BaCe0.25Mn0.75O3−δ—a promising perovskite-type oxide for solar thermochemical hydrogen production

Abstract

Solar-thermal based hydrogen production technologies employing two-step metal oxide water-splitting cycles are emerging as a viable approach to renewable and sustainable solar fuels. However, materials innovations that overcome thermodynamic constraints native to the current class of solar-thermal water splitting oxides are required to increase solar utilization and process efficiency. Lowering oxide thermal reduction temperature while maintaining high water-splitting favorability are important ways to enhance such performance metrics. Recent attention to perovskite-type oxides as an alternative to ceria, which is widely viewed as the state-of-the art redox material, is driven by demonstrated thermodynamic and structural tuning derived through engineered composition. Here we discuss the unique properties of BaCe_0.25Mn_0.75O₃ (BCM) within the context of thermochemical water splitting materials. Firstly, BCM is a novel example of a line compound with B-site substitution of Mn by Ce. It also exhibits a polymorph phase transition during thermal reduction and yields nearly 3× more H₂ than ceria when reduced at lower temperature (1350 °C). More importantly, BCM exhibits faster oxidation kinetics and higher water-splitting favorability than Sr_xLa_1−xMn_yAl_1−yO₃ (x, y = 0.4, 0.6), which is a well-studied and popular Mn-based perovskite formulation. The unique properties manifested by BCM through engineered composition offer new pathways towards unlocking higher performing materials for solar thermochemical water splitting.