CoFe ₂O ₄ on a porous Al ₂O ₃ nanostructure for solar thermochemical CO ₂ splitting

Projected growth in global population and continued industrialization of developing countries will increase total world energy consumption by 50% between 2008 and 2035 (U.S. Energy Information Administration (EIA), International Energy Outlook, DOE/EIA-0484(2011) (Washington, DC, September 2011)). This demand for energy will be largely met by burning more fossil fuels, thereby increasing anthropogenic carbon in the atmosphere and further fuelling geopolitical conflicts over control of dwindling energy resources. Recycling CO ₂ by splitting it in a solar-based thermochemical process is an attractive solution to both of these 21 ^st century problems. In this communication, we examine a novel chemistry for a two-step, non-volatile metal oxide CO ₂ splitting cycle that shuttles iron oxidation states (Fe ^2+/3+) between CoFe ₂O ₄ and FeAl ₂O ₄ spinel compounds within a nano-engineered material. This chemistry is dramatically different than current metal oxide cycles that exploit oxygen non-stoichiometry in ceria or solid solution behaviour in ferrites. The engineered material was prepared using atomic layer deposition and maintained structural integrity over 6 heating cycles under conditions that mimic a concentrated solar power application, namely an oxidation temperature of 1000 °C, reduction at 1460°C, and a heating rate of 16°C s ^-1 from low to high temperature. Oxygen uptake and release behaviour was similar to that of ceria. Raman spectroscopy was used to verify cycle chemistry.