A novel process for hydrogen generation from water at high conversion is presented that is based on zinc hydrolysis as part of the two-step water-splitting thermochemical cycle of Zn/ZnO redox reactions. It encompasses formation of Zn nanoparticles by steam-quenching a Zn(g)flow followed by in situ hydrolysis. The process is experimentally demonstrated at the laboratory scale using a tubular aerosol flow reactor featuring a Zn-evaporation, a mixing and a reaction zone. In the reaction zone, operated at and just below the Zn(g) saturation temperature, Zn particles were formed and hydrolyzed with chemical conversion of up to 70%. The onset of H-2 formation is traced to ZnO formation by surface growth along the reactor axis using X-ray diffraction and microscopic analyses of Zn and ZnO particles collected on the reactor walls and effluents. (c) 2005 American Institute of Chemical Engineers.