Forward-Reverse Bismuth Doping Enables an Anisotropic Transition From Stable to Metastable Ruthenium for Alkaline Hydrogen Evolution

Metastable electrocatalyst phases, with tailored electronic structures, unsaturated coordination sites, and tuned d-band centers, offer exciting opportunities for enhanced catalysis. This work demonstrates p-block bismuth doping to stabilize an electrocatalytically active metastable body-centered tetragonal phase in ruthenium nanosheets via a symbiotic forward-reverse doping mechanism. Bi initially occupies the body center of hexagonal close-packed Ru to stabilize the secondary body-centered tetragonal phase, while excess Bi induces another metastable body-centered cubic Bi phase through reverse Ru doping into the Bi lattice. The resulting anisotropic elongation of Ru lattice and the metastable body-centered tetragonal phase optimize the binding of hydrogen evolution reaction intermediates in alkaline media. The 10 at % Bi-doped system, comprising 98.5% hexagonal Ru0.92Bi0.08 and 1.5% body-centered tetragonal Ru0.475Bi0.525, delivers ultralow overpotentials of 31 ± 7 and 126 ± 13 mV at 10 and 100 mA cm−2, respectively, with stable operation for over 20 days. This catalyst achieves a 3.4-fold enhancement in specific activity and turnover frequency over Ru while also rivaling 20 wt % Pt/C. In situ Raman spectroscopy reveals suppressed hydroxide poisoning, restructured interfacial water, and accelerated *OH-mediated steps. Theoretical calculations show that Bi-induced charge redistribution and band-center modulation in both phases optimize water adsorption, thereby promoting hydrogen production.