| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Energy Harvesting & Storage | Monday Sessions |
| Session EH-MoE |
| Session: | Process |
| Presenter: | Ryan Richards, Colorado School of Mines, USA |
| Authors: | R.M. Richards, Colorado School of Mines, USA S. Shulda, National Renewable Energy Laboratory, USA G.A. Mutch, Newcastle University J.A. Anderson, University of Aberdeen D. Vega-Maza, University of Aberdeen |
| Correspondent: | Click to Email |
Carbon capture, utilisation and storage is a portfolio of processes to combat climate change. The capacity of sorbents proposed for low temperature carbon capture is entirely limited to surface interaction, resulting in a race to produce ever increasing surface areas - exemplified by metal-organic frameworks.
Metal oxides have a diverse range of electronic and physical properties that make them useful for a variety of applications such as semiconductors in diodes, electro- and thermo-chromics, catalysis and Li ion batteries --to name a few. One of the simplest structures of metal oxides is the rock-salt structure that are face-centered cubic crystals with the metal ion surrounded by six nearest-neighbor oxygen ions and vice versa. Amongst the rock-salt metal oxides, MgO is the most widely studied and is the second most abundant compound in the Earth’s crust at 35% (behind silica which is 42%). 1 Due to surface area reduction by sintering, solid metal oxides generally exhibit reduced adsorption capacity for carbon capture following high temperature exposure.
The preponderance of literature studies involving the properties of metal oxides has been conducted on the (100) surface because this surface is the most readily obtained and most thermodynamically stable form for most rock-salt metal oxides. The (100) surface is a checkerboard of alternating metal cations and oxygen anions. While most methods produce materials dominated by (100) surfaces, decomposition of metal hydroxides such as Mg(OH)2can initially yield materials with hydroxylated (111) surfaces via topotactic dehydration. 1-3 Following the development of techniques that allow for the deliberate preparation of materials with primarily (110) and (111) surfaces, came interest in potentially new properties of these surfaces. 4, 5
The (111) facet of MgO however, exhibits a high concentration of low coordinate sites. 4, 5 In recent work, MgO(111) nanosheets displayed high capacity for CO2, as well as a ≈ 65% increase in capacity despite a ≈ 30% reduction in surface area following sintering (0.77 mmol g-1@ 227 m2g-1vs 1.28 mmol g-1@ 154 m2g-1). 6 These results, unique to MgO(111) suggest intrinsic differences in the effects of sintering on basic site retention. Spectroscopic and computational investigations provided a new structure-activity insight; the importance of high temperature activation to unleash the capacity of the polar (111) facet of MgO. In summary, we present the first example of a faceted sorbent for carbon capture and challenge the assumption that sintering is necessarily a negative process; here we leverage high temperature conditions for facet-dependent surface activation.