High Entropy Materials in Electrocatalysis: A Critical Review of Structure–Property Understanding

High entropy materials (HEMs) have emerged as a promising new class of electrocatalysts distinguished by their immense compositional flexibility and structural complexity, which can give rise to unprecedented catalytic properties and open new avenues for fundamental insight into catalysis. Realizing the potential of HEM electrocatalysts is dependent on building a deep understanding of structure-property relationships, based on nuanced characterization of both structural and electrochemical properties. This critical review navigates the current landscape of HEMs in electrocatalysis, exploring the evolving nomenclature and conceptual frameworks that shape how these materials are described and understood across the literature. We consider the diverse characterization techniques used to investigate the structure of HEMs, discussing the length scales and chemical contrasts they provide as well as the challenges associated with characterizing highly complex, multielement systems. Building on this foundation, we highlight key studies of HEMs in electrocatalysis, including those focused on screening the vast compositional space of HEMs to identify new electrocatalysts, or else examining the activity and stability of HEM electrocatalysts in detail, drawing insights into the factors that govern their performance. This critical review also emphasizes emerging research directions and strategies where advanced characterization and design approaches may help unlock the full potential of HEMs in electrocatalytic applications.