Published at the Journal of Physical Chemistry – Solar Thermochemical Redox Cycling Using Ga- and Al-Doped LSM Perovskites for Renewable Hydrogen Production

Abstract
Solar thermochemical hydrogen production using redox-active metal oxides is a promising pathway for the production of green hydrogen and synthetic fuel precursors. Herein, the perovskite material (La_0.6Sr_0.4)_0.95Mn_0.8Ga_0.2O_3−δ (LSMG6482) is identified as a promising metal oxide for thermochemical water splitting. LSMG6482, along with more-established water splitters ceria and (La_0.6Sr_0.4)_0.95Mn_xAl_1–xO_3−δ (LSMA) perovskites, is experimentally characterized via thermogravimetric (TGA) analysis and high-temperature water splitting in a reactor simulating solar concentrating conditions. TGA analysis demonstrated that LSMG6482 has high and stable oxygen exchange capacity under controlled pO₂ redox cycling, demonstrated by large changes in oxygen nonstoichiometry (δ) relative to ceria. Water splitting experiments using laser heating (T_red = 1400 °C, T_ox = 1200 °C) resulted in H₂ yields of 165.1 μmol g^–1 for the candidate LSMG6482 composition, exceeding that of all benchmark materials tested. Under high conversion oxidation conditions, where H₂ is cointroduced with H₂O (150 ≤ nH₂O/nH₂ ≤ 500), H₂ yields were greatest for LSMG6482 and LSMA6482, up to four times that of ceria at the highest nH₂O/nH₂ conditions. Crystallographic analysis showed that over the course of experimentation, there is some secondary phase growth for all perovskite compositions, except for LSMA6482, but there was no observable degradation in H₂ yields.

DOI: 10.1021/acs.jpcc.4c02797