Carbon dioxide capture and storage technologies are short to mid-term solutions to reduce anthropogenic CO 2 emissions. CaO-based sorbents have emerged as a viable class of costefficient CO 2 sorbents for high temperature applications. Yet, CaO-based sorbents are prone to deactivation over repeated CO 2 capture and regeneration cycles. Various strategies have been proposed to improve their cyclic stability and rate of CO 2 uptake including the addition of promoters and stabilizers (e. g., alkali metal salts and metal oxides), as well as nano-structuring approaches. However, our fundamental understanding of the underlying mechanisms through which promoters or stabilizers affect the performance of the sorbents is limited. With the recent application of advanced characterization techniques, new insight into the structural and morphological changes that occur during CO 2 uptake and regeneration has been obtained. This review summarizes recent advances that have improved our mechanistic understanding of CaO-based CO 2 sorbents with and without the addition of stabilizers and/or promoters, with a specific emphasis on the application of advanced characterization techniques.

Efficient operation is crucial for the deployment of photoelectrochemical CO2 reduction devices for large-scale artificial photosynthesis. In these devices, undesired transport of CO2 reduction products from the reduction electrode to the oxidation electrode may occur through a liquid electrolyte and an ion exchange membrane, reducing device productivity and increasing the energy required for product purification. Our work investigated the CO2 reduction product crossover through ion exchange membranes separating the cathode and anode compartments in CO2 reduction cells. The concentrations of liquid products produced by CO2 reduction on copper foil were measured. A systematic approach for the investigation of product crossover was developed. The crossover of products was analyzed over a range of working electrode potentials (−1.08 V vs RHE to −0.88 V vs RHE) in cells employing a commercial Selemion AMV membrane and a new poly­(vinylimidazolium) family of ion exchange membranes with variable chemical and structural properties. We found that product loss due to electromigration of charged species in the device was more significant than product loss due to diffusion of uncharged species. To reduce the crossover of CO2 reduction products, the influence of membrane properties such as the ionic conductivity and water volume fraction was investigated for the Selemion AMV membrane and poly­(vinylimidazolium) membranes with variable material properties. We show that the water volume fraction and, by extension, ionic conductivity of the membrane may be controlled to reduce product crossover in CO2 reduction artificial photosynthesis devices.

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