2D Topological Electrocatalysts with Spin-Orbit Coupling: Interplay between the "Electrochemical" and "Topological" Surface States.

Two-dimensional (2D) topological materials have emerged as promising candidates for electrocatalysis owing to their exotic surface electronic structures governed by spin-orbit coupling (SOC). However, under realistic electrochemical conditions, these surface electronic properties can be significantly adjusted by the dynamic reconstruction of catalyst surfaces, referred to as electrochemical surface states (ESSs), which remains underexplored in the context of topological materials. Here, using monolayer PtBi2 as a model catalyst, we reveal that the SOC-enabled topological surface states (TSSs) of PtBi2 can be actively modulated by ESSs even without inducing structural phase transitions. Through density functional theory computations, we identify that ∼1 monolayer (ML) of HO* adsorbates dominates the surface under oxygen reduction reaction (ORR) conditions, inducing localized SOC-enabled states and a flat band with high density near the Fermi level. This reconstructed TSS landscape improves orbital coupling with oxygen intermediates and reduces the electrostatic dipole sensitivity, leading to optimal adsorption energetics for the ORR. pH-dependent microkinetic simulations further confirm that this interplay drives the system to near-peak ORR activity. Extension study to other redox-relevant ESSs (e.g., H*- and O*-covered surfaces) and different 2D topological materials, like PdBi2 and MoTe2, highlights the broader relevance of this mechanism. This study establishes a mechanistic framework linking ESSs and TSSs in 2D topological materials, emphasizing that the associated SOC effects are crucial and that they should not be dismissed in related electrocatalyst design.