Ternary Mixed Spinel Oxides as Oxygen Carriers for Chemical Looping Hydrogen Production Operating at 550 °C

Operating chemical looping at moderate temperatures circumvents the issue that the sintering of oxygen carrier materials is serious at typical operating conditions, 800-950 °C. However, lower temperatures can lead to deterioration on the reaction kinetics and thereby the low H₂ production rate and yield. Here, we present several doped spinel oxides consisting of earth-abundant elements for chemical looping water splitting. By virtue of the ability of the Cu dopant to improve the reduction of the Co-based binary spinel, the high reducibility of the dopants in the reduction period, as well as the phase reversibility in the water splitting period, Cu_0.25Co_0.25Fe_2.5O shows a high hydrogen yield (∼11.9 mmol g^-1) and an average hydrogen production rate (∼137.7 μmol g^-1 min^-1) at 550 °C, with negligible decays in repetitive redox cycles. The performance of this material is comparable to that of the state-of-the-art perovskites which usually contain rare-earth metals, enabling its potential in industrial implementation.