Experimental study of SnO2/SnO/Sn thermochemical systems for solar production of hydrogen

A novel two-step thermochemical water-splitting cycle based on SnO2/SnO is proposed from the detailed study of the whole tin oxide systems involving three redox pairs. The thermal reduction of tin(IV) oxide occurs in the temperature range 1400-1600 degrees C following a zero order kinetic law of Arrhenius with an activation energy of 394.8 kJ mol(-1) and a pre-exponential factor of 8.32 X 10(8) g s(-1) at atmospheric pressure. The operating conditions that prevent gaseous stannous oxide (SnO) from recombining with O-2 are defined. The effect of a quenching device (water-cooled finger) is negligible whereas operation at low total pressure or low O-2 and SnO partial pressures leads to nearly pure SnO product. The comparison of SnO and metallic tin hydrolysis in a fixed bed reactor reveals a higher reaction rate in the case of SnO. Hydrolysis of these reduced compounds shows nearly complete conversion producing hydrogen by a solid/gas reaction proceeding at moderate temperature, thus easy to implement in a common reactor technology. (C) 2008 American Institute of Chemical Engineers.