Oxidative Degradation of Polybenzimidazole Membranes as Electrolytes for High Temperature Proton Exchange Membrane Fuel Cells

Abstract

Polybenzimidazole membranes imbibed with acid are emerging as a suitable electrolyte material for high‐temperature polymer electrolyte fuel cells. The oxidative stability of polybenzimidazole has been identified as an important issue for the long‐term durability of such cells. In this paper the oxidative degradation of the polymer membrane was studied under the Fenton test conditions by the weight loss, intrinsic viscosity, size exclusion chromatography, scanning electron microscopy and Fourier transform infrared spectroscopy. During the Fenton test, significant weight losses depending on the initial molecular weight of the polymer were observed. At the same time, viscosity and SEC measurements revealed a steady decrease in molecular weight. The degradation of acid doped PBI membranes under Fenton test conditions is proposed to start by the attack of hydroxyl radicals at the carbon atom linking imidazole ring and benzenoid ring, which may eventually lead to the imidazole ring opening and formation of small molecules and terminal groups for further oxidation by an endpoint oxidation.

Application of a Coated Film Catalyst Layer Model to a High Temperature Polymer Electrolyte Membrane Fuel Cell with Low Catalyst Loading Produced by Reactive Spray Deposition Technology

“…The use of phosphoric acid doped membranes to combat dehydration issues results in a highly acidic environment that can increase component degradation [2]. Several authors have noted a rapid degradation of cell performance for PBI-based HT-PEMFCs [21][22][23][24][25]. Two key processes related to this rapid degradation have been identified: catalyst agglomeration in the cathode due the presence of phosphoric acid and oxygen coupled with the high potential, and the direct degradation of the polymer.…”

Understanding ternary poly(potassium benzimidazolide)-based polymer electrolytes

“…During the last two decades this electrolyte system has been thoroughly characterized with respect to e.g. the chemistry of acid uptake and proton transport [8][9][10][11][12][13][14], thermal [15] and chemical stability [16,17], nanostructure [18] as well as gas permeability [19].…”

Fuel Cell Electrolytes of Polybenzimidazole Membranes Cross‐linked with Bis(chloromethyl) Arenes

“…As described by Liao et al. , the mass loss of PBI during the Fenton test is inversely proportional to the initial molecular weight over a test period of at least 280 h. It is also common that cross‐linked membranes show reduced rates of weight loss , , . This does not directly imply that cross‐linked membranes are inherently more oxidation resistant than their linear counterparts are, but rather indicates that soluble degradation products are formed at a lower rate.…”

“…The Fenton's test was carried out as described in literature , , . The samples (1 × 6 cm 2 ) were dried under vacuum at 110 °C for a minimum of 16 h to obtain the dry weight.…”