Bridging Bulk and Surface Thermodynamics: A Hybrid Pourbaix Framework for Electrocatalyst Stability

Abstract A long-term durability of electrocatalysts remains a central challenge, particularly for nonprecious metal catalysts that often exhibit high activity but suffer from rapid degradation under practical operating conditions. A major degradation pathway is the dissolution of active metal sites as ionic or oxidized species at the surface–electrolyte interface, which remains difficult to capture using conventional computational approaches. Here, we introduce the hybrid Pourbaix diagram as a unified framework that integrates bulk and surface thermodynamics to assess the stability of surface metal atoms against dissolution, the redox behavior of adsorbates under electrochemical conditions, and the ion (de)intercalation from and into the crystal lattice. By combining density functional theory (DFT) calculations of such surface phenomena with experimentally reported bulk thermodynamic data, the hybrid Pourbaix diagram describes pH- and potential-dependent stability across surface-bound and dissolved states. The framework is flexible to incorporate grand-canonical (GC) DFT to account for potential-dependent electronic effects and applicable to different types of systems and reactions. We demonstrate the versatility of this approach through representative case studies including Ti–N–C for nitrate reduction, Fe–N–C for oxygen reduction with potential-induced spin-state transitions, and α-K0.125MnO2 surfaces involving Mn dissolution and K+ deinsertion. The hybrid Pourbaix diagram provides a practical platform for analyzing catalyst stability and activation, guiding the design of durable and active electrocatalysts.