Design Principles of Platinum-Group Metallenes for Small-Molecule Electrocatalytic Conversion: from Cathodic and Anodic Half-Reactions to Coupled Electrocatalysis

Renewable electricity-driven small-molecule electrocatalytic conversion plays a pivotal role in sustainable energy utilization and value-added chemical production. The performance of these processes is governed by the adsorption and transformation of key reaction intermediates, rendering catalytic performance closely dependent on electronic structure regulation. Atomically thin platinum-group metallenes (PGM-enes), characterized by maximized surface-atom utilization and tunable electronic properties, provide an ideal platform for modulating intermediate binding and reaction pathway. Despite the rapid progress of research in this area, a systematic understanding of the intrinsic relationships among the structural characteristics of PGM-enes, intermediate adsorption behavior, and reaction pathways remains limited. In particular, a unified framework for categorizing diverse synthetic methods and structural modulation strategies from a mechanistic perspective has not yet been clearly established. To address this need, this review first examines the formation mechanisms of PGM-enes and classifies representative synthetic approaches into three fundamental based on stabilization strategies: structural inheritance, spatial confinement, and surface regulation. Building upon this foundation, structural modulation strategies are further organized into three representative pathways based on catalyst-intermediate interactions. Small-molecule electrocatalytic processes in cathodic, anodic, and coupled electrolysis are subsequently examined from a mechanistic perspective, with emphasis on the structure-electronic response characteristics of different PGM-enes and the applicability of distinct modulation strategies across reaction environments. Finally, by integrating current progress with remaining challenges, this review establishes a coherent framework for understanding structure-reactivity relationships in PGM-enes, thereby informing the rational design of future small-molecule electrocatalytic reactions.