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°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 × 108 g s−1 at atmospheric pressure. The operating conditions that prevent gaseous stannous oxide (SnO) from recombining with O2 are defined. The effect of a quenching device (water-cooled finger) is negligible whereas operation at low total pressure or low O2 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. © 2008 American Institute of Chemical Engineers AIChE J, 2008