Direct methanol fuel cell (DMFC) is being widely investigated and considered as a prospective and potential power source for the application in traortation, portable electronics, residential power sources. However, DMFC still has some problems that need to be solved. At the present time, the most important disadvantages for DMFC are the reduce kinetics at the electrodes mainly at the oxygen electrode, the sensitivity of the electrodes to carbon monoxide poising and low operating temperature, that lead to need high Pt catalyst and high cost. Thus, studying on the disadvantages removal of DMFC is an important subject. One method for enhancing the performance of liquid-type fuel cell is the adding of additives. In recent years, utilization of ionic liquids (ILs) as electrolyte additives and membrane modifies is considered as a new topic in studies of batteries and fuel cells. ILs are molten salts resulting from the combination of organic cations and various anions. They are non-volatile and non-flammable, have high thermal stability. Considering their electrochemical properties, ILs have electrochemical windows that are much greater than those for aqueous electrolytes. Resently many researches have concentrated for using of ILs in PEMFC composite membrane. This sterategy, operating temperature of PEMFC raise to over 100 o C without humidification. Due to interaction between electrodes and membranes at membrane electrode assembly, catalysts are affected by the presence of ILs in the composite membranes. In the present work, for the first time, the effects of four ILs as a fuel additive were studied in DMFC. A family of alkylammonium hydrogen sulfate ILs, which are different in the number of alkyl chain, is investigated with the aim to compare effects of their structure on the electrochemical behavior of methanol electrooxidaton. Effect of ILs structure on the performance of DMFCs anode has been studied by different electrochemical methods such as cyclic voltammetry (CV), Chronoamperometric (CA), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS). The results show that with increasing of alkyl chain of ILs cation, the electroactivity of catalyst decrease in methanol oxidation reaction related to beetle active sites of catalyst by cation of ILs. A possible explanation is that with increasing the number of alkyl chain, bulk resistance increased and proton transfer to the catalyst surface decreases as well. Finally by analyzing test results it could be concluded, Although ILs successfully employed in composite membrane at PEMFC, but they have negative effect on intrinsic activity of DMFC and PEMFC anode catalyst.
