Improving hydrogen yields, and hydrogen: Steam ratio in the chemical looping production of hydrogen using Ca₂Fe₂O₅

A thermodynamic property of Ca₂Fe₂O₅ was exploited to improve the efficiency of the steam-iron process to produce hydrogen. The ability of reduced Ca₂Fe₂O₅ to convert a higher fraction of steam to hydrogen than chemically unmodified Fe was demonstrated in a packed bed. At 1123 K, the use of Ca₂Fe₂O₅ achieved an equilibrium conversion of steam to hydrogen of 75%, in agreement with predicted thermodynamics and substantially higher than that theoretically achievable by iron oxide, viz. 62%. Furthermore, in Ca₂Fe₂O₅, the full oxidation from Fe(0) to Fe(III) can be utilised for hydrogen production - an improvement from the Fe to Fe₃O₄ transition for unmodified iron. Thermodynamic considerations demonstrated in this study allow for the rational design of oxygen carriers in the future. Modifications of reactors to capitalise on this new material are discussed.