Unraveling the Bimetallic Synergy: A Unified Framework for Synthesis, Dynamic Evolution, and Multi-Electron Electrocatalysis.

Bimetallic electrocatalysts provide additional geometric and electronic degrees of freedom for regulating multi-electron reactions and can relax the scaling constraints encountered at monometallic sites in favorable cases. However, rational development of such catalysts remains challenging due to the mismatch between static as-synthesized structures and dynamically evolving active sites under operating conditions. This Review presents an integrated framework connecting synthesis, structural evolution, characterization, and multi-electron electrocatalytic behaviors. Representative bimetallic systems, ranging from alloys, intermetallics, heterointerfaces, and core-shell structures to atomically dispersed dual-metal sites are compared in terms of structural precision, scalability, and ability to control metal-metal proximity. Key characterization approaches are summarized, highlighting the necessity of combined microscopy, spectroscopy, operando analysis, isotope labeling, and theoretical calculations to validate genuine bimetallic synergy. Applications are discussed across water splitting (HER/OER), oxygen reduction (ORR), CO2 reduction (CO2RR), nitrogen-cycle conversion (NOxRR), and electrochemical urea synthesis (EUS). Across these systems, two universal synergy modes are identified: electronic/geometric tuning to optimize intermediate adsorption and functional site division to enable tandem multi-step reactions. Finally, challenges in controllable dynamic reconstruction, structural durability under industrial conditions, together with prospects of data-driven catalyst discovery are outlined to guide scalable catalyst development.