Fuel Cell-Related Membrane Problems

Yet Nafion-type membranes do exhibit certain defects. The chief defect responsible for lack of a really broad commercialization of fuel cells containing such membranes is their high cost (about 700/m ). This figure is unlikely to come down soon, since it is founded in a highly complex manufacturing technology. 

Important further shortcomings of Nafion-type membranes are the following  

The protonic conductivity and mechanical properties are highly sensitive to the membrane s moisture content, which in turn is related to that of the ambient atmosphere, which implies that complex systems must be used to maintain the proper water balance in a membrane-type fuel ceU. 

In view of point (1), these membranes cannot be used at temperatures above 130 to 150°C. 

These membranes are highly permeable to methanol and certain other substances likely to be used in fuel cells. 

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This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

Professor S. Srinivasan and his team have studied the effect of pressure and characteristics of the current-potential relations in a hydrogen-oxygen fuel cell with a proton exchange membrane (Y. W. Rho, O. A. Velev, S. Srinivasan, and Y. T. Kho,./. Electrochem. Soc. 141 2084, 2089, 1994). In this problem, it is proposed to study the applicability of the theoretical dependence of the cell potential as a function of pressure. The temperature is 25 °C and it may be assumed that the pressure of the gas in each of the compartments, i.e., the anodic compartment (hydrogen) and the cathodic compartment (oxygen), are the same, Pn =Po P- For the formation of water in its standard state, the relevant thermodynamic quantities are ... 

The main problems regarding the replacement of batteries by direct alcohol fuel cells are related to the largest volume required by the fuel cells, as compared to the batteries which have become highly compact (because DAFCs have not reached yet high efficiencies), elimination of residues of the methanol partial oxidation (generally mixtures of water with formic acid, methyl formate, and formaldehyde), and the high temperature which can reach the DAFC (up to around 85 °C for cells using Nafion membranes) [11, 12]. 

Membrane. Perfluorosulfonic acid (PFSA) is the most commonly used membrane material [4], PFSA membranes are relatively strong and stable in both oxidative and reductive environments, since the structure of PFSA is based on a PTFE backbone. The conductivity of a well-humidified PFSA membrane can be as high as 0.2s cm. As is well known, fuel cell operation at elevated temperatures can increase the rates of reaction, reduce problems related to catalyst poisoning, reduce the use of expensive catalysts, and minimize problems due to electrode flooding. Unfortunately, a PFSA membrane must be kept hydrated to retain its proton conductivity. Moreover, a PFSA membrane is alcohol permeable if it is used in DAFCs. Because of the disadvantages of PFSA membranes, many alternatives have been proposed [106]. Five categories of membranes are classified (1) perfluorinated, (2) partially fluorinated, (3) non-fluorinated, (4) non-fluorinated composite, and (5) others. 

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