(364f) Development of Capacity-Enhanced Oxygen Carriers for Chemical Looping Combustion By Exploiting Solid Solution Systems

Chemical looping combustion (CLC) is one of the most cost-effective solutions for producing affordable low carbon electricity. Oxygen carrying capacity is a key performance indicator determining the efficiency of chemical looping combustion (CLC). Amongst all 3d transition metal oxides, iron oxides are the cheapest option for chemical looping combustion. However, the oxygen carrying capacity of unmodified Fe₂O₃/Fe₃O₄ is low due to the stability of the Fe₃O₄ inverse spinel. This thermodynamic inevitability remains a great challenge to developing high capacity and stable Fe-based oxygen carriers. Here, we used the Calculation of Phase Diagrams (CALPHAD) method and designed xMgO⸱Fe₂O₃ oxygen carriers (x = 2, 4, or 6). By exploiting the MgO-Fe-O system (shown in Figure 1 left), in which two solid solutions may form, viz. Mg_1-xFe_xO and Mg_1−yFe_2+yO₄, we show that the capacity of Fe-based oxygen carriers can be substantially enhanced, from 1.08 mmol/g for Fe₂O₃ to >1.2 mmol/g solid, despite the fact that up to 60% of the oxygen carrier is inert MgO. Amongst the xMgO⸱Fe₂O₃ oxygen carriers, 6MgO⸱Fe₂O₃ shows the most stable performance over 100 cycles (see Figure 1 right) at 850 °C using CO₂/CO (molar ratio = 9:1, N₂ balance) as the fuel. We also investigated the nature of the FeO_x active centres over CLC cycles using complementary characterisation techniques. This study demonstrates the exploitation of solid solution system as a powerful tool for the design of high performance oxygen carriers.