Enhancing Oxygen Reduction Reaction in PdH _x @Pt Metallenes: Unveiling the Impact of Ligand Beyond Strain Effect

Abstract Incorporating interstitial non‐metal atoms within the crystal lattice of catalysts enables flexible modulation of their electronic structures and catalytic performances. However, the resulting induced tensile strain typically has a detrimental effect on oxygen reduction reaction (ORR) activity. In this study, a series of PdH x @Pt metallenes with varying H/Pd ratios, where hydrogen atoms precisely modulate the strain and ligand effects on the Pt skin surface is reported. Notably, PdH 0.35 @Pt metallenes exhibit an extraordinary half‐wave potential of 0.933 V and a mass activity (MA) of 7.36 A mg Pt −1 at 0.9 V vs reversible hydrogen electrode (RHE) for ORR, outperforming both Pd@Pt metallenes and commercial Pt/C catalysts. Control experiments and density functional theory (DFT) calculations reveal a competitive relationship between strain and ligand effects across different H/Pd ratios, with a dominant positive ligand effect overcoming the negative strain effect at an H/Pd ratio of 0.35. This electronic structure modulation leads to an increased 5d electron density of the surface Pt and a downshift in the e g * band center, thereby weakening the adsorption of oxygen intermediates on the Pt skin surface and resulting in excellent ORR activity.