Abstract
The computational thermodynamic analysis of a samarium oxide-based two-step solar thermochemical water splitting cycle is reported. The analysis is performed using HSC chemistry software and databases. The first (solar-based) step drives the thermal reduction of Sm2O3 into Sm and O2. The second (non-solar) step corresponds to the production of H2 via a water splitting reaction and the oxidation of Sm to Sm2O3. The equilibrium thermodynamic compositions related to the thermal reduction and water splitting steps are determined. The effect of oxygen partial pressure in the inert flushing gas on the thermal reduction temperature (TH) is examined. An analysis based on the second law of thermodynamics is performed to determine the cycle efficiency (ηcycle) and solar-to-fuel energy conversion efficiency (ηsolar−to−fuel) attainable with and without heat recuperation. The results indicate that ηcycle and ηsolar−to−fuel both increase with decreasing TH, due to the reduction in oxygen partial pressure in the inert flushing gas. Furthermore, the recuperation of heat for the operation of the cycle significantly improves the solar reactor efficiency. For instance, in the case where TH = 2280 K, ηcycle = 24.4% and ηsolar−to−fuel = 29.5% (without heat recuperation), while ηcycle = 31.3% and ηsolar−to−fuel = 37.8% (with 40% heat recuperation).
Highlights
Two concerns in many countries are long-term shortages of fossil fuels and the need to secure fuel supplies
The main reactions involved in the metal oxide (MO) based two‐step solar thermochemical water splitting
HSC simulation results indicate that the temperature (TH ) required for complete thermal reduction of Sm2 O3 can be significantly decreased with a reduction in the oxygen partial pressure in the inert flushing gas used inside the reactor
Summary
Two concerns in many countries are long-term shortages of fossil fuels and the need to secure fuel supplies. 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 [2,3,4]. Two-step solar thermochemical water splitting cycle are as follows: thermal energy viathermal water splitting reactions. 1: Solar dissociation of MO: advantages include a high energy density (on a mass basis) and non‐polluting nature. The main reactions involved in the MO based two‐step solar thermochemical water splitting
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