Comparison Studies of Reactivity on Nickel-Ferrite and Cerium-Oxide Redox Materials for Two-Step Thermochemical Water Splitting Below 1400°C

Abstract

A two-step thermochemical water splitting cycle using a redox system of non-volatile metal oxide is one of the promising processes for converting concentrated solar high-temperature heat into clean hydrogen in sun-belt regions. In the 1st step of the cycle or the thermal reduction step, metal oxide is thermally reduced to release oxygen molecules in an inert gas atmosphere at a higher temperature above 1400°C. In the second step or the water-decomposition step at a lower temperature, the thermally-reduced metal oxide reacts with steam to produce hydrogen. As the reactive redox metal oxide materials to be capable of working below 1400°C, nickel-doped iron oxides or Ni-ferrites supported on zirconia, and non-stoichiometric cerium oxides are the promising working materials. In the present work, a series of the nickel-ferrite redox materials of monoclinic-zirconia-supported, cubic-YSZ(yttrium-stabilized zirconia)-supported, and non-supported Ni-ferries and non-stoichiometric cerium oxide were compared on reactivity for two-step thermochemical water splitting cycle. The monoclinic-zirconia-supported Ni-ferrite produced the most quantity of hydrogen in the repeated cycles when the thermal reduction step was performed for 30 min at 1400°C and the water decomposition step for 60 min at 1000°C.

Review of Heat Transfer Research for Solar Thermochemical Applications

“…The peak hydrogen production rate from the MSPS is almost double that of the best rate yet reported in the literature and shown in Fig. 11 [28,76,[85][86][87]. The highly reactive MSPS is very suitable for solar thermochemical applications, and the model can provide an excellent tool for designing and controlling larger scale reactors.…”

“…Fig. 11 Comparison of peak hydrogen production rates for repeated redox cycles using different reactive materials [28,76,[85][86][87] medium becomes optically thinner as the particles shrink and this effect is more pronounced for smaller initial coal particles because these offer higher volume fractions to particle diameter ratios and, consequently, attain higher temperatures, reaction rates, and shrinking rates. A heat transfer numerical model was developed and experimentally validated for the steam-gasification of coal using a fluidized bed contained in a quartz tubular reactor that was directly exposed to concentrated thermal radiation [96].…”