Reversible Phase Transformations in Novel Ce‐Substituted Perovskite Oxide Composites for Solar Thermochemical Redox Splitting of CO<sub>2</sub>
J. Madhusudhan Naik, C. Ritter, Brendan Bulfin, Aldo Steinfeld, Rolf Erni, Greta R. Patzke
Abstract
Abstract Thermochemical splitting of CO 2 and H 2 O via two‐step metal oxide redox cycles offers a promising approach to produce solar fuels. Perovskite‐type oxides with the general formula ABO 3 have recently gained attention as an attractive redox material alternative to the state‐of‐the‐art ceria, due to their high structural and thermodynamic tunability. A novel Ce‐substituted lanthanum strontium manganite perovskite‐oxide composite, La 3+ 0.48 Sr 2+ 0.52 (Ce 4+ 0.06 Mn 3+ 0.79 )O 2.55 (LSC25M75) is introduced, aiming to bridge the gap between ceria and perovskite oxide‐based materials by overcoming their individual thermodynamic constraints. Thermochemical CO 2 splitting redox cyclability of LSC25M75 evaluated with a thermogravimetric analyzer and an infrared furnace reactor over 100 consecutive redox cycles demonstrates a twofold higher conversion extent to CO than one of the best Mn‐based perovskite oxides, La 0.60 Sr 0.40 MnO 3 . Based on complementary in situ high temperature neutron, synchrotron X‐ray, and electron diffraction experiments, unprecedented structural and mechanistic insight is obtained into thermochemical perovskite oxide materials. A novel CO 2 splitting reaction mechanism is presented, involving reversible temperature induced phase transitions from the n = 1 Ruddlesden–Popper phase (Sr 1.10 La 0.64 Ce 0.26 )MnO 3.88 ( I4/mmm , K 2 NiF 4 ‐type) at reduction temperature (1350 °C) to the n = 2 Ruddlesden–Popper phase (Sr 2.60 La 0.22 Ce 0.18 )Mn 2 O 6.6 ( I4/mmm , Sr 3 Ti 2 O 7 ‐type) at re‐oxidation temperature (1000 °C) after the CO 2 splitting step.