Novel two-step SnO2/SnO water-splitting cycle for solar thermochemical production of hydrogen

The production of hydrogen from a novel two-step thermochemical cycle based on SnO2/SnO redox reactions is presented. This process targets CO2-free hydrogen production by using renewable solar energy and water in a high-temperature water-splitting cycle. The cycle consists of a solar endothermic reduction of SnO2 into SnO(g) and O2 followed by a non-solar exothermic hydrolysis of SnO(s) to form H2 and SnO2(s). The objective of this study was to demonstrate this innovative concept for H2 production and to establish the potential of cycle implementation in an integrated solar chemical process. The reduction and hydrolysis reactions were experimentally tested in order to define optimal operating conditions, chemical conversion and hydrogen yield. The thermal reduction occurs under atmospheric pressure at about 1600 °C and over. The solar step encompasses the formation of SnO nanoparticles that can be hydrolysed efficiently in the temperature range 500–600 °C with a H2 yield over 90%. A preliminary process design is also proposed for cycle integration in solar chemical plants.