High-capacity thermochemical CO₂ dissociation using iron-poor ferrites

Abstract

Dissociation of CO2 to form CO can play a key role in decarbonizing our energy system. Fe-poor ferrites exhibit significantly higher capacity for thermochemical CO2 dissociation than state-of-the-art materials such as ceria and perovskites.

Thermodynamic guiding principles of high-capacity phase transformation materials for splitting H2O and CO2 by thermochemical looping

“…S1–S2, Table S1, and Subsections 1–4 in Supplementary Text of ESI†). The thermodynamic requirements for reactions (1)/(3) and (4) to proceed are: 51 where p O2 is the (equivalent) oxygen partial pressure during thermal or chemical reduction and…”

“…1C and D can still give a relatively accurate estimation of thermodynamic equilibrium CO 2 splitting capacity, as often seen in published van't Hoff analyses. 44,51 In general, for a material whose dots are dense in the thermodynamically feasible zone, its h O and s O properties remain feasible for the two-step cycle across a large range of x , leading to a large thermodynamic equilibrium CO 2 splitting capacity. The density of dots between 1 and 4 and between 2 and 3 is higher for Fe 0.45 Co 0.55 O x 1 than for Fe 2/3 Co 1/3 O x 2 , and therefore, Fe 0.45 Co 0.55 O x 1 has a higher oxygen exchange capacity because of a larger range of x , giving a larger total entropy of reduction.…”

“…Recently, iron(Fe)-poor ferrite (Fe y M 1− y O x where y < 2/3) was found to have a counterintuitively high capacity of CO 2 splitting compared to the traditional Fe-rich ferrites ( y ≥ 2/3) in the two-step thermochemical cycle (with thermal reduction), though Fe is the redox active element. 51 Even more recently, in the case of thermochemical looping hydrogen production with chemical reduction, various Fe-poor ferrites were shown to have much higher capacity and water-to-H 2 conversion compared to the benchmark material, Fe 3 O 4 –FeO–Fe. 52 Technoeconomic analysis suggests that such Fe-poor ferrites offer the promising prospect of thermochemical looping H 2 production at <$2 per kg-H 2 .…”

“…53–55 Van't Hoff analysis was conducted on these ferrites to derive h O and s O . 51 However, the fundamental reasons that cause the counterintuitive dependence of CO 2 splitting capacity on the Fe ratio remain unidentified.…”

Reversible Phase Transformations in Novel Ce‐Substituted Perovskite Oxide Composites for Solar Thermochemical Redox Splitting of CO2

“…reported that La 0.6 Sr 0.4 MnO 3‐ δ perovskites have a critical CO 2 :CO conversion ratio of 650:1 at T red = 1300 °C and p O 2 = 10 −5 atm, and T oxi = 800 °C indicating a very low conversion extent and using a lower CO 2 molar gas flow rate than critical (CO 2 :CO) ratio would result in negligible or zero CO yield. [ 51 ]…”