Enhancing Oxygen Reduction Reaction in PdHx@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.