Compositionally Complex Perovskite Oxides for Solar Thermochemical Water Splitting

Solar thermochemical hydrogen (STCH) generation is a promising approach for eco-friendly H₂ production, but conventional STCH redox compounds cannot easily achieve desirable thermodynamic and kinetic properties and phase stability simultaneously due to a rather limited compositional space. Expanding from the nascent high-entropy ceramics field, this study explores a new class of compositionally complex perovskite oxides (La_0.8Sr_0.2)(Mn_(1–x)/3Fe_(1–x)/3Co_xAl_(1–x)/3)O₃ with new non-equimolar designs for STCH. In situ X-ray photoelectron spectroscopy shows preferential redox of Co. The extent of reduction increases, but the intrinsic kinetics decreases, with increasing Co content. Consequently, (La_0.8Sr_0.2)(Mn_0.2Fe_0.2Co_0.4Al_0.2)O₃ achieves an optimal thermodynamic and kinetic balance. The combination of a moderate enthalpy of reduction, a high entropy of reduction, and preferable surface oxygen exchange kinetics enables a maximum H₂ production of 89.97 mmol mol_oxide^–1 in a short 1 h redox duration. Entropy stabilization may contribute to the phase stability during redox cycling without phase transformation, which enables STCH production for >50 cycles under harsh interrupted conditions. The underlying redox mechanism is further elucidated by a density functional theory-based parallel Monte Carlo computation approach. This study suggests a new class of non-equimolar compositionally complex ceramics for STCH and thermochemical looping.