(Invited) Applications of Solid Electrolyte Membranes in Heterogeneous Catalysis. Electrochemical Reaction and Separation
The production of hydrogen with simultaneous conversion of methane to C2 hydrocarbons was studied in a solid state oxygen ion (O2-) conducting cell at temperatures between 700 oC and 850 oC. Methane, diluted in nitrogen was introduced over the anode (Ag) and steam, also diluted in nitrogen, was introduced over the cathode (Pt). When oxygen was electrochemically “pumped” from the cathode to the anode, steam was electrolyzed to produce gaseous H2 while CH4 was converted to C2H6, C2H4 and CO2. At the anode, C2yields exceeding 8% were obtained while an up to 65% conversion of steam was achieved at the cathode.
The electrochemical synthesis of ammonia was studied in a proton conducting solid electrolyte cell. The BaZr0.7Ce0.2Y0.1O2.9 (BZCY72) proton conducting ceramic was used as the electrolyte with a Ni-BZCY72 cermet and a Pt film serving as cathodic and anodic electrodes, respectively. The reaction was studied at atmospheric pressure and at temperatures between 450 oC and 700 oC, under both, open- and closed-circuit conditions. A peculiar reaction rate enhancement was observed when the cell returned to open-circuit after operating under closed-circuit for a certain time. A possible explanation of this new phenomenon is that a fraction of protons electrochemically transported to the cathode, is "stored" in the Ni-BZCY72 electrode in the form of a highly reactive hydride which, upon current interruption, reacts with adsorbed N species to produce ammonia.