A new highly oxygen-deficient and cubic Pr3ZrO8-δ for intermediate-temperature thermochemical production of oxygen and hydrogen

Two-step thermochemical cycles offer a clean route for hydrogen and oxygen production but are typically limited to high temperatures exceeding 1500 °C. Lowering operating temperatures would enable the use of alternative heat sources such as industrial waste heat. Here, we report Pr3ZrO8 as a new enabling material for efficient intermediate-temperature redox cycling, with thermal reduction at 900 °C in argon and steam oxidation at 400 °C. Pr3ZrO8 adopts a face-centered cubic structure similar to CeO2 but exhibits significantly greater oxygen deficiency, achieving average oxygen and hydrogen fluxes of 331.7 and 70.3 µmol·g-1, respectively, over ten cycles at 20%H₂O. These values surpass those of leading CeO2₋δ and perovskite oxides under comparable or more severe conditions. In-situ neutron and X-ray diffraction determine the phase stability boundaries of Pr3ZrO8, while density functional theory identifies O-H bond cleavage as the rate-limiting step. These results establish Pr3ZrO8 as a promising material for intermediate-temperature thermochemical oxygen and hydrogen production.