NOVELTY - Cerium-containing nano-coating composition (I) comprises: an amorphous matrix including one or more of cerium oxide, cerium hydroxide, and cerium phosphate; and crystalline regions including one or more of crystalline cerium oxide, crystalline cerium hydroxide, and crystalline cerium phosphate. The diameter of each crystalline region is less than 50 nm.    USE - (I) is useful in photocatalysis, corrosion resistant coatings, chemical degradation, UV protective coatings or sunscreens, solid oxide fuel cells, sensors, and other solid state electrochemical devices, and as photocatalysts for toluene oxidation, azo dye degradation, and water decomposition or splitting.    ADVANTAGE - (I) is capable of self-healing surface cracks, has an achievable band gap differential of 2-4 eV, and is capable of absorbing light having a range of threshold absorption wavelengths up to 590 nm and photocatalytically splitting water at ambient temperatures and pressures. The band gap is increasable by exposing the composition to sunlight at ambient temperatures and pressures. (I) has improved characteristics including increased electric conductivity or corrosion resistance.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for producing (I), comprising immersing a metal substrate (111) in a cerium-containing aqueous bath having depositing a cerium-containing conversion coating on the substrate, spontaneously depositing the nano-coating on the substrate, where the nano-coating includes the amorphous matrix and the crystalline regions excluding crystalline cerium phosphate, and immersing the nano-coated substrate in a phosphate-containing solution sufficient to convert the deposited nano-coating to a phosphated nano-coating including the amorphous matrix and the crystalline regions.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of a method for preparing a nano-structured composition.    Metal substrate (111)    Surface (112)    Grinding the substrate (120)    Acid treating the substrate (130)    Alkaline treatment of the substrate. (140)