Hydrogen generation from water using Si nanopowder fabricated from swarf

Si nanopowder is fabricated from Si swarf by the simple beads milling method. Si nanopowder possesses the maximum crystallite size distribution at 7 nm and the average diameter of 12 nm. Fabricated Si nanopowder easily reacts with water, resulting in generation of hydrogen. The hydrogen generation rate strongly depends on pH value of the solutions and the temperature. When the pH value and the reaction temperature are set at 13.0 and 50 °C, respectively, the hydrogen evolution rate in the initial 1 min reaches to ∼580 mL/min g, i.e., more than 1000 mL hydrogen is generated from 1 g Si nanopowder in 2 min. Hydrogen generation stops when a thick SiO2 layer is formed on the surface of Si nanopowder. Analysis of evolved hydrogen volume versus the reaction time shows that in the initial reaction period, dissolution of Si by OH− ions to form soluble H2SiO4 2− ions and hydrogen molecules is the dominant reaction, while in the subsequent period, the reaction of Si nanopowder with OH− ions forms SiO2, leading to generation of hydrogen molecules and electrons in the SiO2 conduction band. Generated electrons are accepted by water molecules, resulting in formation of hydrogen and OH− ions.