Dynamic surface activation of PtNiRu medium-entropy alloy catalysts for durable PEM water electrolysis

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Durable, low-loading platinum-group metal (PGM) catalysts for the hydrogen evolution reaction (HER) are critical for advancing proton exchange membrane water electrolysis (PEMWE). Here, we report a continuous-flow synthesis of ultrasmall (1.5 ± 0.5 nm) PtNiRu medium-entropy alloy nanoparticles on defect-rich few-layer graphene (FLG) to form (Pt 5 Ni 3 Ru 2 @G). This approach overcomes the asynchronous reduction kinetics of conventional batch methods, yielding a homogeneous single-phase solid solution with surface Ni O species, a pre-catalyst architecture revealed by synchrotron X-ray absorption spectroscopy. During acidic HER, electrochemical surface activation of the pre-catalyst progressively lowers the overpotential from 123 to 70 mV at 0.1 A cm −2 , while the Tafel slope decreases from 60.36 to 35.74 mV dec −1 . Post- operando characterizations show surface Ni O species are reduced under cathodic polarization, while Pt and Ru electronic structures remain unchanged. Translation to a single-cell PEMWE device confirms the activation mechanism and the Pt 5 Ni 3 Ru 2 @G-based cell delivers 1.0 A cm −2 at 1.6 V, while exhibiting operational stability for over 300 h at 0.5 A cm −2 . Notably, such remarkable durability is achieved with 20.5% PGM-loading, potentially reducing PEMWE cost. The findings establish continuous-flow synthesis as a versatile protocol for producing entropy-stabilized alloy catalysts with dynamically restructuring surfaces for durable, PGM-reduced water electrolysis.