Process for preparing proton-conducting clay particles and composite material comprising such particles

Process for preparing proton-conducting clay particles, successively comprising the following steps:

• a) providing clay particles in the form of a powder;
• b) activating the clay particles, by subjecting said particles to a gas plasma, said particles thus constituting activated particles;
• and
• c) contacting said activated particles with a solution comprising at least one compound comprising at least one group chosen from —PO3H2, —CO2H and —SO3H and salts thereof and comprising at least one group capable of grafting onto a surface of said activated particles,
• whereby proton-conducting clay particles in the form of a powder are obtained having on their surfaces at least one compound comprising at least one group chosen from —PO3H2, —CO2H and —SO3H and salts thereof, and wherein the at least one compound is grafted to the clay particles through covalent chemical bonds.