fuel Cells (Ht-pefc) Armentioning

confidence: 99%

Dynamic Operation of HT-PEFC: In-Operando Imaging of Phosphoric Acid Profiles and (Re)distribution

Eberhardt

Toulec

Marone

et al. 2015

J. Electrochem. Soc.

104

101

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Synchrotron based X-ray tomographic microscopy (XTM) is used for imaging and quantifying the redistribution of phosphoric acid (PA) in high temperature polymer electrolyte fuel cells (HT-PEFC) in-operando. The main focus of this work is the redistribution of phosphoric acid under dynamic load conditions. Therefore, two different load cycling protocols were applied and the transient redistribution within the fuel cell components was imaged. XTM, for the first time, revealed that the examined PBI based membrane system exhibits extensive electrolyte migration from cathode to anode under high current density operation. PA flooding of anode gas diffusion layer (GDL) and flow field channels occurred. Implications for technical applications and fuel cell degradation are discussed. Quantification of the migrated electrolyte is made by correlating in-operando grayscale values to ex-situ reference samples. High temperature polymer electrolyte fuel cells (HT-PEFC) are operating at temperatures up to 200• C using phosphoric acid (PA) doped polybenzimidazole (PBI) based membranes. This fuel cell technology has long been in the focus of research 1 due to advantages based on the higher operation temperature as compared to standard PEFCs, operating between 60-90• C. At the higher operating temperatures, the tolerance to fuel gas impurities increases significantly and operation with CO levels up to 3% and H 2 S up to 10 ppm can be achieved.2 This renders HT-PEFC especially suitable for stationary combined heat and power (CHP) applications, where a fuel processing unit can easily be thermally integrated and used for reforming hydrocarbon-based fuels without the need of additional gas clean-up. The advantageous characteristics of HT-PEFCs are also determined by the physico-chemical properties of the phosphoric acid electrolyte. First of all, PA has a low vapor pressure at these operating temperatures. This principally allows for long term operation without major electrolyte loss, an important aspect also specifically defined in the US Department of Energy's 2015 targets 3 (50'000 operating hours for stationary CHP systems). Phosphoric acid also exhibits excellent proton conductivity owing to a fast proton hopping mechanism. 4 Due to this inherent difference to PFSA-type membranes (water assisted shuttle mechanism), additional humidification is not necessary, which significantly reduces the complexity of HT-PEFC systems. However, only ca. 2 PA molecules per PBI repeating unit (PA/PBI) are directly interacting with the basic pyridinic nitrogen of PBI.5 However, PA doping levels are typically significantly higher, e.g., 5-10 for PA imbibed PBI films 6 and 20-40 for PBI membranes produced through the so-called poly-phosphoric acid (PPA) process.7 It can, therefore, be expected that the bulk of this phosphoric acid is more or less mobile within the molecular pores of the membrane. Hence, movement and redistribution of PA within the porous components (membrane, catalyst layer, micro-porous and gas diffusion layers) of the cell are expec...

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“…2) is most likely due to the ring breathing vibration of the benzene rings, as observed in Raman spectra of other polymers containing benzimidazole units. 33,38,39 Finally, the weak and broad peaks at lower wavenumbers, around 750 cm À1 , are due to C-H out-of-plane ring deformation 33,40 and are labeled with the letter Z in a dotted circle in Fig. 2a.…”

Section: Undoped Ab-pbimentioning

confidence: 99%

“…A similar signal at the same wavenumber but with a relatively higher amplitude was found in the Raman spectrum of concentrated phosphoric acid itself. 39 According to Li et al, the band is attributed to the presence of pure and free PA molecules. Thus, after a maximum degree of doping is reached, excess acid exists in the membranes.…”

Section: Phosphoric Acid Doped Ab-pbimentioning

confidence: 99%

Raman study of the polybenzimidazole–phosphoric acid interactions in membranes for fuel cells

Conti

Majerus

Noto

et al. 2012

Phys. Chem. Chem. Phys.

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Poly(2,5-benzimidazole) (AB-PBI) membranes are investigated by studying the FT-Raman signals due to the benzimidazole ring vibration together with the C-C and C-H out-of-and in-plane ring deformations. By immersion in aqueous ortho-phosphoric acid for different time periods, membranes with various doping degrees, i.e. different molar fractions of acid, are prepared. The chemical-physical interactions between polymer and acid are studied through band shifting and intensity change of diagnostic peaks in the 500-2000 cm À1 spectral range. The formation of hydrogen bonding networks surrounding the polymer seems to be the main reason for the observed interactions. Only if the AB-PBI polymer is highly doped, the Raman spectra show an additional signal, which can be attributed to the presence of free phosphoric acid molecules in the polymer network. For low and intermediate doping degrees no evidence for free phosphoric acid molecules can be seen in the spectra. The extent of the polymer-phosphoric acid interactions in the doped membrane material is reinvestigated after a period of one month and the stability discussed. Our results provide insight into the role of phosphoric acid as a medium in the conductivity mechanism in polybenzimidazole.

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Water uptake and acid doping of polybenzimidazoles as electrolyte membranes for fuel cells

Cited by 333 publications

References 32 publications

High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

Dynamic Operation of HT-PEFC: In-Operando Imaging of Phosphoric Acid Profiles and (Re)distribution

Raman study of the polybenzimidazole–phosphoric acid interactions in membranes for fuel cells

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