NOVELTY - A seawater electrolysis separation/concentration device has a seawater reservoir moving below seawater after the reservoir removes particulate matter among the natural seawater. A separation seawater exhausting part ejects the separated seawater with total dissolved ingredient concentration lower than that of the natural seawater. A concentrated seawater exhausting part ejects the concentrated seawater with total dissolved ingredient concentration that is higher than that of the natural seawater. An ionic component is concentrated with the cell in the reservoir using a nanofiltration membrane.    USE - Seawater electrolysis separation/concentration device for use in a solar cell of a photoelectrochemistry device (claimed) to produce hydrogen.    ADVANTAGE - The method enables utilizing abundant seawater resources on earth, so that hydrogen manufacturing efficiency is maximized in an economic manner.    DETAILED DESCRIPTION - A seawater electrolysis separation/concentration device has a seawater reservoir moving below seawater after the seawater reservoir removes the particulate matter among the natural seawater. A nanofiltration membrane is equipped in a membrane cell, where the nanofiltration membrane concentrates an ionic component during separation of the seawater. A seawater feed port includes a seawater feeding line for supplying the seawater to the membrane cell from the seawater reservoir. A high pressure pump provides feed pressure, where the pump is installed in the line. A separation seawater exhausting part ejects the separation seawater with total dissolved ingredient concentration that is lower than that of the natural seawater. A concentrated seawater exhausting part ejects the concentrated seawater with total dissolved ingredient concentration that is higher than that of the natural seawater. The ionic component is concentrated with the membrane cell to the seawater reservoir. An INDEPENDENT CLAIM is also included for a photoelectrochemistry device comprising a solar cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a seawater electrolysis separation/concentration device.