# Direct Solar Thermal Water-Splitting Using Iron and Iron Oxides at High Temperatures: A Review
## 6 Discussion
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**Reactor Geometry** & **Bed/Gas** & **Material** & **Power/Radiation** & **Reactor** & **Year/Refs.** \\ \hline Tube with 40 mm & & Pure iron metal tube, & & & \\ inner diameter, 10 & Quartz sand/air & & hot particle container & \\ mm wall thickness, & & made of stainless & & \\ and 1780 mm length & & steel AISI 304 & & & \\ \hline \hline \end{tabular}
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Table 7: _Cont._issues of material degradation. Economic-viability research involves cost-reduction strategies, life-cycle analysis, and scalability studies. These efforts aim to make the technology economically feasible by reducing manufacturing costs, understanding the full economic and environmental impacts, and exploring possibilities for large-scale production. One of the main advantages of this method is the use of a thermochemical iron (Fe) catalyst, which is not only cost-effective but also widely available, primarily in copper slag--an industrial waste. This waste contains a variety of metal oxides that can be utilized. Despite the lack of evidence for copper slag's use as a catalyst material for hydrogen production through thermolysis, it was found that copper slag in Chile contains a significant concentration of fayalite, comprising two moles of iron oxide (FeO) and one mole of silicon oxide (SiO\({}_{2}\)). This utilization not only reduces the overall cost of the process but also enhances its sustainability and feasibility for large-scale implementation. It's noteworthy that the United States Geological Survey (USGS) estimates there are vast iron-ore reserves, further emphasizing the accessibility of this material. For instance, in 2017, gross iron ore reserves were estimated at an impressive 170,000 million metric tons, with an iron content of approximately 82,000 million metric tons. However, the 2016 production was only 2106 million metric tons, highlighting the vast untapped potential. Moreover, the technology's capability to efficiently split water into hydrogen (H\({}_{2}\)) and oxygen (O\({}_{2}\)) at high temperatures is crucial. It offers an effective solution for storing excess solar energy as hydrogen, which can be utilized in fuel cells or other applications during periods of reduced or no sunlight. This effectively tackles one of the key issues with solar power--intermittency--and contributes to a more reliable and consistent energy supply. Nonetheless, it is critical to recognize that the high operating temperatures place considerable stress on the materials, especially the electrodes and electrolyzers. This necessitates the development of advanced engineering solutions to ensure the technology's longevity, durability, and cost-effectiveness over the long term. Additionally, optimizing the system design and energy conversion efficiency remains a significant challenge that must be overcome to enhance the competitiveness of this process relative to other hydrogen-production methods. While this technology has immense potential, its practicality and impact are inherently linked to the solar resources and local conditions of the region in which it is deployed. Geographical areas with abundant sunlight stand to benefit the most, making this innovation particularly well-suited for regions with high solar potential. As we continue to refine and develop this technology, it has the potential to play a crucial role in transitioning towards a more sustainable and environmentally friendly energy landscape.