Facet‐Tailored <scp> Co ₃ O ₄ </scp> as Electronic Regulator and Stabilizing Support for Ru Nanocluster: Toward Efficient Alkaline <scp>HER</scp>

Ruthenium‐based catalysts are promising alternatives to platinum for the hydrogen evolution reaction (HER) due to their comparable activity and lower cost. However, their widespread application in alkaline water electrolysis is limited by insufficient stability and excessive hydrogen binding. Herein, the Ru@Co 3 O 4 nanosheets (Ru@Co 3 O 4 NSs) featuring dominant exposure of the Co 3 O 4 (111) facets and precise anchoring of Ru nanoclusters onto these planes were constructed. The interaction between Ru nanoclusters and the Co 3 O 4 (111) facets induces a downshift of the Ru d ‐band center, optimizes the interfacial water network, and simultaneously prevents the leaching of Ru species. Ru@Co 3 O 4 NSs deliver exceptional alkaline HER performance, with an overpotential of 9.8 mV at 10 mA cm −2 and robust durability over 1000 h at 1 A cm −2 . The catalyst also achieves a price‐normalized activity of 145.9 A $ −1 , nearly nine times that of commercial Pt/C. When applied in an anion exchange membrane water electrolyzer (AEMWE), Ru@Co 3 O 4 NSs reveal a low cell voltage of 1.93 V at 1 A cm −2 and operate stably for 60 h with a minimal degradation rate of 0.67 mV h −1 . This work provides a promising approach for designing low‐cost, high‐performance Ru‐based catalysts for sustainable hydrogen production.