Computational Discovery of Metal Oxides for Chemical Looping Hydrogen Production

Abstract

Chemical looping hydrogen production (CLH) that uses methane and water as feedstock is a promising pathway that can offer both the use of renewable resources as well as efficient CO2 capture capabilities. Here, we utilized CALculation of PHAse Diagrams (CALPHAD) thermodynamic database to study the water conversion efficiency of metal oxides (MOx) for CLH. We report the discovery of new oxides with theoretical hydrogen yields up to 8 times higher compared to state-of-the-art oxides such as ceria and ferrites. Results show that oxygen capacity in these oxides is a non-monotonic function of iron concentration, a prediction that has been experimentally verified and yielded an optimal concentration. More specifically, Fe0.40Co0.60Ox was found to be the optimal stoichiometry with the largest water conversion efficiency capability at >50% at 700°C. A technoeconomic model quantified the importance of MOx oxygen capacity and water conversion efficiency in this process, but also shed light into the great potential of chemical looping hydrogen production with a hydrogen cost of $1.32 ± 0.40 per kg at a scale of 90 tons per day. This is comparable to steam methane reforming (SMR), but with the added benefit of producing pure CO2, and thereby eliminating the cost of CO2 separation prevalent in SMR. Sensitivity analysis on key variables such as cycle time, oxygen capacity and oxide lifetime allowed quantification of their effect in the final unit cost of H2.