Abstract: A planar solid electrolyte oxygen separator includes a first end plate formed with an oxygen outlet, a second end plate, two solid electrolyte cells disposed between the first and second end plates, and a planar interconnector disposed between the solid electrolyte cells. Each of the solid electrolyte cells includes two electrode layers, a metal-oxide-based electrolyte layer, and a through hole that is aligned with the oxygen outlet. The planar interconnector includes an upper portion having upper main channels and an upper passage, a lower portion having lower channels, and a connecting passage fluidly connected to the upper passage and the lower channels.