NOVELTY - Water is contacted with nanoparticles of an inorganic photocatalyst compound (16) in a reaction zone (10) of a reaction chamber. Sunlight (2) is concentrated with an optical intensifier. The reaction zone is heated at one or more reaction temperatures of more than 140 degrees C using the concentrated sunlight. Water is exposed to the concentrated sunlight in the heated reaction zone in the presence of the inorganic photocatalyst compound at one or more reaction temperatures, such that reaction occurs and hydrogen molecules (18) are generated from water.    USE - Method for generating hydrogen molecules from water, used as fuel for fuel cell.    ADVANTAGE - Hydrogen molecules are economically and efficiently generated from water using photocatalyst having high durability.    DETAILED DESCRIPTION - Water is contacted with nanoparticles of an inorganic photocatalyst compound (16) in a reaction zone (10) of a reaction chamber. Sunlight (2) is concentrated with an optical intensifier such that intensity is increased by a factor of more than 2. The reaction zone is heated at one or more reaction temperatures of more than 140 degrees C using the concentrated sunlight. Water is exposed to the concentrated sunlight in the heated reaction zone in the presence of the inorganic photocatalyst compound at one or more reaction temperatures, such that reaction occurs and hydrogen molecules (18) are generated from water. The photocatalyst contains an element (E) chosen from copper, aluminum, titanium, gallium, cadmium, zinc, tungsten, iron, tin, silicon or their mixture. Water is in the form of water vapor. The sunlight is converted into thermal energy, and reaction zone is heated. The reaction zone is free of electrode for photoelectrochemical process. The nanoparticles are calcined nanoparticles containing an element (E). INDEPENDENT CLAIMS are included for the following:    (1) apparatus for photochemically generating hydrogen water, which has one or more reaction vessels (12) each reaction vessel having one or more channels for reacting water with sunlight in which each channel has an entrance end and an exit end for flowing water, in the form of liquid and/or gas through the channel, and photocatalyst attached to a surface located within an interior surface of the reaction vessel. The reaction vessel is formed of a material which is substantially transparent to visible and ultraviolet light. The reaction vessel is free of electrode for electrochemical reaction; and    (2) system for generating hydrogen molecules from sunlight and water, which has a reaction chamber having reaction zone, at least one optical intensifier which is in optical communication with the reaction zone and heats reaction zone at more than 140 degrees C, and nanoparticles of inorganic photocatalyst compound. The reaction chamber holds water and the nanoparticles, such that at least portion of the nanoparticles are contacted with water.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of hydrogen gas generation system.    Sunlight (2)    Optical intensification system (6)    Reaction zone (10)    Reaction vessel (12)    Water (14)    Photocatalyst compound (16)    Hydrogen molecules (18)