A promising route toward renewable fuel production is thermochemical splitting of carbon dioxide or water to produce carbon monoxide or hydrogen using concentrated solar energy. To carry out this reaction at practical temperatures, two-step reactions using metal oxides, including ceria, are employed. These heterogeneous reactions benefit from having large accessible surfaces and short diffusion paths within the structure of ceria. Such features can be achieved by hard templating methods. Here, we describe methods to tailor internal and external morphology of templated metal oxides for enhanced performance in two-step thermochemical reactions. In particular, we will consider porous ceria and doped ceria materials prepared by colloidal crystal (CC) templating and wood templating. Both methods produce highly interconnected pore systems with increased surface areas compared to nonporous active materials. In addition to controlling the internal pore architecture of the materials through the hard template, we employ polymerization-induced phase separation to alter the external morphology of ceria and other metal oxides, producing porous microspheres, hollow particles, porous sheet structures, or materials with hierarchical porosity. The predominant controlling factor of microstructural evolution in these syntheses is the degree of polymerization of the gel, which is controlled through tailoring reagent imbalance. We will describe the effects of structural morphology on carbon dioxide splitting, including effects on cycle kinetics and thermal stability of the porous materials. Ceria materials prepared by both CC templating and wood templating are capable of enhancing the kinetics of thermochemical CO production compared to nonstructured ceria. Whereas the CC-templated materials provide higher surface areas and greater peak production rates, wood-templated structures exhibit greater thermal stability and permit cycling at higher temperatures. Rapid cycling rates are feasible in these materials to increase the production of fuel over a given period of time.

Tailoring the structure of active materials for solar thermochemical fuel production through templating

249th National Meeting (2015)

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