Developing cost-effective precious metal electrocatalysts for the hydrogen evolution reaction (HER) is key to realizing the economic viability of acidic water electrolysis. Herein, galvanic displacement is employed for in situ formation of bimetallic Pt/Ru deposits on H-intercalated TiO₂ nanotube arrays. It is found that a two-step procedure yields polydisperse deposits with a dominant fraction of Ru nanoparticles coated with atomic and subnanometric Pt islands. These Pt|Ru nanointerfaces induce charge transfer from Pt to Ru, which modulates the electronic structure of Pt sites for accelerated HER kinetics. By varying the platinization time in the second step, a balance between the exposure of catalytically active Pt|Ru nanointerfaces and the total number of Pt surface sites is achieved. The optimized composite, termed Ru-30min@Pt-30min, requires an overpotential of 58 mV to deliver a current density of 100 mA cm⁻² in 1.0 m HClO₄ and maintains performance stability and structure integrity under prolonged operation. Moreover, it presents a 3.5-fold increase in precious metal mass activity over Pt/C at η = 80 mV. Theoretical calculations reveal that the electronic interactions generated by Pt-modification of Ru and hydrogenated TiO₂ surfaces provide multiple active sites with improved H_ads energetics compared to pure Pt and Ru.