NOVELTY - Catalyst comprises catalytic compounds comprising tetra-manganese-oxo clusters, and a conductive support substrate supporting catalytic compounds and capable of incorporating water molecules. At least some of the catalytic compounds supported by the support substrate are able to catalytically interact with water molecules incorporated into the support substrate.    USE - A catalyst for photo-anode for photo-electrochemical cell for water molecules photo-electrolysis for generating hydrogen and oxygen gases, or electricity (claimed).    ADVANTAGE - The catalyst is operable for over greater than or equal to 1000 (preferably greater than or equal to 100000) cycles.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a photo-anode for the electrolysis of water comprising an electrode substrate, and a catalyst;    (2) a photo-electrochemical cell for the electrolysis of water comprising a chamber capable of containing an aqueous electrolyte, a cathode in contact with the aqueous electrolyte when the chamber contains the aqueous electrolyte, and a photo-anode electrically connected to the anode in contact with the aqueous electrolyte when the chamber contains the aqueous electrolyte;    (3) a method of generating hydrogen and oxygen by photo-electrolyzing water comprising exposing photo-electrochemical cell to light radiation, applying an electric potential to the cell to produce hydrogen and oxygen gases and passing the hydrogen and oxygen gases produced from the cell to a fuel cell;    (4) a method of generating electricity comprising exposing photo-electrochemical cell to light radiation;    (5) a method for preparing a photo-electrochemical cell for use in photo-electrolysis of water comprising providing a conductive support substrate capable of incorporating water molecules, allowing catalytic compounds comprising tetra-manganese-oxo clusters to self-assemble on the support substrate so that at least some of the catalytic compounds are able to catalytically interact with the water molecules, coating the support substrate having the catalytic compounds assembled o an electrode substrate to provide a photo-anode, providing a cathode and forming an electrical connection between the photo-anode and the cathode, and providing an aqueous electrolyte between the photo-anode and the cathode to provide a photo-electrochemical cell; and    (6) a method for preparing a photo-electrochemical cell for the catalysis of water comprising providing a semiconductor layer, coating a layer comprising a photo-electrochemical relay system to the semiconductor layer, coating a layer of a conductive support substrate capable of incorporating water molecules to the semiconductor layer having the photo-electrochemical relay system, allowing catalytic compounds comprising tetra-manganese-oxo clusters to self-assemble on the support substrate so that at least some of the catalytic compounds are able to catalytically interact with the water molecules to form a photo-anode, providing an cathode and forming an electrical connection between the photo-anode and the cathode, and providing an aqueous electrolyte between the photo-anode and the cathode to provide a photo-electrochemical cell.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic proposal of mechanism of water oxidation by a tetra-manganese-oxo cubane catalytic compound.