Recent advances in direct alcohol PEMFCS

Abstract

Direct alcohol proton exchange membrane fuel cells (DAFCs) have been under active and extensive investigation worldwide due to the easy handle of the liquid fuels, which can be directly fed to the anode compartment and then oxidized here without any pre-reforming process, consequently making the system simple, light and compacted, moreover the higher mass power density of the alcohols. In the present work, the characteristics of the investigated alcohol fuels (methanol, ethanol, isopropanol) are described and compared from the requirements of the fuel in the long run. The main challenges for DAFC's development are the sluggish electrode reaction kinetics, especially for alcohol electrooxidation and fuel crossover from the anode to the cathode through the electrolyte membrane. PtRu and PtSn have been recognized to be the more active catalysts for methanol and ethanol electrooxidation respectively in PEMFCs. In the case of isopropanol, PtRu has always been adopted as the anode catalysts, but maybe it is not a desirable one. As far as fuel crossover phenomena are concerned, much effort has been devoted to modify the commonly used Nafion® electrolyte membrane or develop novel electrolyte to avoid or at least to decrease methanol crossover to some degree. However, methanol crossover is still one of the main obstacles for direct methanol fuel cell's commercialization. It was found that ethanol and isopropanol can also permeate through the electrolyte membrane although their crossover rates are much lower than that of methanol. Until now, there are no special measurements taken for preventing ethanol or isopropanol crossover. Membrane electrode assembly (MEA) is the heart of DAFCs. The progress in MEA's fabrication techniques and its effect on the cell performance have been summarized and evaluated. In order to overcome the challenges facing DAFC's development and accelerate its steps to commercialization, the development and breakthrough of the electrode the electrolyte material plays the key role.