Abstract
Modification of Nafion®-based samples with polyaniline (PANI) and positive charged ions could potentially allow achieving good proton conductivity at higher working temperatures what is observed in typical polymer electrolyte membrane fuel cells.In this work Nafion® polymer was modified with 1% polyaniline emeraldine salt and Li and Mg ions containing solutions. The influence of activation process and the type of ions on composites’ proton conductivity was investigated. To define the best composition the physiochemical properties of synthesized materials were determined by the means of thermogravimetric analysis, impedance spectroscopy, determination of water absorption and its kinetics, and FTIR. From the original samples the best results of σ=155 mS/cm were shown by Nafion®/PANI membrane what was modified by Li+ reduction solution. This membrane also had better thermal characteristic compared to other researched samples: membrane degradation starts on higher temperature interval.
Highlights
Nowadays commercially available for applications in fuel cells are perfluorinated polymers, such asNafion® made by DuPont Company
Permeability and ionic conductivity of the modified membranes were measured using electrochemical impedance spectroscopy; the thermal stability was determined by thermogravimetric analysis, and the presence of ions in polymer matrix was determined with FTIR spectroscopy
Membranes with more intensive 1508 cm-1 peak designate that composite polymer has more reduced fragments at 1643 and 3500 cm-1 proves the fact that polyaniline had changed its structure: these peaks are characteristic to pernigraniline form of PANI, so some of the fragments of emeraldine salt form have hanged to non-conductive fragments [5,7]
Summary
Nowadays commercially available for applications in fuel cells are perfluorinated polymers, such asNafion® made by DuPont Company. Membrane’s practical usage has been limited by Nafion® membrane’s disadvantages, e.g. low proton conductivity at low humidity, high fuel (hydrogen or methanol) cross-over and high price of Nafion® [1]. The ways to eliminate this disadvantage is to synthesize new materials or modify existing ones, both could be done with a set of methods and could bring desirable improvements of exploitation values. The focus of this paper is to synthesize and study the physical properties of Nafion®/PANI composite membranes, such as the water uptake, degradation and proton conductivity. Permeability and ionic conductivity of the modified membranes were measured using electrochemical impedance spectroscopy; the thermal stability was determined by thermogravimetric analysis, and the presence of ions in polymer matrix was determined with FTIR spectroscopy. The conductivity and thermal stability of all samples were compared with the unmodified Nafion® membrane as a reference
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