# Direct Solar Thermal Water-Splitting Using Iron and Iron Oxides at High Temperatures: A Review
## 6 Discussion  
The latest technological devices that have been designed and manufactured for the recovery of solar hydrogen using photovoltaic technology, such as solar concentration, direct water-splitting using solar thermal energy with Fe electrodes, and FenOm-type oxides operating at high temperatures are an example of the multiple types of sustainable alternatives to address the global energy crisis. This method directly harnesses solar energy, enhancing sustainability and scalability. By improving efficiency, solar thermal water-splitting presents a viable pathway for large-scale hydrogen production, contributing to the broader adoption of sustainable hydrogen technologies. Furthermore, using Fe or Fe\({}_{\text{n}}\)O\({}_{\text{m}}\) electrodes at high temperatures offers a complementary approach by potentially reducing overpotential through high-temperature operation; additionally, these materials are abundant and low-cost, whether they are obtained through direct extraction or recycling. The experimental setup for direct solar thermal water-splitting using Fe electrodes involves the use of concentrated solar energy to achieve and maintain the high temperatures necessary for the reaction. A solar concentrator focuses sunlight onto a reactor chamber, heating it to temperatures between 800 \({}^{\circ}\)C and 1000 \({}^{\circ}\)C. Within this high-temperature environment, the iron electrodes act as thermochemical catalysts, facilitating the water-splitting reaction by cycling between oxidation and reduction states. The abundance and low cost of iron make it an attractive choice for this process. High temperatures improve the catalytic activity and stability of iron, addressing some common challenges associated with non-precious-metal catalysts. This setup exemplifies a sustainable and efficient method for hydrogen production, leveraging solar energy and abundant materials to contribute to the development of renewable-energy technologies. Non-precious transition metals such as cobalt and nickel are attractive for electro-catalysis due to their low cost. However, challenges related to conductivity, catalytic activity, maintenance of active surface sites, and geopolitical issues (with regard to cobalt) hamper their widespread application. Advances in materials science have focused on the improvement of iron-based alloys or compounds and on surface modifications with high corrosion resistance. These improvements can increase the catalytic properties, active-site density, and durability of the electrodes, overcoming problems of material degradation. High-temperature operation improves the conductivity and catalytic activity of Fe and Fe\({}_{\text{n}}\)O\({}_{\text{m}}\), generating a higher density of active surface sites. The oxidation of iron in steam at high temperatures produces a significant amount of H\({}_{2}\), demonstrating the high efficiency and reactivity of Fe under these thermal conditions. The high-temperature environment accelerates the reaction rate and improves the purity of the produced H\({}_{2}\), making the process suitable for various applications. These results support the viability of using Fe and Fe\({}_{\text{n}}\)O\({}_{\text{m}}\) catalysts in solar thermochemical cycles. To advance the technology of direct solar thermal water-splitting using Fe electrodes at high temperatures, several specific areas of future research have been recommended. Improvements in materials science focus on developing Fe-based alloys or composites, surface modifications, and corrosion-resistance techniques. These advancements can improve catalytic properties and increase active-site density and electrode durability, overcoming