A Reactive Fe-YSZ Coated Foam Device for Solar Two-Step Water Splitting

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 solar energy into clean hydrogen in sunbelt regions. An iron-containing yttrium-stabilized zirconia (YSZ) or Fe-YSZ is a promising working redox material for the two-step water-splitting cycle. $Fe2+$-YSZ is formed by a high-temperature reaction between YSZ and $Fe3O4$ supported on the YSZ at $1400°C$ in an inert atmosphere. $Fe2+$-YSZ reacts with steam and generates hydrogen at $1000–1100°C$ to form $Fe3+$-YSZ that is reactivated by thermal reduction in a separate step at temperatures above $1400°C$ under an inert atmosphere. In the present study, ceramic foam coated with Fe-YSZ particles is examined as the thermochemical water-splitting device to be used in a solar directly irradiated receiver/reactor system. The Fe-YSZ particles were coated on an Mg-partially stabilized zirconia foam disk, and the foam device was tested during the two-step water-splitting cycle; this was performed alternately at temperatures between $1100°C$ and $1400°C$⁠. The foam device was irradiated by concentrated visible light from a sun simulator at a peak flux density of $925kW/m2$ and an average flux density of $415kW/m2$ (total power input on the surface of the foam was 0.296 kW) in a $N2$ gas stream; subsequently, it was reacted with steam at $1100°C$ while heating by an infrared furnace. Hydrogen successfully continued to be produced in the repeated cycles.