Review of Rare Earth Metal Nanocomposite Catalysts for Electrochemical Water Splitting

Electrochemical water splitting presents a promising method for producing hydrogen, a cleaner and more sustainable fuel. However, its broader application is hindered by the limited availability and high cost of noble metal electrocatalysts, such as platinum, iridium, palladium, and ruthenium, which are known for their efficiency in facilitating water splitting. Rare earth metals, with their distinctive 4f electronic configurations, versatile valencies, robust metal–oxygen interactions, and tunable electronic properties, demonstrate significant potential in reducing energy barriers for water-splitting reactions. They effectively optimize the d band center and enhance the adsorption/desorption energies of intermediates involved in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) while also offering corrosion resistance and improved intrinsic performance. This review delves into the structure–function relationships that influence HER and OER performance in rare earth metal-based systems, focusing on three mechanistic pathways such as the adsorbed evolution mechanism (AEM), lattice oxygen mechanism (LOM), and oxide path mechanism (OPM) for HER and OER. The integration of rare earth metals with transition metals further enhances charge transfer and conductivity through f–d orbital interactions. Various design strategies, including vacancy formation, morphology manipulation, heteroatom doping, interface engineering, and surface reconstruction, are employed to optimize the catalytic performance at elevated current densities. Nonetheless, challenges related to extraction methods and environmental impacts remain. By linking structural characteristics to catalytic performance, this review aims to provide insights for a rational catalyst design and highlight critical knowledge gaps that need to be addressed to propel rare-earth-based electrocatalysis toward scalable and sustainable energy generation in the form of catalytic hydrogen production.