Zirconia-bismuth oxide graded electrolyte

A solid state fuel cell/electrolyzer comprising:

• a composite sintered electrolyte having a first outer layer consisting essentially of ZrO.sub.2 and Y.sub.2 O.sub.3 or CeO.sub.2 with a second outer layer consisting essentially of Bi.sub.2 O.sub.3 and a suitable metal oxide dopant and with one or more inner layers having compositions intermediate said outer layers;
• a first porous electrode adherent to said first outer layer, said electrode being suitable for contact with a gaseous fuel containing hydrogen;
• a second electrode which is porous or pervious to oxygen molecules, said second electrode adherent to said second outer layer;
• means to heat said electrolyte to a temperature of about 700.degree.-800.degree. C.;
• conductor means to conduct current to or from said electrodes;
• containment means for containing the respective gases in contact with their respective electrodes and insulated from one another;
• gaseous fuel introduction means for introducing fuel to said first electrode;
• and
• oxygen introduction means for introducing oxygen to said second electrode.

A sintered ceramic article of a graded composition comprising:

• a first outer layer consisting essentially of about 95% zirconia and about 5% of an oxide mixture of Bi.sub.2 O.sub.3, and Y.sub.2 O.sub.3 wherein the molar ratio of Bi.sub.2 O.sub.3 to Y.sub.2 O.sub.3 is from about 3:1 to about 3:2 and wherein said zirconia is substantially present as cubic zirconia;
• a second outer layer consisting essentially of an oxide mixture of Bi.sub.2 O.sub.3 and Y.sub.2 O.sub.3 wherein the molar ratio of Bi.sub.2 O.sub.3 to Y.sub.2 O.sub.3 is from about 3:1 to about 3:2;
• and
• at least two intermediate layers wherein a first intermediate layer adjacent said first outer layer consists essentially of about 65-80% ZrO.sub.2 and about 20-35% of an oxide mixture of Bi.sub.2 O.sub.3 and Y.sub.2 O.sub.3 wherein the molar ratio of Bi.sub.2 O.sub.3 to Y.sub.2 O.sub.3 is from about 3:1 to about 3:2 and a second intermediate layer adjacent said second outer layer and in contact with said first intermediate layer, said second intermediate layer consisting essentially of about 15-25% ZrO.sub.2 and about 75-85% of an oxide mixture of Bi.sub.2 O.sub.3 and Y.sub.2 O.sub.3 wherein the molar ratio is from about 3:1 to about 3:2, said layers forming an integral unit.

A process for forming a sintered ceramic article of a graded composition comprising:

• forming a first outer layer consisting essentially of about 95% zirconia powders and about 5% of a powder mixture of Y.sub.2 O.sub.3 and a sufficient amount of a bismuth compound which converts upon sintering to Bi.sub.2 O.sub.3 to be present in a ratio of Bi.sub.2 O.sub.3 to Y.sub.2 O.sub.3 of from about 3:1 to 3:2;
• forming a first intermediate layer in intimate contact with said first outer layer;
• said first intermediate layer consisting essentially of about 75-95% of ZrO.sub.2 powders and about 5-25% of a powder mixture of Y.sub.2 O.sub.3 and a sufficient amount of a bismuth compound which converts upon sintering to Bi.sub.2 O.sub.3 to be present in a ration of Bi.sub.2 O.sub.3 to Y.sub.2 O.sub.3 of about 3:1 to 3:2;
• forming a second intermediate layer in intimate contact with said first intermediate layer consisting essentially of about 35-45% ZrO.sub.2 and about 55-65% of a powder mixture of Y.sub.2 O.sub.3 and a sufficient amount of bismuth compound which converts upon sintering to Bi.sub.2 O.sub.3 to be present in a ratio of Bi.sub.2 O.sub.3 to Y.sub.2 O.sub.3 of about 3:1 to 3:2;
• forming a second outer layer in intimate contact with said second intermediate layer consisting essentially of a powder mixture of Bi.sub.2 O.sub.3 and Y.sub.2 O.sub.3 wherein the molar ratio of Bi.sub.2 O.sub.3 and Y.sub.2 O.sub.3 is about 3:1 to 3:2 upon sintering of the ceramic article;
• pressing said layers together to form a green ceramic article;
• and
• hot pressing said green ceramic article at a sufficient temperature and at a sufficient pressure to form a sintered article.