Abstract
Due to the requirement to develop carbon-free energy, solar energy conversion into chemical energy carriers is a promising solution. Thermochemical fuel production cycles are particularly interesting because they can convert carbon dioxide or water into CO or H2 with concentrated solar energy as a high-temperature process heat source. This process further valorizes and upgrades carbon dioxide into valuable and storable fuels. Development of redox active catalysts is the key challenge for the success of thermochemical cycles for solar-driven H2O and CO2 splitting. Ultimately, the achievement of economically viable solar fuel production relies on increasing the attainable solar-to-fuel energy conversion efficiency. This necessitates the discovery of novel redox-active and thermally-stable materials able to split H2O and CO2 with both high-fuel productivities and chemical conversion rates. Perovskites have recently emerged as promising reactive materials for this application as they feature high non-stoichiometric oxygen exchange capacities and diffusion rates while maintaining their crystallographic structure during cycling over a wide range of operating conditions and reduction extents. This paper provides an overview of the best performing perovskite formulations considered in recent studies, with special focus on their non-stoichiometry extent, their ability to produce solar fuel with high yield and performance stability, and the different methods developed to study the reaction kinetics.
Highlights
World energy requirements are still increasing, and fossil fuels combustion contributes to global warming
Thermochemical redox cycles are promising for converting solar energy into chemical energy in the form of sustainable solar fuels that can be stored long-term, transported long-range, and used on-demand
Perovskites represent a promising class of materials for thermochemical fuel production cycles
Summary
World energy requirements are still increasing, and fossil fuels combustion contributes to global warming. A solar-activated thermal reduction (TR) of the material at high temperature creates oxygen vacancies in the oxide lattice, producing O2 , as represented by the reaction (1). Improving the overall process efficiency requires increasing the fuel production yields and rates while decreasing the operating temperature to reduce heat losses. Ceria (CeO2 ) is able to maintain its crystal structure over a large range of non-stoichiometry and operating conditions It exhibits rapid reaction kinetics and fast oxygen diffusion rates, which promotes the reversible phase transitions between the oxidized and partially reduced states in a large range of non-stoichiometry. Perovskite-structured materials have emerged as promising candidate catalysts for high-temperature thermochemical fuel production [6]. The first section describes the redox system thermodynamics, the perovskite formulations that were studied in thermochemical cycles are summarized, and the methods used to study the perovskites redox reaction kinetics are described
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