Advanced Corrosion Resistant Materials for Electrochemical Applications

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Deposition of thin diamond films by plasma assisted chemical vapor deposition (PACVD) is a rapidly emerging area of technology being pursued in The United States, Japan and the Soviet Union. Diamond films have unique chemical and physical properties such as oxidation resistance and hardness. Boron-doped diamond films grown by PACVD can have electrical resistivities approaching 1 ohm-cm. Pore-free, adherent films of less than 1-micron thickness have already been deposited on tungsten substrates. The goal of this study is to evaluate these films as an electrically conductive, corrosion-resistant coating for bipolar separator plates (carbon-carbon composites) in phosphoric acid fuel cells (PAFC). Present plate designs fail because of corrosion of the carbon filler and acid absorption by the plate which leads to eventual shoring of the cell. Thin diamond films deposited on the bipolar plates, in addition to being corrosion resistant, can also act as a barrier layer, thus preventing acid absorption.