Rare-Earth-Engineered High-Entropy Materials for Electrocatalytic Water Splitting

The development of highly efficient and durable electrocatalysts for water electrolysis is fundamentally constrained by sluggish reaction kinetics, limited active-site regulation, and structural degradation under harsh operating conditions. High-entropy materials (HEMs), featuring maximized compositional diversity and configurational entropy, have emerged as versatile platforms for catalytic optimization. However, the rational incorporation of rare-earth (RE) elements into high-entropy systems and their intrinsic roles in regulating catalytic behavior remain largely unexplored. Owing to their unique electronic configurations, large atomic size mismatch, variable oxidation states, and strong affinity toward oxygen species, RE elements provides additional opportunities to manipulate electronic structures, lattice distortion, defect chemistry, and surface reconstruction behaviors within high-entropy frameworks. Rather than cataloguing individual catalyst systems, this review critically organizes RE-regulated HEMs along a structure-activity chain linking the high-entropy host and RE incorporation to local coordination/electronic effects, catalytic pathways, operando reconstruction, and long-term stability. The fundamental design principles and various modulation strategies, along with their catalytic applications toward the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall/seawater electrolysis are discussed, along with emphasis on the structure-activity relationships revealed by advanced characterization techniques and theoretical calculations. Finally, the remaining challenges and perspectives associated with RE incorporation regarding the activity-stability trade-off, long-term structural evolution, resource efficiency, and practical scalability are analyzed, aiming to offer guidelines for the rational design of RE-engineered high-entropy electrocatalysts with optimized activity, stability, and practical applicability for sustainable energy conversion technologies.