The invention relates to a method for coating an organic or metal material by covalent grafting of at least one organic compound A having at least one aromatic group substituted with a diazonium function, on a surface of said material, characterized in that the material is porous or fibrillar having a geometric surface area of at least 10 cm2 of material, and in that said method includes a step of continuous imposition of a non-zero pulsed current in an intensiostatic mode on the surface of the material in order to electrochemically reduce the diazonium ion or ions. The invention further relates to the resulting composite materials and to the use of such materials for manufacturing electrodes.