Reversible Exsolution of Dopant Improves the Performance of Ca2Fe2O5 for Chemical Looping Hydrogen Production.

Hydrogen (H2) is a clean energy carrier and a major industrial feedstock, e.g., to produce ammonia and methanol. High-purity H2 can be produced efficiently from methane (CH4) using chemical looping-based approaches. In this work, we report on the development of a calcium-iron-based oxygen carrier (Ca2Fe2O5) doped with Ni or Cu and investigate its redox performance for H2 production when CH4 is used as the fuel. The experimental results suggest that the rapid formation of metallic Ni or Cu through exsolution promotes the reducibility of Ca2Fe2O5 with CH4. It was found that the reversible exsolution of Ni or Cu nanoparticles and their reincorporation in the Ca2Fe2O5 structure is key to avoid particle sintering and deactivation. Having the potential of converting a larger fraction of steam to H2 than pure iron oxide in addition to its higher reactivity with CH4, the doped calcium-iron-based oxygen carrier is a promising material for chemical looping H2 production.