High temperature proton exchange membranes based on polybenzimidazoles for fuel cells

Abstract

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.

High temperature (HT) polymer electrolyte membrane fuel cells (PEMFC) – A review

“…Conductivity for ABPBI has been reported as 0.08 S cm -1 at 140 o C with no hydration and 0.2 S cm -1 at 20%RH [57]. Extensive reviews of these materials have recently been published by Assensio et al [8] and Li et al [58]. Recently, Lin et al [59] [67].…”

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

“…The presence of free PA at a high doping level has been observed by several authors in phosphoric acid doped PBI membranes using various techniques. 7,9,44 The very low intensity of the signal shows that the large majority of PA molecules are interacting with the polymer chains, i.e. hydrogen bonds between the protonated imidazole rings in the polymer chain and the phosphoric acid molecules occur.…”

“…5 Acid-doped poly(2,2 0 -(m-phenylene)-5,5 0 -bibenzimidazole) (PBI) polymers have been studied as membranes for the use in High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs), since they can be used at temperatures as high as 200 1C without humidification. [6][7][8][9][10] PBI is a polymer containing a basic functionality that allows the uptake of acid, which is responsible, and required, for the proton conduction. PBI based acid-base membranes have been proposed by several groups using heteroand homogeneous synthesis.…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…This section is not meant as a complete review of electrolyte materials for HT-PEMFC. For a complete review, the reader is directed to several key reviews of polymer membranes for HT-PEMFC applications which have been written over the past 10 years, including Li [22], Bose [23], Asensio [24], and Herring [25] to name a few. As far as polymer electrolytes are concerned, currently Nafion TM is the baseline that is used as a reference material for PEM fuel cell performance.…”

“…While there are many candidate materials that are being evaluated as HT-PEM membranes, polybenzimidazole (PBI) is generally accepted as the "baseline" for both performance and durability for this new generation of PEM [22]. The conductivity of PBI membranes in the pure (unfilled) state is very low at about 10 −12 /cm [47,48].…”