Synthesis of pyridinium-based ionic liquids for enhancement of oxygen reduction and methanol tolerance for Direct Methanol Fuel Cell

Abstract

This paper is about the synthesis and application of pyridinium-based ionic liquids for the enhancement of oxygen reduction and methanol tolerance on the Pt catalyst for DMFC. DMFC is a promising candidate for portable fuel cell because of the ease of transportation resulting from the liquid phase of methanol instead of gas phase. However, it has several unresolved problems that methanol crossover and the cost of Pt catalyst. To enhance the oxygen reduction reaction (ORR) activity and methanol tolerance of Pt catalyst, several ionic liquids were tested on the Pt surface. Herein, the monocyclic cation ionic liquids that are imidazolium, pyridinium, pyrrolidinium and piperidinium were synthesized. In addition, the multicyclic cation ionic liquids, such as isoquinolinium, phenanthrolinium and bipyridinium were also synthesized. The anion is fixed to bis(triflouoromethane)sulfonimide to analyze the effects resulted from cation structure such as saturation, aromaticity and protonation. The cation character was developed by alkylation with 1-boromobutane or by protonation with various acids. Alkylated and protonated cations were afforded in high yield over than 90%. And the yields of anion metathesis reaction were moderate to obtain the target ionic liquid. The ionic liquids were analyzed by proton, carbon and fluorine NMR followed by the measurement of melting point, viscosity, elemental analysis and single crystal XRD. The multicyclic ionic liquids can improve the ORR activity over three times. The multicyclic protonated ionic liquids also reduce the methanol oxidation current on the surface of the Pt catalyst.