Double‐Walled Tubular Heusler‐Type Platinum–Ruthenium Phosphide as All‐pH Hydrogen Evolution Reaction Catalyst Outperforming Platinum and Ruthenium

Abstract Nanostructured ionic compounds have driven major technological advancements in displays, photovoltaics, and catalysis. Current research focuses on refining the chemical composition of such compounds. In this study, a strategy for creating stoichiometrically well‐defined nanoscale multiple‐cation systems, where the atomically precise structure maximizes the synergistic cooperation between cations at the atomic scale is reported. The unprecedented construction of Heusler‐type PtRuP 2 double‐walled nanotubes through sequential anion/cation exchange reactions is demonstrated. The PtRuP 2 catalyst exhibits record‐high catalytic performance and durability for the hydrogen evolution reaction (HER) in alkaline electrolytes and anion‐exchange membrane water electrolyzers. The investigations highlight the crucial role of Pt/Ru dual centers, providing multiple active sites that accelerate the HER kinetics within a single phosphide material, in the sequential operation of H 2 O activation/dissociation at Ru and H 2 production at adjacent Pt sites. These findings open new avenues for optimizing ionic compound‐based HER electrocatalysts, offering platinum‐metal alternatives in acidic and alkaline media.