NOVELTY - A porous film material comprises substrate coated with lanthanum molybdate base. The porous polycrystalline film has thickness of 10 mu m to 50 nm. The lanthanum molybdate base comprises grains of diameter 10-90 nm. The pores in the film material has pore diameter of 1 mu m to 20 nm.    USE - A porous film material for medium temperature fuel cells, oxygen sensors and catalyst or oxidant.    DETAILED DESCRIPTION - A porous film material comprises substrate coated with lanthanum molybdate base of formula (La2-xAx) (Mo2-yDy)O9-delta. The porous polycrystalline film has thickness of 10 mu m to 50 nm. The lanthanum molybdate base comprises grains of diameter 10-90 nm. The pores in the film material has pore diameter of 1 mu m to 20 nm.    A=lanthanum-site dopant, preferably K, Ba, Gd, Nd, Bi, or Ca;    D=molybdenum-site dopant, preferably Fe, Mn, W, Re, Cr, or V; and    x, y=0-2.    An INDEPENDENT CLAIM is included for a method for preparing the porous film material comprising:    (A) mixing lanthanum, oxides or nitrate or acetate of lanthanum-site dopant, ammonium molybdate and oxides or nitrate or acetate of molybdenum-site dopant, adding mixture to organic solvent to prepare an organic solution, adding nitric acid to the solution to dissolve the lanthanum, dripping lanthanum nitrate solution to organic solution of ammonium molybdate while stirring, and dripping organic solution of lanthanum-site dopant and organic solution of molybdenum-site dopant to obtain solution of organic system;    (B) adding complexing agent into solution of organic system, stirring to obtain colloidal sols, where the complexing agent and total metallic ions in the solution of organic system are at mole ratio of 1:0.5-2, adjusting pH to 4-7 and stirring at 80-130 degrees C for greater than or equal to 2 hours to obtain film coating colloid whose concentration is 0.1-0.5 M; and    (C) coating a substrate with film coating colloid, placing the coated substrate at 300-450 degrees C for 3 minutes to 2 hours, repeating the process at least once, heating to 600 degrees C, sintering at 500-750 degrees C for 3-25 hours.