PROTON-EXCHANGE MEMBRANES BASED ON HETEROPOLY COMPOUNDS FOR LOW TEMPERATURE FUEL CELLS

Abstract

The review has analyzed the papers relative to heteropoly compounds, as solid proton conductors, for modification of polymer proton exchange membranes for their usage as low temperature fuel cells. The electrolyte functions and requirements, the structure and transport properties of perfluorinated proton exchange membranes which are the main candidates for practical applications are briefly considered. The main disadvantages of these membranes limiting their use are also highlighted. A special attention is given to the structure and properties of heteropoly compounds. The properties of heteropoly acids (phospho- and silicotungstic) containing anion with Keggin structure are discussed in details. In the main part of the review the methods of the preparation of the composite membranes based on perfluorinated and aromatic polymers and heteropoly compounds, the influence of the nature and content of the heteropoly compounds on their transport properties are analyzed. It is shown that the modification of polymer membranes by heteropoly compounds is one of the most promising methods to improve membranes performance. Due to its own high proton conductivity introduction of heteropoly compounds into polymer electrolytes in some cases can significantly improve proton conductivity, particularly at elevated temperatures, and reduce the methanol permeability. In the final part of the review the data on the use of composite polymer electrolytes with heteropoly compounds in the fuel cells and the influence of heteropoly compounds on the performance of the electrochemical devices are analyzed. It is shown that introduction of dopants inside of membrane can significantly increase both the operating temperature and performance of the fuel cell.