Carbon and fluorinated carbon materials are major constituents of phosphoric acid fuel cells and PEM fuel cells and the stability of these materials is critical for long life operation. Laboratory corrosion studies of separator plate materials were correlated with separator plate changes in commercial PAFC fuel cells. The addition of thin films of Teflon™ to the separator plates extends the life of the separator plates to 60,000+ hours through the formation of a temporary hydrophobic barrier. ESCA studies show the loss of hydrophobicity with time of PAFC electrodes to be a result of delamination of the Teflon from the carbon and not corrosion of the Teflon by phosphoric acid. The projected life of PAFC power plants has been confirmed by commercial operation of power plants for over 40,000 hours.