NOVELTY - Organic solutions comprise metal (IV) salts and oxo acids of phosphorus from which, after evaporation of the solvent, insoluble compounds of can be obtained.    USE - Useful for the insertion of nano-particles, preferably a large variety of lamellar nano-particles of tetravalent metal salts, preferably phosphate-phosphonates, within the pores of polymeric or inorganic porous membranes, or in the membrane/electrode interfaces useful for electrical vehicles and/or for portable electrical devices (claimed).    ADVANTAGE - The inventive organic solutions produce composite membranes with improved global performance of ionomeric membranes of the state of the art in hydrogen, indirect methanol and direct methanol fuel cells.    DETAILED DESCRIPTION - Organic solutions comprise metal (IV) salts and oxo acids of phosphorus from which, after evaporation of the solvent, insoluble compounds of general composition M(IV)(O3P-G)2-n(O3P-R1-X)n can be obtained.    M(IV) = tetravalent metal;    -G = generic inorganic or organic group;    -R1- = organic group;    -X = acid group;    n = 0-1.5.    INDEPENDENT CLAIMS are also included for:    (a) a method for the filling of porous membranes with tetravalent metal salts, especially phosphate-phosphonates, comprising preparing the organic solution that may contain a polymer and/or an ionomer of the state of the art; impregnating the porous membrane with the solution; eliminating the solvent; and repeating the impregnation and the elimination until the desired percentage of pore filling is obtained;    (b) proton conducting composite membranes made of polymeric or inorganic porous membranes with pores filled with tetravalent metal salts, especially phosphate-phosphonates, or mixtures of the compounds with a proton conducting ionomer and specially prepared using the solutions as above;    (c) composite membranes comprising a porous ceramic membrane partially filled with a tetravalent metal salt, preferably phosphate-phosphonate as above, exhibiting catalytic activity;    (d) a method for the preparation of nano-polymers and nano-ionomers comprising preparing an organic solution having one of the compositions reported above and at the same time containing a polymer and/or ionomer of the state of the art; and eliminating the solvent by evaporation or with a non-solvent of the polymer or ionomer;    (e) use of proton conducting membranes constituted by inorganic or polymeric porous membranes with pores filled with tetravalent metal salts, preferably phosphate-phosphonates and of membranes constituted by nano-polymers in electrochemical devices specifically planned for generating electrical energy from the oxidation of a fuel; and    (f) use of proton conducting composite membranes and composite membranes in catalytic membrane reactors.