NOVELTY - The photo-electrode (100) has a photo catalyst layer (13) which is formed on electro-conductor layer (12). The energy difference between vacuum level and Fermi level of electro-conductor layer is smaller than energy difference between vacuum level and Fermi level of photo catalyst layer, when photo-catalyst layer consists of n-type semiconductors. The energy difference between vacuum level and Fermi level of electro-conductor layer is larger than energy difference between vacuum level and Fermi level of photo catalyst layer, when photo-catalyst layer consists of p-type semiconductors.    USE - Photo-electrode for photo-electrochemical cell of energy system (all claimed).    ADVANTAGE - The catalyst activity and crystallinity of the photo-electrode can be improved effectively. The light utilization efficiency of the photo-electrode can be improved effectively. The charge separation efficiency of the photo-electrochemical cell can be improved. The crystallinity of the electro conductor layer is increased, in order to reduce resistance value of the photo-electrode. The quantum efficiency of hydrogen generation reaction can be improved by irradiation of light. The generation of current leakage in the photo-electrochemical cell can be suppressed.    DETAILED DESCRIPTION - The photo-catalytic layer is provided with nitride semiconductor containing a tantalum element and oxy-nitride semiconductor. The oxy-nitride semiconductor is chosen from group consists of the oxy-nitride containing tantalum element, oxy-nitride containing niobium element, and oxy-nitride containing a titanium element. INDEPENDENT CLAIMS are included for the following:    (1) photo-electrochemical cell which has a counter electrode that electrically connected with conductor layer contained in photo-electrode. A container accommodates photo-electrode and counter electrode;    (2) energy system which has a hydrogen reservoir that is connected with photo-electrochemical cell by piping, in order to store hydrogen generated within photo-electrochemical cell. The fuel battery is connected with hydrogen reservoir, in order to convert hydrogen into electric power;    (3) method for manufacturing photo-electrode; and    (4) hydrogen generation method.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the photo-electrode.    Substrate (11)    Electro-conductor layer (12)    Photo catalyst layer (13)    Photo-electrode (100)