Disclosed herein are barium hafnate comprising proton-conducting electrolytes for use in solid oxide fuel cells. The disclosed electrolytes are also useful for electrolysis operations and for carbon dioxide tolerance.

Realized is an element having an electrolyte layer that is dense and has high gas barrier characteristics. A metal-supported electrochemical element includes at least a metal substrate as a support, an electrode layer formed on/over the metal substrate, a buffer layer formed on the electrode layer, and an electrolyte layer formed on the buffer layer. The electrode layer is porous and the electrolyte layer is dense. The buffer layer has density higher than density of the electrode layer and lower than density of the electrolyte layer.

Realized is an element having an electrolyte layer that is dense and has high gas barrier characteristics. A metal-supported electrochemical element includes at least a metal substrate as a support, an electrode layer formed on/over the metal substrate, a buffer layer formed on the electrode layer, and an electrolyte layer formed on the buffer layer. The electrode layer is porous and the electrolyte layer is dense. The buffer layer has density higher than density of the electrode layer and lower than density of the electrolyte layer.

A method of manufacturing a solid oxide fuel cell stack, including alternately disposing a plurality of single fuel cells, and a plurality of interconnectors disposed alternately and holding the alternately disposed plurality of single fuel cells and plurality of interconnectors between a pair of end members, forming a space between a first end member and a first interconnector, disposing a junction member composed of an elastic member and an electrically conductive member in the space, and urging a portion of an electrically conductive member and another portion of the electrically member against the first end member and the first interconnector so that a total thickness of the portion of the electrically conductive member, the another portion of the electrically conductive member, and the elastic member prior to being disposed in the space between the first end member and the first interconnector is greater than a height of the space.

A method of manufacturing a solid oxide fuel cell stack, including alternately disposing a plurality of single fuel cells, and a plurality of interconnectors disposed alternately and holding the alternately disposed plurality of single fuel cells and plurality of interconnectors between a pair of end members, forming a space between a first end member and a first interconnector, disposing a junction member composed of an elastic member and an electrically conductive member in the space, and urging a portion of an electrically conductive member and another portion of the electrically member against the first end member and the first interconnector so that a total thickness of the portion of the electrically conductive member, the another portion of the electrically conductive member, and the elastic member prior to being disposed in the space between the first end member and the first interconnector is greater than a height of the space.

A solid oxide electrolyzer electrolyte composition includes a scandia and ceria stabilized zirconia, containing 5 to 12 mol % scandia, 1 to 7 mol % ceria, and 80 to 94 mol % zirconia, or a yttria and ceria stabilized zirconia containing 3 to 10 mol % yttria, 1 to 6 mol % ceria, and 84 to 96 mol % zirconia.

A solid oxide electrolyzer electrolyte composition includes a scandia and ceria stabilized zirconia, containing 5 to 12 mol % scandia, 1 to 7 mol % ceria, and 80 to 94 mol % zirconia, or a yttria and ceria stabilized zirconia containing 3 to 10 mol % yttria, 1 to 6 mol % ceria, and 84 to 96 mol % zirconia.

A cell according to the present disclosure includes: a solid electrolyte layer including a first surface and a second surface opposite to the first surface; a fuel electrode on the first surface; an air electrode on the second surface; and a middle layer between the second surface and the air electrode. The middle layer=is a CeO.sub.2-type sintered body containing Si, the content of Si equivalent to or less than 150 ppm in terms of SiO.sub.2. A cell stack device includes a cell stack in which the plurality of cells is aligned. A module includes: a storage container; and the cell stack device that is housed in the storage container. A module housing device includes: an external case; the module and an auxiliary equipment that drives the module, which are housed in the external case.

A metal-supported electrolyzer includes an electrolysis cell that has, in stacked order, an electrode unit having a first solid oxide electrode layer, a solid oxide electrolyte layer that is proton-conductive in a temperature range of 650° C. or lower, and a second solid oxide electrode layer. A porous metal sheet in contact with the second solid oxide electrode layer supports the electrode unit, a metal separator sheet bonded to the porous metal sheet, and a metal interconnect backing the metal separator sheet.

In various embodiments, a solid oxide fuel cell is fabricated in part by disposing a functional layer between the cathode and the solid electrolyte.