Engineering the Atomic Layer of RuO₂ on PdO Nanosheets Boosts Oxygen Evolution Catalysis

We report an atomic-scale controllable synthesis of the face-centered cubic Ru overlayers on Pd nanosheets (Pd@Ru NSs) by a solution-based epitaxial growth method. The thickness of Ru overlayers can be accurately tuned at an atomic level, which has been confirmed by atomic force microscopy and high-angle annular dark-field scanning transmission electron microscopy. After annealing in air, the Pd@Ru NSs were transformed to PdO@RuO2 NSs with rutile RuO2 epitaxially grown on the PdO. The oxygen evolution reaction (OER) activity and stability strongly depend on the atomic layers of RuO2 and ∼4 atomic layers of RuO2 (PdO@RuO2-4layers) exhibit superior stability and optimal activity for OER with only 257 mV of the overpotential to reach 10 mA cm–2. Density functional theory calculations well reproduce the thickness dependence of OER activity and reveal that O* binds more weakly on the PdO@RuO2-4layers that boosts the rate-determining step for formation of HOO*, assuring the best OER performance.