From ceria water-splitting cycles to rare-earth-doped electrodes and photocatalysts, researchers are examining which material properties matter most for cleaner hydrogen production.
Paper: Circular utilization of rare earth elements in green hydrogen technologies. AI-generated abstract conceptual image created using ChatGPT/OpenAI
A recent review in the journal Scientific Reviews explores how rare earth elements (REEs) could support cleaner or more efficient hydrogen production across thermochemical, electrochemical, photocatalytic, membrane-based, and biomass-conversion technologies. The review focuses on ceria-based water-splitting materials, rare-earth-modified reforming catalysts, electrolysis electrodes, photoelectrochemical systems, hydrogen-storage materials, biomass-gasification catalysts, and REE recycling strategies.
Addressing the Hydrogen Production Challenge
Hydrogen is an important energy carrier for fuel cells, transportation, energy storage, and industrial applications. Most hydrogen is still produced through fossil-fuel-based processes. While these technologies are mature and economically competitive, they depend on non-renewable feedstocks and generate substantial greenhouse-gas emissions. Their energy-intensive operation, environmental impacts of fossil-fuel extraction, and additional needs for purification, compression, storage, and transport strengthen the case for cleaner production pathways.
Rare earth elements (REEs) offer a materials-based strategy to improve hydrogen-generation technologies. The 17 REEs possess distinctive magnetic, optical, electrical, and catalytic properties. Several REE-containing materials provide oxygen storage capacity, oxygen mobility, and reversible redox behavior. REEs can modify electronic structure, surface acidity and basicity, defect concentration, metal dispersion, and resistance to catalyst deactivation.
The review surveys a broad range of REE-containing materials used in steam reforming, electrolysis, photoelectrochemical hydrogen generation, thermochemical water splitting, membrane technologies, hydrogen storage, and biomass gasification.
Evaluating Rare Earth-Based Materials and Catalytic Strategies
The review covers a broad range of rare earth-containing mixed oxides, perovskites, composites, and supported catalysts. Researchers have investigated perovskite-type materials such as LaNiO3, LaNi1-xFexO3, and LaNi1-xCoxO3 for methane reforming. Iron-based composites with cerium and zirconium have also shown strong activity for ammonia cracking. These studies use various material characterization techniques to relate crystal structure, surface chemistry, morphology, and reaction performance.
The authors discuss synthesis strategies including impregnation, co-precipitation, sol-gel processing, and hydrothermal synthesis, explaining how each method influences catalyst composition, surface properties, and hydrogen-production performance. Hybrid preparation methods combine these advantages and may improve activity, selectivity, and long-term stability.
The review highlights the distinct roles of individual REEs. Cerium supports oxygen storage, oxygen release, and redox catalysis, while lanthanum acts as a catalyst promoter and dopant and is also used in hydrogen-storage materials. Other REEs contribute to hydrogen purification and storage, photocatalysis, electrochemical reactions, and membrane technologies. These findings show why REE selection should reflect the reaction mechanism and operating conditions.
Applications of hydrogen using rare earths.
Materials and Mechanisms Shape Hydrogen Production
The reviewed studies demonstrate that REEs serve as simple catalyst additives and also actively modify the physicochemical properties that control catalytic reactions. In ceria-based materials, oxygen mobility and vacancy formation play particularly important roles in regulating redox behavior. During thermochemical water splitting, CeO2 cycles reversibly between reduced and oxidized states, supporting repeated hydrogen-generation cycles.
Researchers can further tune these properties by introducing dopants such as samarium, which can improve oxygen-ion conductivity and redox characteristics. Controlled REE doping can therefore be used to tailor the high-temperature performance of hydrogen-generation materials. Ceria can reduce carbon deposition through its oxygen mobility, while Co- Pr2O3 interactions and the formation of lanthanum dioxycarbonate can also suppress carbon accumulation.
Rare-earth incorporation can enhance electrochemical performance by facilitating both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Doping modifies electronic structure, increases active-site availability, and lowers reaction overpotentials. Examples include Dy-doped CuO, La-doped Co3O4, and Ni-Ce systems. In solid-oxide electrolysis, lanthanum strontium cobalt ferrite combines favorable oxygen-ion conductivity with high-temperature stability.
Photocatalytic and photoelectrochemical systems benefit from complementary mechanisms. Rare earth incorporation can extend light absorption, introduce beneficial defect states, improve charge-carrier separation, and suppress electron-hole recombination. La-modified Co3O4, La-modified MoS2, and Nd2O3/g-C3N4 composites show how heterostructure and defect engineering can improve photocatalytic performance. Nd2O3/g-C3N4 achieved a hydrogen-generation rate of 4355.34 μmol g-¹ h-¹, approximately 9.5 times higher than that of pure g-C3N4.
Across these studies, several key material descriptors consistently govern hydrogen-production performance, including oxygen mobility, oxygen-vacancy concentration, surface acidity and basicity, metal-support interactions, electronic structure, charge-carrier separation, and resistance to carbon deposition. The review links these descriptors to rational catalyst design and defect engineering.
Assessing Rare Earth Materials for Sustainable Hydrogen Technologies
Rare-earth-based materials have improved hydrogen production performance in laboratory studies across several routes. REEs are expensive, geographically concentrated, and environmentally challenging to extract and process. Further research must address catalyst stability, material compatibility, long-term durability, and optimal dopant concentrations, while demonstrating that laboratory-scale performance can translate to larger systems under realistic operating conditions.
Future work should test rare-earth catalysts using renewable electricity, solar energy, and low-carbon feedstocks. REE supply and extraction impacts should be assessed alongside catalyst performance. Recycling, recovery, and reuse can reduce the environmental burden of REE extraction and processing. Researchers should assess REE cost alongside contributions to efficiency, durability, energy savings, and catalyst lifetime.
Advancing these materials from laboratory studies to practical hydrogen technologies will require clear structure-property relationships, durability testing, techno-economic assessment, and integration with renewable-energy systems.
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