| Abstract Scope |
Perovskite oxides are promising alternatives to state-of-the-art fluorite CeO2-δ in solar-driven thermochemical fuel production. Guided by computational insights, we explore the thermodynamic properties and water splitting efficacy of the perovskites SrTi0.5Mn0.5O3-δ (STM55) and CaTi0.5Mn0.5O3-δ (CTM55). While STM55 is cubic structure under all accessible values of oxygen non-stoichiometry (δ), CTM55 has an orthorhombic structure at small δ, and transforms to a cubic phase when δ ≥ 0.022. The cubic phases of both materials provide attractive combinations of moderate enthalpy, 200 – 250 kJ (mol-O)-1, and high entropy, ~ 150 J (mol-O)-1 K-1 at δ = 0.1. Using a water splitting cycle in which the materials are reduced at just 1350 °C (pO2, ~10-5 atm), remarkable hydrogen yields of 10 mL g-1 and 7.4 mL g-1 are achieved, respectively, for CTM55 and STM55. Comparison of the measured gas production profiles to those predicted for quasi-equilibrium behavior suggests that under most conditions, the fuel production rate is largely limited by thermodynamic rather than kinetic constraints. |