The state-of-the-art of polymer electrolyte membrane fuel cell (PEMFC) technology is based on perfluorosulfonic acid (PFSA) polymer membranes operating at a typical temperature of 80 °C. Some of the key issues and shortcomings of the PFSA-based PEMFC technology are briefly discussed. These include water management, CO poisoning, hydrogen, reformate and methanol as fuels, cooling, and heat recovery. As a means to solve these shortcomings, high-temperature polymer electrolyte membranes for operation above 100 °C are under active development. This treatise is devoted to a review of the area encompassing modified PFSA membranes, alternative sulfonated polymer and their composite membranes, and acid−base complex membranes. PFSA membranes have been modified by swelling with nonvolatile solvents and preparing composites with hydrophilic oxides and solid proton conductors. DMFC and H₂/O₂(air) cells based on modified PFSA membranes have been successfully operated at temperatures up to 120 °C under ambient pressure and up to 150 °C under 3−5 atm. Alternative polymers are selected from silicon- and fluorine-containing inorganic polymers or aromatic hydrocarbon polymers and functionalized by sulfonation. The sulfonated hydrocarbons and their inorganic composites are potentially promising for high-temperature operation. High conductivities have been obtained at temperatures up to 180 °C. Acid−base complex membranes constitute another class of electrolyte membranes. A high-temperature PEMFC based on H₃PO₄-doped PBI has been demonstrated for operation at temperatures up to 200 °C under ambient pressure. The advanced features include high CO tolerance, simple thermal and water management, and possible integration with the fuel processing unit.

The CO poisoning effect on carbon-supported platinum catalysts (at a loading of 0.5 mg <mml:math display="inline"><mml:mi mathvariant="normal">Pt</mml:mi><mml:mo>/</mml:mo><mml:msup><mml:mi mathvariant="normal">cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:math>Pt/cm2 per electrode) in polymer electrolyte membrane fuel cells (PEMFCs) has been investigated in a temperature range from 125 to 200°C with the phosphoric acid-doped polybenzimidazole membranes as electrolyte. The effect is very temperature-dependent and can be sufficiently suppressed at elevated temperature. By defining the CO tolerance as a voltage loss less than 10 mV, it is evaluated that 3% CO in hydrogen can be tolerated at current densities up to <mml:math display="inline"><mml:mn>0.8</mml:mn><mml:mo>A</mml:mo><mml:mo>/</mml:mo><mml:msup><mml:mi mathvariant="normal">cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:math>0.8A/cm2 at 200°C, while at 125°C 0.1% CO in hydrogen can be tolerated at current densities lower than <mml:math display="inline"><mml:mn>0.3</mml:mn><mml:mo>A</mml:mo><mml:mo>/</mml:mo><mml:msup><mml:mi mathvariant="normal">cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup><mml:mo>.</mml:mo></mml:math>0.3A/cm2. For comparison, the tolerance is only 0.0025% CO (25 ppm) at 80°C at current densities up to <mml:math display="inline"><mml:mn>0.2</mml:mn><mml:mo>A</mml:mo><mml:mo>/</mml:mo><mml:msup><mml:mi mathvariant="normal">cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup><mml:mo>.</mml:mo></mml:math>0.2A/cm2. The relative anode activity for hydrogen oxidation was calculated as a function of the CO concentration and temperature. The effect of <mml:math display="inline"><mml:msub><mml:mo>CO</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>CO2 in hydrogen was also studied. At 175°C, 25% <mml:math display="inline"><mml:msub><mml:mo>CO</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>CO2 in the fuel stream showed only the dilution effect. © 2003 The Electrochemical Society. All rights reserved.