In recent decades, the demand for energy has led to a significant increase in greenhouse gas emissions, mainly from burning fossil fuels such as coal, natural gas, and petroleum oils. These fuels emit large quantities of greenhouse gases and are limited and non-renewable, prompting the search for clean and sustainable energy sources . One promising alternative is hydrogen, a clean and renewable energy carrier that emits no harmful greenhouse gases while combustion . It can be produced from various feedstocks, including water, through indirect watersplitting methods . The Iodine-Sulfur (IS) cycle is a non-carbon thermochemical cycle with a high reported efficiency of ~51% for hydrogen production . This process consists of three reactions, including the Bunsen reaction, sulfuric acid decomposition, and hydroiodide decomposition . The thermochemical decomposition of sulfuric acid is a highly endothermic and corrosive reaction with a large kinetic barrier . It is a two-step reaction. In the first step, sulfuric acid thermally decomposes into SO3 and H2O. In the second step, SO3 further catalytically decomposes into SO2 and O2 . This SO3 decomposition step (also known as the oxygen-evolving step) is energy-intensive and requires a highly active and stable catalyst to decompose SO3 into SO2 and O2. In order to develop a highly active and thermally stable catalyst, several efforts have been made in the past using precious metal groups, transition metal oxides, and complex metal oxides (perovskites and spinels) . Among all, supported transition metal oxides and complex metal oxides are found to be potential alternatives to precious metal oxides due to their low cost and better stability . Although platinum-based catalysts are better catalysts, metal loss is one of the major concerns . In this regard, transition metal oxide-based catalysts supported over SiO2, Al2O3, and other support materials have been extensively explored in the literature and shown to be potential candidates for sulfuric acid decomposition . However, these transition metal oxides exhibit poor thermal stability. Therefore, complex metal oxides such as perovskites and spinels seem to be a better alternative to platinum-based catalysts due to their high thermal stability, particularly at high temperatures. Spinels are generally described by AB2O4, where A and B denote the tetrahedral and octahedral cation sites in cubic close packing of oxygens with cubic symmetry and space group Fd3𝑚 #### . The structure of spinel oxides plays a vital role in the physical and chemical properties of these spinels by accommodating different cations . These cations can occupy multiple oxidation states in different ways among A and B geometric sites. Determining inversion degree and cation distribution is necessary because these are responsible for the materials' physical and chemical properties. For normal spinels, only divalent and trivalent cations are occupied, and the inversion degree is defined as the fraction of A tetrahedral sites occupied by trivalent cations, and it is equal to zero. On the other hand, the inversion degree is equal to 1 for completely inverted spinels. Also, the preferences of cations for tetrahedral and octahedral sites, along with factors such as temperature, cooling rate, and the method of preparation, strongly influence the arrangement of cations in spinel structures.