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 BaZr_0.9Y_0.1O_3−x and CaZr_0.9In_0.1O_3−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 p_o2. 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 p_o2 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. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.