NOVELTY - A photoelectrochemical cell (19) has housing (1), separator (2) which divides space inside the housing into spaces (3) and (4), semiconductor photoelectrode (6) formed on conductive substrate (5), counter electrode (7), electrical connection portion (8), electrolyte solution (9) containing water, oxygen (or hydrogen) gas introduction pipe (10), oxygen (or hydrogen) gas discharge pipe (11) connected to upper portion of space (3), hydrogen (or oxygen) gas introduction pipe (12), and hydrogen (or oxygen) gas discharge pipe (13) connected to the upper portion of space (4).    USE - Photoelectrochemical cell is used for energy system (claimed) used as hydrogen supply source for fuel cell.    ADVANTAGE - The photoelectrochemical cell having improved hydrogen generation reaction efficiency can easily collect generated hydrogen. The photolysis efficiency of water is improved, when using the photoelectrochemical cell.    DETAILED DESCRIPTION - A photoelectrochemical cell has housing with translucent surface where light is irradiated, separator which divides space inside the housing into spaces (3) and (4), semiconductor photoelectrode arranged in the space (3) and formed on conductive substrate, counter electrode positioned in the space (4), electrical connection portion which connects the semiconductor photoelectrode and the counter electrode, electrolyte solution containing water in the spaces (3) and (4), oxygen (or hydrogen) gas introduction pipe whose one end is connected to lower portion of space (3), and other end is connected to oxygen (or hydrogen) gas supply section (15), oxygen (or hydrogen) gas discharge pipe connected to upper portion of space (3), hydrogen (or oxygen) gas introduction pipe whose one end is connected to lower portion of space (4), and other end is connected to hydrogen (or oxygen) gas supply section (16), and hydrogen (or oxygen) gas discharge pipe connected to the upper portion of space (4). An INDEPENDENT CLAIM is included for energy system.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the photoelectrochemical cell.    Housing (1)    Separator (2)    Spaces (3,4)    Conductive substrate (5)    Semiconductor photoelectrode (6)    Counter electrode (7)    Electrical connection portion (8)    Electrolyte solution (9)    Oxygen gas introduction pipe (10)    Oxygen gas discharge pipe (11)    Hydrogen gas introduction pipe (12)    Hydrogen gas discharge pipe (13)    Oxygen gas supply section (15)    Hydrogen gas supply section (16)    Photoelectrochemical cell (19)