Thermochemical Water-Splitting (TCWS) is a promising approach for generating clean hydrogen (H₂) by employing the waste heat originating from different sources. High-temperature requirements and temperature swing approach hinder the widespread adoption of TCWS for clean hydrogen production. This study explores ceria nanorods (CeNRs) as a potential solution for overcoming these limitations. Herein, we report, the TCWS in a fixed bed reactor using CeNRs at low and constant temperature of 400 °C. We systematically explore the influence of synthesis parameters on the resulting CeNRs, including the selection of ceria precursor, effect of calcination, and their impact in TCWS. It was found that CeNRs prepared using cerium chloride as the precursor exhibited enhanced TCWS activity, resulting significantly higher total H₂ yield 4.74 mL/g, at a constant temperature of 400 °C in three redox cycles. Moreover, X-ray Photoelectron Spectroscopy (XPS) analysis confirms the presence of both Ce³⁺ and Ce⁴⁺ states within the structure, with Ce³⁺ constituting approximately 30 % and Ce⁴⁺ accounting for approximately 70 % of the total cerium content. Additionally, Raman spectroscopy corroborates the presence of a higher concentration of oxygen vacancy which are beneficial for increasing the hydrogen production. We demonstrate that ceria in its nanorod structure having exposed higher proportions of (110) and (100) planes and higher concentration of oxygen vacancies is beneficial for lowering TCWS temperature as well as increasing the hydrogen yield.

The interest in and need for carbon-free fuels that do not rely on fossil fuels are constantly growing from both environmental and energetic perspectives. Green hydrogen production is at the core of the transition away from conventional fuels. Along with popularly investigated pathways for hydrogen production, thermochemical water splitting using redox materials is an interesting option for utilizing thermal energy, as this approach makes use of temperature looping over the material to produce hydrogen from water. Herein, two-step thermochemical water splitting processes are discussed and the key aspects are analyzed using the most relevant information present in the literature. Redox materials and their compositions, which have been proven to be efficient for this reaction, are reported. Attention is focused on non-volatile redox oxides, as the quenching step required for volatile redox materials is unnecessary. Reactors that could be used to conduct the reduction and oxidation reaction are discussed. The most promising materials are compared to each other using a multi-criteria analysis, providing a direction for future research. As evident, ferrite supported on yttrium-stabilized zirconia, ceria doped with zirconia or samarium and ferrite doped with nickel as the core and an yttrium (III) oxide shell are promising choices. Isothermal cycling and lowering of the reduction temperature are outlined as future directions towards increasing hydrogen yields and improving the cyclability.