Ultrafine Ru‐M Alloy@S Vacancy‐Rich MoS2 Nanosheets With Bimetallic Active Sites for Efficient Hydrogen Evolution in Alkaline and Acidic Media

A USMR synthesizes ultrafine RuCo alloy on S‐vacancy‐rich 1T phase MoS2. This method enables rapid precursor mixing, instantaneous reduction, and uniform alloy dispersion while creating S vacancies. The synergy between Ru‐Co sites and defective MoS2 optimizes hydrogen kinetics, achieving a low overpotential of 31 mV@10 mA·cm‐2 in acid, providing a scalable route for high‐performance dual‐site electrocatalysts. Abstract Developing efficient, scalable electrocatalysts for the hydrogen evolution reaction (HER) is crucial for industrial H2 production. Herein, ultrafine (≈1.7 nm) ruthenium‐cobalt (RuCo) alloys anchored on Sulfur‐vacancy‐rich 1T phase molybdenum disulfide (1T phase MoS2‐x) nanosheets (denoted as Ru2Co1‐4@E‐MoS2‐x) are synthesized via ultrasonic microreactor (USMR) technology. The USMR strategy concurrently achieves a reduced alloy size, accelerated Ru reduction kinetics, and improved metal dispersion, endowing the resulting catalysts with high metal loading and abundant accessible active sites. Experimental and theoretical analyses reveal that Co incorporation optimizes RuCo electronic structure and strengthens interfacial coupling with 1T phase MoS2‐x, lowering the Gibbs free energy of H* adsorption (ΔGH*) on both Ru and Co sites. This synergistic interaction establishes bimetallic active centers that overcome the adsorption–desorption trade‐off in single‐metal systems. In situ Raman spectroscopy further confirms that Co promotes water dissociation and hydrogen desorption at Ru sites under alkaline conditions. Consequently, Ru2Co1‐4@E‐MoS2‐x exhibits exceptional HER activity, achieving record‐low overpotentials of 31 mV in acidic and 36 mV in alkaline media at 10 mA·cm−2, significantly outperforming 20 wt% Pt/C (45 and 53 mV, respectively). Moreover, the USMR approach is universal, generating highly active RuM@E‐MoS2‐x catalysts (M = Fe, Ni, Cu). This work establishes a novel “bimetallic active sites/engineered carrier” paradigm for advanced electrocatalytic water splitting. A USMR synthesizes ultrafine RuCo alloy on S-vacancy-rich 1T phase MoS2. This method enables rapid precursor mixing, instantaneous reduction, and uniform alloy dispersion while creating S vacancies. The synergy between Ru-Co sites and defective MoS2 optimizes hydrogen kinetics, achieving a low overpotential of 31 mV@10 mA·cm-2 in acid, providing a scalable route for high-performance dual-site electrocatalysts. Abstract Developing efficient, scalable electrocatalysts for the hydrogen evolution reaction (HER) is crucial for industrial H 2 production. Herein, ultrafine (≈1.7 nm) ruthenium-cobalt (RuCo) alloys anchored on Sulfur-vacancy-rich 1T phase molybdenum disulfide (1T phase MoS 2-x ) nanosheets (denoted as Ru 2 Co 1 -4@E-MoS 2-x ) are synthesized via ultrasonic microreactor (USMR) technology. The USMR strategy concurrently achieves a reduced alloy size, accelerated Ru reduction kinetics, and improved metal dispersion, endowing the resulting catalysts with high metal loading and abundant accessible active sites. Experimental and theoretical analyses reveal that Co incorporation optimizes RuCo electronic structure and strengthens interfacial coupling with 1T phase MoS 2-x, lowering the Gibbs free energy of H * adsorption (ΔG H* ) on both Ru and Co sites. This synergistic interaction establishes bimetallic active centers that overcome the adsorption–desorption trade-off in single-metal systems. In situ Raman spectroscopy further confirms that Co promotes water dissociation and hydrogen desorption at Ru sites under alkaline conditions. Consequently, Ru 2 Co 1 -4@E-MoS 2-x exhibits exceptional HER activity, achieving record-low overpotentials of 31 mV in acidic and 36 mV in alkaline media at 10 mA·cm −2, significantly outperforming 20 wt% Pt/C (45 and 53 mV, respectively). Moreover, the USMR approach is universal, generating highly active RuM@E-MoS 2-x catalysts (M = Fe, Ni, Cu). This work establishes a novel “bimetallic active sites/engineered carrier” paradigm for advanced electrocatalytic water splitting. Advanced Science, EarlyView.