Thermochemical gas reduction process using poly-cation oxide

A two-step thermochemical gas reduction process comprising repeatedly cycling a thermal reduction step and a gas reduction step;

• wherein the thermal reduction step comprises heating a poly-cation oxide under a reduced partial oxygen pressure, producing a reduced poly-cation oxide and oxygen gas;
• wherein the gas reduction step comprises reacting the reduced poly-cation oxide with a first gas to produce a second gas and reoxidized poly-cation oxide, wherein the first gas is reduced into the second gas;
• wherein the poly-cation oxide has at least two distinct crystal structures at two distinct temperatures corresponding to two distinct average oxidation states of at least one transition metal in a transformation between the poly-cation oxide and the reduced poly-cation oxide;
• wherein the poly-cation oxide is selected from the group consisting of
• a) an equimolar mixture of MgO, CoO, NiO, FeO and ZnO,
• b) (MgFeCoNi)0.8Li0.1Ga0.1Ox,
• c) (LiMgFeCoNi)Ox,
• d) (MgAlFeCoNi)Ox,
• e) (MgTiMnCoNi)0.75Fe0.25Ox,
• f) (MgMnCoNi)0.75Fe0.25Ox,
• g) (MgFeCoNiZn)O, and
• h) (MgFeCoNiCe)Ox(CoNi)0.65Fe0.35Ox,
• where compositions in parentheses correspond to equimolar concentrations, and where x is an appropriately chosen constant.