High-temperature proton conductors: hydrogen injection and pumping

The electrochemical injection of hydrogen into inert gases was demonstrated using tubes of the high-temperature proton conductors BaZr0.9Y0.1O3−x and CaZr0.9In0.1O3−x. By applying a voltage with the right polarity protons can be driven to the inner electrodes. Recombination of the protons at the cathode leads to high-purity hydrogen which is injected into the gas stream. Since most inert gas streams contain a small amount of oxygen, hydrogen evolving at the cathode can react with that O2 effectively lowering the po2. Thus, by increasing the proton current gas titration curves are obtained in analogy to strong acid — strong base titrations. Modelling of such curves is presented. This method of reducing the effective po2 by adding hydrogen in a controlled manner is discussed and compared with the classic technique of pumping oxygen electrochemically out of a gas stream using Y-stabilized zirconia tubes. Steam electrolysis was also demonstrated as well as the proton pick-up of the tubes by exposure of one side of the tubes to ethanol or acetone vapors.