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.