Solid-state electrolyte sheet, solid oxide fuel cell, solid oxide electrolyzer cell, and methods of making the same

A solid-state electrolyte sheet comprising:

• stabilized zirconia grains comprising from about 3 mol % to about 12 mol % of a dopant selected from a group consisting of alumina, cerium oxide, gadolinium oxide, scandia, yttria, ytterbia, and combinations thereof;
• a thickness in a range from about 10 micrometers to about 300 micrometers;
• an ionic conductivity at 800° C. of 6.79 S/m or more;
• and
• an ionic conductivity at 835° C. of 8.8 S/m or more,
• wherein the stabilized zirconia grains exhibit a ratio of a cubic phase to a tetragonal phase (C/T ratio) from 0.15 to 0.50.

A method of making a solid-state electrolyte sheet comprising:

• casting a green tape comprising stabilized zirconia comprising from 3 mol % to 12 mol % of a dopant selected from a group consisting of alumina, cerium oxide, gadolinium oxide, scandia, yttria, ytterbia, and combinations thereof;
• firing the green tape to form the solid-state electrolyte sheet, wherein the firing comprises:
• heating the green tape at temperatures of 600° C. or more for 90 minutes or less with a maximum temperature of 1650° C. or less to form a sintered tape;
• and
• quenching the sintered tape from a temperature of from a starting temperature of 500° C. or more to final temperature of less than 100° C.