Electrochemical reforming of CH4–CO2 mixed gas using porous yttria-stabilized zirconia cell

概要

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Flow rate and compositions of outlet gas and carbon deposition in the cell were studied upon the electrochemical reforming of 50% CH4–50% CO2 mixed gas using a cell of Ru–yttria-stabilized zirconia (YSZ) anode/porous 8 mol %-YSZ electrolyte/Ni–YSZ cathode system at 400–800°C under 1.0 V/cm of electric field strength. The supplied mixed gas of 95–97% changed to H2 and CO fuels at 800°C (CH4 + CO2 → 2H2 + 2CO). As a parallel reaction, pyrolysis of CH4 occurred over a Ni cathode to produce carbon powder in the cell (CH4 → C + 2H2), which decreased the flow rate of outlet gas at a high temperature. The above results were compared with the previously measured results with a porous Gd-doped ceria cell (mixed conductor of O2− ions and electrons). In the GDC cell, a part of deposited carbon was removed as CO gas by the reaction with O2− ions formed from CO2 gas in the cathode (CO2 + 2e− → CO + O2−, C + O2− → CO + 2e−) and the electrons produced were transported to the anode through the mixed conductor electrolyte film.