Perovskite oxides - a review on a versatile material class for solar-to-fuel conversion processes

Thermochemical water and carbon dioxide splitting with concentrated solar energy is a technology for converting renewable solar energy into liquid hydrocarbon fuels as an alternative to fossil fuels, which are dominating in today's energy mix. For the conversion reaction to be efficient, special redox materials are necessary to perform the necessary chemical reactions in a thermochemical cycle. Through this review we carefully examine perovskite oxides to design and optimize next generation solar-to-fuel conversion materials operating on thermochemical cycles. To date efforts have primarily been directed to binary oxides among which most prominently ceria was selected. Despite the promise, ceria has an unfavorable high reduction temperature and is restricted in its opportunities to manipulate through extrinsic doping the oxygen nonstoichiometry and thermodynamic properties for oxygen exchange towards H2O and CO2 splitting. In contrast, recent reports highlight new opportunities to use and alter perovskite oxides in terms of elemental composition over a wider range to affect reduction temperature, oxygen exchange characteristics needed in the catalytic reactions and fuel yield. To further foster perovskites for solar-to-fuel conversion, we review basic concepts such as the lattice structure and defect thermodynamics towards CO2 and water splitting, discuss the role of oxygen vacancies and present strategies for an efficient search for new perovskite compositions. Summarizing, recent efforts on perovskite oxide compositions investigated are based on Fe, Mn, Co, or Cr with reported fuel yields of up to several hundred mmol per g per cycle in the literature. This article reviews the underlying principles, the latest advances and future prospects of perovskite oxides for solar-to-fuel technology.