Fully Tensile Strained Pd₃Pb/Pd Tetragonal Nanosheets Enhance Oxygen Reduction Catalysis.

Abstract

While surface strain engineering in shaped and bimetallic nanostructures offers additional variables for manoeuvring the catalysis, manipulating isotropic strain distributions in nanostructures remains a great challenge to reach higher tiers of the catalyst's design. Herein, we report an efficient approach to construct a unique class of core/shell palladium-lead (Pd-Pb)/Pd nanosheets (NSs) and nanocubes (NCs) with homogeneous tensile strain along [001] on both the top-Pd and edge-Pd surfaces for boosting oxygen reduction reaction (ORR). These core/shell Pd-Pb/Pd NSs and Pd-Pb/Pd NCs exhibit over 160% and 140% increases in mass activity and over 114% and 98% increases in specific activity when compared with these unshelled counterparts, respectively. Especially, the Pd₃Pb/Pd NSs show the ORR mass and specific activities of 0.57 A/mg_Pd and 1.31 mA/cm² at 0.90 V versus reversible hydrogen electrode, which are 8.8 (6.5) and 9.4 (9.8) times higher than those of the commercial Pd/C (Pt/C), respectively. The valence band photoemission spectra and first-principles calculations collectively show that the tensile strained Pd shell results in an upshift of the d-band-center of Pd, weakening the chemisorption of oxygenated species due to the contribution of the antibonding orbital. In addition, the Pd₃Pb/Pd NSs and NCs with intermetallic core and homogeneous few layers of Pd shell can sustain at least 20 000 potential cycles with negligible activity decay and composition changes. The present work provides a new direction for the design of highly active and stable catalysts for fuel cells and beyond.