Direct Solar Thermal Water-Splitting Using Iron and Iron Oxides at High Temperatures: A Review

Green hydrogen is poised to play a crucial role in the energy-transition process in developed countries over the coming years, particularly in those countries aiming to achieve net-zero emissions. Consequently, the for green hydrogen is expected to rise significantly. This article explores the fundamental methods of producing hydrogen, focusing on the oxidation reaction within a thermochemical solar cycle for the dissociation of steam. Solar thermochemical cycles have been extensively researched, yet they remain in the development stage as research groups strive to identify optimal materials and conditions to enhance process efficiency, especially at high temperatures. The article analyses theoretical foundations drawn from exhaustive scientific studies related to the oxidation of iron in steam, the relationship with the activation energy of the corrosive process, thermodynamic aspects, and the kinetic model of a heterogeneous reaction. Additionally, it presents various mechanisms of high-temperature oxidation, pH effects, reactors, and materials (including fluidized beds). This scientific review suggests that hydrogen production via a thermochemical cycle is more efficient than production via electrochemical processes (such as electrolysis), provided the limitations of the cycle’s reduction stage can be overcome.