The thermodynamic and defect chemical opportunities and challenges of perovskite oxides used for thermochemical water and carbon dioxide splitting are reviewed.

Carbon dioxide capture and mitigation form a key part of the technological response to combat climate change and reduce CO2 emissions. Solid materials capable of reversibly absorbing CO2 have been the focus of intense research for the past two decades, with promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this review, we explore the fundamental aspects underpinning solid CO2 sorbents based on alkali and alkaline earth metal oxides operating at medium to high temperature: how their structure, chemical composition, and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines, including materials discovery, synthesis, and in situ characterization, to present a coherent understanding of the mechanisms of CO2 absorption both at surfaces and within solid materials.

Understanding 'electro-chemo-mechanics' in oxygen ion conducting membranes represents a foundational step towards new energy devices such as micro fuel cells and oxygen or fuel separation membranes. For ionic transport in macro crystalline electrolytes, doping is conventionally used to affect oxygen ionic association/migration energies. Recently, tuning ionic transport in films through lattice strain conveyed by substrates or heterostructures has generated much interest. However, reliable manipulation of strain states to twist the ionic conduction in real micro energy devices remains intractable. Here, we demonstrate that the oxygen ionic conductivity clearly correlates with the compressive strain energy acting on the near order of the electrolyte lattices by comparing thin-film ceria-based membrane devices against substrate-supported flat structures. It is possible to capitalize on this phenomenon with a smart choice of strain patterns achieved through microelectrode design. We highlight the importance of electro-chemo-mechanics in the electrolyte material for the next generation of solid-state energy conversion microdevices.

Storing abundant solar energy in synthetic fuels is key to ensure a sustainable energy future by replacing fossil fuels and reduce global warming emissions. Practical implementation of the solar-to-fuel technology is predicated on finding new materials with higher efficiency and lower operation temperature than state-of-the-art. We use criteria aimed for designing such efficient solar-to-fuel conversion materials in the perovskite system. Based on thermodynamic considerations first perovskite solute-solution series, La 0.6 Sr 0.4 Cr 1-x Co x O 3-δ , are investigated to gain fundamental understanding on the role of B-site cationic doping towards water and CO 2 splitting to synthetic fuel. Notably, all of the novel material compositions operate in a strongly lowered temperature regime of 800-1200 ˚C compared towards state-of-the-art binary oxides in the field. We find an optimum in doping for fuel 2 production performance, namely La 0.6 Sr 0.4 Cr 0.8 Co 0.2 O 3-δ which viably splits both CO 2 and H 2 O. Based on thermogravimetric analysis, we show that highest performing perovskite splits 25 times more CO 2 compared to the current state-of-the-art material, ceria, for two-step thermochemical cycling 800-1200 ˚C. No adverse formation of carbonates in CO 2 atmosphere or cation segregation were observed in near and long range structural investigations, which highlight the durability and potential of these solid solutions. These new perovskite compositions enable lowering of the standard solar-to-fuel reactor temperature by 300°C. Lowered operating temperature has tremendous implications for solarsynthesized fuels in a reactor in terms of lowered heat loss, increased efficiency, and reactor materials.