A Two-Step Water Splitting With Ferrite Particles and Its New Reactor Concept Using an Internally Circulating Fludized-Bed

A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting and storing solar energy into a fuel in sunbelt regions. The ZrO₂-supported ferrite (or the ferrite/ZrO₂) powders exhibit superior performances on activity and repeatability of the cyclic reactions when compared to conventional unsupported ferrites. In the first step at 1400°C under an inert atmosphere, ferrite on ZrO₂ support is thermally decomposed to the reduced phase of wustite that is oxidized back to ferrite on ZrO₂ with steam in a separate second step at 1000°C. In this paper, a number of ZrO₂-supporetd ferrites, Mn-, Mg-, Co-, Ni- and Co-Mn-ferrites, are examined on activity. The NiFe₂O₄/ZrO₂ powder was found to have a greatest activity between them. This paper also describes a new concept of a windowed solar chemical reactor using an internally circulating fluidized bed of ferrite/ZrO₂ particles. In this concept, concentrated solar radiation passes downwards through the transparent window and directly heats the internally circulating fluidized bed. The exploratory experimental studies on this reactor concept are carried out in a laboratory scale for the thermal decomposition of NiFe₂O₄/ZrO₂ particle bed as part of two-step water splitting cycle.