NOVELTY - Hetero-nanostructure (1115) comprises many connected and spaced-apart nano beams linked together at 90 degrees angle, where the nano beams including a conductive silicide core having an n-type photoactive hematite shell.    USE - The hetero-nanostructure is useful: as photoelectrochemical cell for producing hydrogen; as solar cell (claimed); as photocatalyst for pollutants treatment; as battery electrode; as anode material for lithium-ion battery; for high efficiency solar energy conversion; and for enhancing the efficiency of water splitting to generate hydrogen fuel.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a device (1100) for splitting water to generate hydrogen and oxygen comprising: a first compartment having a two-dimensional hetero-nanostructure, where the two-dimensional hetero-nanostructure has connected and spaced-apart nano beams, each nanobeam substantially perpendicular to another nanobeam, the nanobeams includes n-type photoactive hematite shell having a conductive core; and a second compartment having a p-type material, where the first compartment and the second compartment are separated by a semi-permeable membrane (1140); and    (2) fabricating a nanonet-based hematite hetero-nanostructure comprising: performing chemical vapor deposition to fabricate two-dimensional conductive silicide nanostructure, where at least one gas or liquid precursor materials carried by a first carrier gas stream react to form the nanostructure, and the nanostructure has a mesh-like appearance and includes connected and spaced-apart nano beams linked together at 90 degrees angle; annealing the nanostructure; and performing atomic layer deposition to deposit a conformal crystalline hematite around the nanostructure, where the film is present at 10-40 nm, and the gas or liquid precursor materials carried by second carrier gas stream react to form the hematite hetero-nanostructure.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of device for splitting water.    Device (1100)    Acidic compartment (1110)    Hetero-nanostructures (1115)    Basic compartment (1120)    Semipermeable membrane (1140)