Alpha-Pbo2-Type Niobate As Efficient Cathode Materials For Steam And Co2 Electrolysis

alpha-PbO2-type Mn0.5Ti0.5NbO4-based oxides are studied as cathode materials in solid oxide electrolysis cell (SOEC) for the direct electrolysis of steam or CO 2 at 800 degrees C. Comparison between Mn0.5Ti0.5NbO4 and the Fe-doped ones, Fe0.3Mn0.35Ti0.35NbO4 and Fe0.6Mn0.2Ti0.2NbO4, indicates that the Fe3+ doping increases the electric conductivity in air but decreases the stability of the alpha-PbO2 structure in reducing atmosphere as in Fe0.6Mn0.2Ti0.2NbO4. The electric conductivity in reducing atmosphere is found to be ascribed to Ti4+-O-Ti3+ and Fe3+-O-Fe2+ in Mn0.5Ti0.5NbO4 and Fe doped ones, respectively. The steam or CO2 electrolsysis indicates that 30% Fe3+ substitution for Mn/Ti decreases the polarization resistance at low bias, but 60% Fe doping increases the polarization resistance dramatically than Mn0.5Ti0.5NbO4. The excessive Fe3+ doping is found to induce the phase transformation and delamination on the cathode/electrolyte interface under a cathodic current. The electrolyser with Fe0.3Mn0.35Ti0.35NbO4 cathode on zirconia-based electrolyte imparts a stable current density of 2.32 Acm(-2) at -1.6 V if Ar-88% H2O is used as feeding gas. Analysis of the gas product indicates that H-2 is produced and the Faradaic efficiency at -1.4 V and -1.6 V is found to be 100% and 93%, respectively.