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. We report here a two-step thermochemical cycle using a variety of iron-poor (Fe-poor) ferrites (Fe_yM_1−yO_x where y < 2/3) that produce CO with unusually high yield using Fe as the redox active species. Conventional wisdom suggests that increasing the Fe fraction would increase the capacity for CO₂ dissociation. Here, we report the opposite result: at partial pressure ratio CO : CO₂ = 1 : 100, we demonstrated CO yields of 8.0 ± 1.0 mL-CO per gram from Fe_0.35Ni_0.65O_x, and 3.7 ± 1.0 mL-CO per gram from Fe_0.45Co_0.55O_x, at a thermal reduction temperature of 1300 °C; remarkably, these CO₂ dissociation capacities are significantly higher than those of state-of-the-art materials such as spinel ferrites (Fe₂MO₄), (substituted) ceria, and Mn-based perovskite oxides. Optimization of the kinetics of Fe-poor ferrites with a ZrO₂ support resulted in higher CO yields per gram of ferrite. The unexpected CO yield vs. Fe ratio trend is consistent with the prediction of calculated ternary phase diagrams, which suggest a swing between spinel and rocksalt phases. These Fe-poor ferrites open new opportunities for tuning the redox properties of oxygen exchange materials.