Highly Stabilized and Accessible Sub‐Nanometer RuBi Heteroclusters Drive Efficient Alkaline Hydrogen Evolution

ABSTRACT Controlling the size and interfacial structure of bimetallic hetero‐clusters below two nanometers represents a key challenge in catalyst design due to their thermodynamic tendency to undergo sintering and phase segregation. This work presents a dual spatial confinement strategy to synthesize uniformly dispersed, sub‐nanometer RuBi bimetallic hetero‐clusters embedded within porous carbon nanofibers (RuBi HCs/PCNFs). The synthetic approach utilizes the internal pores of metal‐organic frameworks as primary nano‐reactors, coupled with an electrospun polymer matrix as a secondary physical barrier, preventing metal migration and coalescence during high‐temperature pyrolysis. We employ the alkaline hydrogen evolution reaction (HER) as a probe to evaluate the efficacy of this structural design. Characterizations and theoretical analysis show that the atomic proximity and electronic interactions between Ru and Bi optimize intermediate adsorption and accelerate the rate‐determining water dissociation step. Benefiting from these structural and electronic advantages, the RuBi HCs/PCNFs catalyst delivers enhanced electrocatalytic HER activity and robust operational durability. When evaluated in an anion exchange membrane (AEM) water electrolyzer, the catalyst demonstrates stable, long‐term operation, showcasing the practical utility of the hetero‐cluster configuration. This study demonstrates the feasibility of utilizing dual spatial confinement to construct stable, sub‐nanometer bimetallic platforms for electrocatalytic applications.