Enhancement effects of dopants and SiO2 support on mixed metal ferrites based two-step thermochemical water splitting

Abstract

Ferrites have emerged as potential materials in thermochemical fuel production due to its appreciated thermodynamic driving force of H2O/CO2 splitting and inexpensive. Herein, to enhance the utility of iron element and fuel release rate/production, dopants (such as Co, Mn, Sr, and Ce) and SiO2 support are used to improve the reactivity of LaFeO3/SiO2 derived two-step thermochemical water splitting (TCWS). It was found that the pure LaFeO3 perovskite shown negligible TCWS reactivity; cobalt doped into the structure of LaFeO3 could result in enhanced but limited utility of oxygen vacancy. Compared with unsupported LaFeO3, the actual redox phases of SiO2 supported samples are doped iron silicon oxides, (M,Fe)3-xSixO4 (M=dopants); the normalized molar iron based O2 production (mL per mmol of Fe) is increased by 5-fold for LaFeO3 (25wt%)/SiO2 and is further increased by 10 times for LaFe0.8Co0.2O3 (25wt%)/SiO2. It suggests that SiO2 support is helpful to disperse iron silicon oxides and alleviate sintering at high temperatures. XPS results reveal that the LaFeO3/SiO2 derived TCWS is driven by a repeated Fe2+/Fe3+ redox cycle and the utility of iron element is enhanced via the addition of cobalt dopant and SiO2 support. The cycle performance of LaFe0.8Co0.2O3 (25wt%)/SiO2 demonstrated that ∼2.8mLO2g−1material and ∼4.2mLH2g−1material were stably released when the TCWS was operated between 1350°C and 1100°C. The total mass based O2 and H2 productions of LaFe0.8Co0.2O3 (50wt%)/SiO2 can be further increased to ~4.5 and ~7.8mLg−1material, respectively.