Confined Ru–B–Ni Atomic Bridges for Exceptional Acidic Hydrogen Evolution

Ru-based electrocatalysts for acidic hydrogen evolution still suffer from a trade-off between activity and durability. Here we report a Ni-catalyzed in-situ top-growth strategy to confine ternary Ru–B–Ni active moieties inside self-supported carbon nanotubes. B serves as an atomic bridge that covalently couples Ru and Ni, inducing strong intermetallic electronic modulation. This shifts the d-band center and optimizes the Gibbs free energy of hydrogen adsorption to near-neutral −0.05 eV. The tubular carbon scaffold provides spatial confinement, effectively suppressing agglomeration and acidic dissolution of the embedded Ru–B–Ni sites. As a result, the optimal Ru–B–Ni/CNTs catalyst requires only 34 mV overpotential at 10 mA cm^–2 with a Tafel slope of 12.6 mV dec^–1 in 0.5 M H₂SO₄. Its mass activity reaches 100 A mg^–1 at –0.23 V, and the turnover frequency is 53 s^–1, outperforming commercial Pt/C. The catalyst sustains stable operation for 200 h at 100 mA cm^–2, and when assembled in a practical PEM electrolyzer, runs continuously for 525 h at 1 A cm^–2 with negligible voltage decay. This synergy of atomic bridging and nanotube confinement provides a robust and scalable pathway toward high-performance, durable Ru-based cathodes for water electrolysis.