(171c) Metal Oxide Based Solar Driven Thermochemical Water Splitting Cycle: Solar Reactor Efficiency Analysis

The conversion of solar energy into chemical energy in the form of alternative fuel such as H2 provides a promising option for sustainable future energy pathways. Hydrogen can be produced with solar thermal energy via water splitting reactions. Hydrogen used in this manner is an energy carrier. Its advantages include a high energy density (on a mass basis) and non-polluting nature. The metal oxide (MO) based two-step solar thermochemical cycle is a potentially advantageous way to produce hydrogen via water splitting. In the past, several MO-based redox systems were theoretically and experimentally studied as potential thermochemical water splitting reactions. These include zinc oxide cycles, iron oxide cycles, tin oxide cycles, terbium oxide cycle, mixed ferrite cycles, ceria cycles, and perovskite cycles. In case of zinc and tin oxide cycles, due to the volatile nature of the MOs involved, the loss of reactive material due to high-temperature operation is inevitable. In the case of the iron oxide, ferrite, ceria, and perovskite cycles, the complete reduction of the MOs is not possible, and hence lower amount of H2 production is expected. Therefore, it is highly essential to investigate new thermochemical cycles for H2 production via thermochemical water splitting. In this paper, the solar reactor efficiency analysis of metal oxide-based two-step solar thermochemical water splitting cycle was investigated in detail. Computational thermodynamic modeling of this cycle is performed (in two sections) using commercial thermodynamic HSC Chemistry software and databases. In section one, the thermodynamic equilibrium compositions during the solar thermal reduction and oxidation via water splitting were determined. In section two, an energy and exergy analysis of the metal oxide cycle was carried out. The solar reactor absorption efficiency, the required solar energy input, radiation heat losses, the rate of heat rejected by the quench unit and the water-splitting reactor, and the solar-to-fuel conversion efficiency of the metal oxide cycle were determined via computational thermodynamic modeling and the results reported.