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Carbon Capture and Storage

A new area of research in the Grey group has focused on finding novel materials for carbon capture and storage (CCS). The work centres around a promising process to remove CO2 from post-combustion flue gases, known as carbonate looping, which uses a solid sorbent material (such as CaO) to chemically react with CO2 at high temperatures to form a solid carbonate phase. Cycling of this phase to a higher temperature leads to the decomposition of the carbonate, simultaneously releasing a pure CO2 gas stream and regenerating the original oxide material. While an optimised carbonate looping process promises to be more energy efficient than current technologies, the process suffers from the deterioration of CaO over many cycles of use, and subsequent loss in reactive capacity. Our work seeks to better understand the thermodynamics and reaction kinetics of the CaO system, as well as to devise a rational scheme to find alternative materials.

Our first step was to devise a high-throughput screening methodology to search for novel materials based on theoretical calculations (in collaboration with the Materials Project). This work identified 640 materials that could be potentially implemented in high temperature carbonate looping, a number of which had much lower predicted energy costs than the commonly used CaO. Subsequent characterisation of these promising materials found good agreement the results of the screening, validating this rational design approach to find new functional materials for CCS.

Perovskites are an attractive class of materials due to their capacity for chemical flexibility, allowing their physical properties to be fine-tuned. Previously it had not been possible to find a perovskite material that could be reversibly carbonated for use in CCS. Our research found that Ba4Sb2O9 (a 6H perovskite) was not only able to rapidly absorb CO2, even at room temperature, but that this absorption was fully reversible. Further cycling studies found that the combined absorption and regeneration reactions proceed without any significant reduction in the CO2 absorption capacity of the material, even after 100 cycles. These results represent the first time a perovskite material has been shown to have such a stable CO2 cycling capacity, and completely changes the chemical landscape that is available for the discovery of new CCS materials.

Fig. Schematic representation of the cycling of Ba4Sb2O9 for carbon capture.

We have also used solid-state nuclear magnetic resonance techniques to study how ion dynamics influence the CO2 absorption properties of alkali oxides. Using measurements collected up to the high operating temperatures of these CO2 capture materials, it was found that faster ionic motion that is activated with increasing temperature correlates with faster CO2 absorption, providing an insight into the underlying mechanism of CO2 capture in these materials.

List of selected publications:

"Large Scale Computational Screening and Experimental Discovery of Novel Materials for High Temperature CO2 Capture", MT Dunstan, A Jain, W Liu, SP Ong, T Liu, J Lee, KA Persson, SA Scott, JS Dennis and CP Grey, Energy Environ. Sci. (2016) 9, 1346. (DOI: 10.1039/c5ee03253a)

"In Situ Studies of Materials for High Temperature CO2 capture and Storage", MT Dunstan, SA Maugeri, W Liu, MG Tucker, OO Taiwo, B Gonzalez, PK Allan, MW Gaultois, PR Shearing, DA Keen, AE Philipps, MT Dove, SA Scott, JS Dennis and CP Grey, Faraday Discuss. (2016) 192, 217. (DOI: 10.1039/c6fd00047a)

"Reversible CO2 Absorption by the 6H Perovskite Ba4Sb2O9", MT Dunstan, W Liu, AF Pavan, JA Kimpton, CD Ling, SA Scott, JS Dennis and CP Grey, Chem. Mater. (2013) 25, 4881. (DOI: 10.1021/cm402875v)