(262j) Computational Thermodynamic Analysis of a Solar Thermochemical Manganese Oxide - Manganese Sulfate Water Splitting Cycle

In a long list of solar thermochemical water splitting cycles, the sulfur-iodine cycle (SI Cycle) and its variation the hybrid sulfur cycle are more appealing as the required operating temperatures are lower as compared to other thermochemical cycles. However, as sulfation poisoning is a major concern related to such reactions, simply the noble metal catalysts were observed to be active towards the endothermic dissociation of SO₃. The utilization of noble catalyst increases the cost of hydrogen production (due to limited availability and high cost) and hence these types of catalysts are less preferable. To solve this issue, we propose, a two-step hybrid metal oxide â?? metal sulfate water splitting cycle for the production of solar hydrogen. In particular, this investigation reports a two-step hybrid manganese oxide â?? manganese sulphate (MnOâ??MnS) water splitting cycle was thermodynamically investigated towards solar H₂ production. It is a two-step process in which the first solar step belongs to the endothermic thermal reduction of MnSO₄ into MnO, SO₂, and O₂. The exothermic step two corresponds to the non-solar oxidation of MnO by SO₂ and H₂O producing MnSO₄ and H₂. The equibrium thermodynamic compositions associated with both steps were determined by using HSC Chemistry thermodynamic software and databases. The variation of the reaction enthalpy, entropy and Gibbs free energy for the thermal reduction and water splitting steps with respect to the operating conditions were studied. Furthermore, solar absorption efficiency of the solar reactor, net energy required to operate the MnOâ??MnS cycle, solar energy input to the solar reactor, radiation heat losses from the solar reactor, rate of heat rejected to the surrounding from the water splitting reactor, and maximum theoretical solar energy conversion efficiency of the MnOâ??MnS cycle was determined by performing the exergy analysis by following the principles of second law of thermodynamic over different solar reactor temperatures and with/without considering the heat recuperation. Also, effect of inert carrier gas on solar to fuel conversion efficiency was examined. Findings of this investigation will be presented in detail.