Tensile-Strain-Promoted <i>In Situ</i> Electrochemical Hydrogen Intercalation Stabilizes Pd Icosahedra toward Oxygen Reduction

Understanding the strain effect in catalysis is vital for catalyst design but is complicated by the lack of model catalyst systems and strain-induced <i>in situ</i> reconstruction of the catalytically active phase. Here, we employ well-defined Pd-based model catalysts to thoroughly investigate how the surface strain impacts the oxygen reduction reaction (ORR). In contrast to the conventional expectation, Pd icosahedra (Pd-i) with a ∼2% tensile strain exhibit markedly enhanced catalytic stability toward the ORR compared to Pd octahedra (Pd-o). After 10 000 cycles of accelerated durability testing, Pd-i loses only 8.7% of its initial mass activity, while Pd-o suffers a 54.1% decline. Quasi-<i>in situ</i> spectroscopic characterizations and electrochemical analyses demonstrate that tensile strain in Pd-i promotes <i>in situ</i> hydrogen intercalation, leading to the formation of the PdH_<i>x</i> active phase. <i>In situ</i> X-ray absorption spectroscopy and theory calculations reveal that H intercalation enhances the oxidation resistance of Pd and suppresses Pd dissolution by a strong Pd-H interaction.