# Direct Solar Thermal Water-Splitting Using Iron and Iron Oxides at High Temperatures: A Review
## 7 Conclusions  
Direct solar thermal water-splitting using Fe (catalyst metal) at high temperatures is a promising development in the field of renewable energy and hydrogen production. By harnessing solar power and affordable materials, it offers a sustainable and scalable solution to the challenges of clean hydrogen production. As this technology matures and addresses its current challenges, it could come to play a vital role in transitioning to a more sustainable and greener energy future, reducing our reliance on fossil fuels and lowering carbon emissions across various industries.  
A review of the scientific literature suggests that iron will precipitate in the forms of ferrous oxide, hematite, and magnetite during the oxidation of iron in steam at high temperatures, generating hydrogen. It is therefore reasonable to assume that iron, iron oxide, and other metal oxides present in slags, such as copper slag, will also precipitate rust and hydrogen. The theoretical thermodynamic and electrochemical aspects of the reaction of metal oxides with water vapour are fundamental to the design of the solar reactor, as well as to the adequate selection of the catalyst metal.  
Future recommendations will focus on determining whether mineral waste (copper slag) containing metal oxides (iron oxides) is feasible to use as a thermocatalytic material for hydrogen production. For this purpose, a morphological and thermochemical characterization of the copper slag produced in Chile will be conducted to determine its potential use in water-splitting using a thermochemical solar reactor.  
Future research holds significant promise for advancing this technology and addressing various challenges. Here are some key areas of research that can help further develop this innovative approach: (i) materials science and corrosion resistance, (ii) efficiency enhancement, (iii) thermochemical-cycle optimization, (iv) integrated energy storage, (v) economic viability, (vi) long-term durability and reliability, (vii) scalability and modular design, (viii) hydrogen purity and quality, and (ix) market integration and policy support. Incentives to encourage the adoption of solar thermal water/steam-splitting could make this technology more efficient, cost-effective, and environmentally friendly. By addressing these research areas, we can potentially overcome the current challenges and pave the way for its widespread adoption as a clean and sustainable method for hydrogen production.  
Conceptualization, M.F. and F.M.G.M.; methodology, M.F. and F.M.G.M.; validation, A.S. ([PERSON]), E.F., D.P., A.S. ([PERSON]) and N.T.; investigation, M.F., N.T., D.P. and F.M.G.M.; writing--original draft preparation, M.F. and F.M.G.M.; writing--review and editing, M.F., A.S. ([PERSON]), E.F., D.P., A.S. ([PERSON]), N.T. and F.M.G.M.; visualization M.F., A.S. ([PERSON]) and F.M.G.M.; supervision, F.M.G.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding. The authors would like to thank the Programa de Doctorado en Energia Solar of the Universidad de Antofagasta, Chile. The authors are grateful for the support of ANID-Chile through the research projects FONDECYT Iniciacion 11230550 and ANID/ FONDAP 1522A0006 Solar Energy Research Center SERC-Chile. The authors declare no conflicts of interest.