Abstract: Achieving efficient electrocatalysis for the Hydrogen Evolution Reaction (HER) and Hydrogen Oxidation Reaction (HOR) is of great significance for establishing a hydrogen economy and promoting sustainable social development. Ruthenium (Ru), with its inherent high oxophilicity, is regarded as a highly promising electrocatalyst for alkaline hydrogen electrocatalysis. In this work, transition metal cadmium (Cd) was introduced to regulate the surface electronic structure of Ru, optimize the binding energies of adsorbed active hydrogen (H*) and hydroxyl (OH*) on Ru, and effectively promote electron transfer. A carbon-nanotube-supported Ru–Cd composite (Ru–Cd/CNT) with low Ru loading was successfully fabricated. Electrochemical measurements demonstrate that the as-prepared catalyst exhibits highly efficient and stable catalytic performance toward both HOR and HER. In 0.1 mol/L KOH electrolyte for HOR, the Ru–Cd/CNT catalyst achieves a geometric kinetic current density (j_k) of 16.31 mA·cm⁻² at an overpotential of 50 mV (vs. RHE), which is 5 and 9 times higher than those of commercial Pt/C and Ru/C catalysts, respectively. Its geometric exchange current density (j₀) reaches 2.05 mA·cm⁻², also superior to commercial Pt/C and Ru/C. For HER, Ru–Cd/CNT delivers an overpotential of only 34 mV at a current density of 10 mA·cm⁻², much lower than commercial Pt/C (65 mV) and Ru/C (60 mV). Furthermore, Ru–Cd/CNT shows excellent CO tolerance and stability in alkaline HOR/HER measurements: the current density decreases by only 8% after 2000 s operation in the presence of 0.1% CO, and by merely 10% after 12000 s continuous operation, both outperforming commercial Pt/C and Ru/C. This study provides a new strategy and important reference for developing high-performance and sustainable electrode materials for hydrogen–oxygen fuel cells.