Patent ID: 8894829

Claim:
A water electrolysis apparatus formed by stacking a plurality of unit cells, the unit cells each comprising: an electrolyte membrane; a pair of current collectors disposed respectively on opposite sides of the electrolyte membrane; a pair of separators stacked respectively on the current collectors; wherein a water flow field for supplying water is defined between one of the current collectors and one of the separators and a hydrogen flow field for producing hydrogen through electrolysis of the water is defined between the other current collector and the other separator; a water supply passage extending along a stacked direction in which the unit cells are stacked, for supplying the water to the water flow field; a discharge passage extending along the stacked direction, for discharging a remaining amount of the water from the water flow field; and a plurality of inlet joint channels interconnecting the water supply passage and the water flow field, wherein the inlet joint channels each have an opening of a circular cross-sectional shape and are arranged in parallel to each other, wherein the unit cells are stacked vertically, and water is supplied vertically upward through the water supply passage, wherein the number of the inlet joint channels of the unit cell that is positioned vertically higher in the apparatus is greater than the number of the inlet joint channels of the unit cell that is positioned vertically lower in the apparatus, and wherein the water supply passage has an inner wall surface at which the inlet joint channels are open, and an outer wall surface which faces the inner wall surface, the inner wall surface and the outer wall surface jointly forming an opening of an oblong cross-sectional shape.