OH regulator of highly dispersed Ru sites on host Pd nanocrystals for selective ethanol electro-oxidation

The ethanol oxidation reaction (EOR) is crucial in direct alcohol fuel cells and chemical production. However, the electro-oxidation of ethanol molecules to produce acetaldehyde and carbon monoxide can poison the active sites of nanocatalysts, resulting in reduced performance and posing challenges in achieving high activity and selectivity for ethanol oxidation. In this study, we employed a dynamic seed-mediated method to precisely modify highly dispersed Ru sites onto well-defined Pd nanocrystals. The oxyphilic Ru sites serve as "OH valves", regulating water dissociation, while the surrounding Pd atomic arrangements control electronic states for the oxidation dehydrogenation of carbonaceous intermediates. Specifically, Ru_0.040@Pd nanocubes (Ru:Pd = 0.04 at.%), featuring (100) facets in Ru-Pd₄ configurations, demonstrate an outstanding mass activity of 6.53 A·mg_Pd⁻¹ in EOR under alkaline conditions, which is 6.05 times higher than that of the commercial Pd/C catalyst (1.08 A·mg_Pd⁻¹). Through in-situ experiments and theoretical investigations, we elucidate that the hydrophilic Ru atoms significantly promote the dynamic evolution of H₂O dissociation into OH_ads species, while the electron redistribution from Ru to adjacent Pd concurrently adjusts the selective oxidation of C₂ intermediates. This host–guest interaction accelerates the subsequent oxidation of carbonaceous intermediates (CH₃CO_ads) to acetate, while preventing the formation of toxic *CH_x and *CO species, which constitutes the rate-determining step.