Development of iron-nickel containing perovskites with increased oxygen carrier capacity for chemical looping H₂ production

Modifications of the perovskite La_0.6Sr_0.4FeO_3-δ (LSF) using different amount of Ni replacing Fe in the LSF lattice have been synthesised, tested and fully characterised under cyclic redox conditions in the temperature range of 600–900 °C. The results are compared with reference LSF material in terms of material and process performance. X-ray diffraction characterisation results showed that the increase of Ni content leads to the general formation of La_xSr_1-xFe_yNi_1-yO₃ species; at higher Ni doping, the formation of multiple perovskite species, and the formation of Ruddlesden-popper perovskite (La_0.3Sr_0.7)₂FeO₄. The best performance of cyclic stability was achieved with La_0.6Sr_0.4Ni_0.33Fe_0.67O_3-δ exhibiting only a 3 % capacity drop over 20 cycles, while a larger drop in capacity (33 % for La_0.6Sr_0.4Ni_0.5Fe_0.5O_3-δ and 6 % for La_0.6Sr_0.4Ni_0.1Fe_0.69O_3-δ) was obtained with other materials due to structural breakdown, sintering, and carbon deposition. Overall, an increase of 4.5 times of oxygen carrier capacity was recorded compared to La_0.6Sr_0.4FeO₃ during oxidation with steam, resulting in 0.96 mmolH₂/g_oc hydrogen yield at 900°C at a 55 % H₂O conversion. The total oxygen capacity increased with Ni doping due to structure modifications which increased the oxygen active sites available. In the case of reduction with CO, the same material did not show carbon deposition, sintering, or structural breakdown. Furthermore, long term stability has been confirmed by performing 100 redox cycles in a thermogravimetric analyser, with H₂ as the reducing agent.