A Review of Solar Thermochemical CO2 Splitting Using Ceria-Based Ceramics With Designed Morphologies and Microstructures

Abstract

This review explores the advances in the synthesis of ceria materials with specific morphologies or porous macro- and microstructures for the solar-driven production of carbon monoxide (CO) from carbon dioxide (CO2). As the demand for renewable energy and fuels continues to grow, there is a great deal of interest in solar thermochemical fuel production (STFP), with the use of concentrated solar light to power the splitting of carbon dioxide. This can be achieved in a two-step cycle, involving the reduction of CeO2 at high temperatures, followed by oxidation at lower temperatures with CO2, splitting it to produce CO, driven by concentrated solar radiation obtained with concentrating solar technologies (CST) to provide the high reaction temperatures of typically up to 1,500°C. Since cerium oxide was first explored as a solar-driven redox material in 2006, and to specifically split CO2 in 2010, there has been an increasing interest in this material. The solar-to-fuel conversion efficiency is influenced by the material composition itself, but also by the material morphology that mostly determines the available surface area for solid/gas reactions (the material oxidation mechanism is mainly governed by surface reaction). The diffusion length and specific surface area affect, respectively, the reduction and oxidation steps. They both depend on the reactive material morphology that also substantially affects the reaction kinetics and heat and mass transport in the material. Accordingly, the main relevant options for materials shaping are summarized. We explore the effects of microstructure and porosity, and the exploitation of designed structures such as fibers, 3-DOM (three-dimensionally ordered macroporous) materials, reticulated and replicated foams, and the new area of biomimetic/biomorphous porous ceria redox materials produced from natural and sustainable templates such as wood or cork, also known as ecoceramics.

High performance cork-templated ceria for solar thermochemical hydrogen production via two-step water-splitting cycles

“…47 and this felt also produced superior results to CG17-like cork-derived ceria for thermochemical CO 2 splitting. 28 However, as discussed in a review of the effects of morphology on this process, 23 this was very much a dense 2D material of compressed fibres, and would be problematic to extend to a 3D structure to convert sizeable quantities of water to hydrogen. A considerable degradation of the CeO 2 after exposure to high-flux radiation was also observed.…”

“…In addition, ceria with morphologies that retain high specific surface area and interconnected micron-scale porosity allow for more rapid fuel production, as highlighted in a comprehensive review on the effect of designed morphologies and microstructures of ceria-based ceramics on the solar thermochemical CO 2 splitting process. 23 Three-dimensionally ordered macroporous (3-DOM) ceria, featuring both interconnected and ordered pores, was reported to increase the H 2 and CO production yields by 75% and 175%, respectively. 24 This was attributed to its enhanced surface area and its interconnected pore structure that facilitates the transport of reacting species to and from oxidation sites.…”

Solar Redox Cycling of Ceria Structures Based on Fiber Boards, Foams, and Biomimetic Cork-Derived Ecoceramics for Two-Step Thermochemical H2O and CO2 Splitting

“…The reduction step is affected by the diffusion length for lattice oxygen transfer, while the oxidation reaction largely depends on the porous structure and specific surface area of the material, since it is a surface-controlled solid/gas reaction. These two properties are impacted by the reactive material microstructure 32 , which is thus a key parameter for enhancing the thermochemical performance.…”

Constructing Hierarchical Porous Carbons With Interconnected Micro-mesopores for Enhanced CO2 Adsorption

“…In order to reduce the carbon dioxide content in the air, people began to develop new energy, such as hydrogen energy (Qi et al, 2019), degradation of pollutants and sewage (Sun et al, 2018;Chen et al, 2019), among others, but fundamentally solve the problem of carbon dioxide pollution. However, although carbon dioxide is considered as the main greenhouse gas, it is a transformable carbon resource (Garbarino et al, 2014;Son et al, 2014;Pullar et al, 2019). In the presence of a suitable catalyst, the captured carbon dioxide molecules can be converted into synthetic natural gas, such as methane (Lavoie, 2014;Wang et al, 2016;Xia et al, 2019).…”