Coupled s-p-d Exchange in Facet-Controlled Pd₃Pb Tripods Enhances Oxygen Reduction Catalysis

Efficient oxygen reduction reaction (ORR) catalysts are key for the development of high-performance fuel cells. Palladium (Pd) is a promising catalyst system for ORR given its potential to replace platinum (Pt); however, it usually exhibits lower activity than Pt. Here, we report a class of ordered Pd₃Pb tripods (TPs) with predominantly {110} facets and show that they achieve extremely high ORR performance in alkaline medium. In contrast to the knowledge that the excellent ORR activity of Pt catalyst is caused by its partially filled d orbital, our first-principle calculations suggest that the strong charge exchange between Pd-4d and Pb-(sp) orbitals on the Pd₃Pb TPs {110} facet results in a Pd-Pb local bonding unit with an orbital configuration similar to that of Pt. Consequently, Pd₃Pb TPs exhibit much higher ORR activities than commercial Pt/C and commercial Pd/C. Pd₃Pb TPs are endurable and sustain over 20,000 potential cycles with negligible structural and compositional changes. Efficient catalysts for oxygen reduction reactions (ORRs) are the most decisive factor in high-performance fuel cells to meet energy supplies and industrial needs. Palladium (Pd) has been proposed to catalyze ORR well in alkaline media, but it usually exhibits much lower activity than platinum (Pt). Most reported Pd-based catalysts are limited to zero-dimensional (0D) nanocrystals (NCs), which are not beneficial for improving ORR stability. Moreover, ordered intermetallic NCs are attracting more attention because of their outstanding catalytic properties and high chemical and structural stabilities. Here, we report a class of ordered Pd₃Pb tripods (TPs) with predominantly {110} facets. The strong coupled s-p-d exchange effect on {110} faceted Pd₃Pb TPs plays a decisive role in boosting ORR, resulting in their greatly enhanced ORR performance over that of Pt/C. This study opens a new route in the rational design of high-efficiency Pd-based catalysts with proper facet and ordering control to enhance ORR catalysis. Guo and colleagues have successfully created a class of ordered Pd₃Pb tripods (TPs) with predominantly {110} facets and show that they can achieve an unprecedented ORR activity in alkaline solution. First-principal calculations indicated that the enhanced ORR activity in Pd₃Pb TPs can be attributed to a strong coupled s-p-d exchange effect on the {110} facets, which makes Pd₃Pb TPs exhibit much higher ORR activities than commercial Pt/C and commercial Pd/C. © 2018 Elsevier Inc.