Seeded Synthesis of Unconventional 2H-Phase Pd Alloy Nanomaterials for Highly Efficient Oxygen Reduction

Crystal phase engineering of noble-metal-based alloy nanomaterials paves a new way to the rational synthesis of high-performance catalysts for various applications. However, the controlled preparation of noble-metal-based alloy nanomaterials with unconventional crystal phases still remains a great challenge due to their thermodynamically unstable nature. Herein, we develop a robust and general seeded method to synthesize PdCu alloy nanomaterials with unconventional hexagonal close-packed (hcp, 2H type) phase and also tunable Cu contents. Moreover, galvanic replacement of Cu by Pt can be further conducted to prepare unconventional trimetallic 2H-PdCuPt nanomaterials. Impressively, 2H-Pd₆₇Cu₃₃ nanoparticles possess a high mass activity of 0.87 A mg^-1Pd at 0.9 V (vs reversible hydrogen electrode (RHE)) in electrochemical oxygen reduction reaction (ORR) under alkaline condition, which is 2.5 times that of the conventional face-centered cubic (fcc) Pd₆₉Cu₃₁ counterpart, revealing the important role of crystal phase on determining the ORR performance. After the incorporation of Pt, the obtained 2H-Pd₇₁Cu₂₂Pt₇ catalyst shows a significantly enhanced mass activity of 1.92 A mg^-1_Pd+Pt at 0.9 V (vs RHE), which is 19.2 and 8.7 times those of commercial Pt/C and Pd/C, placing it among the best reported Pd-based ORR electrocatalysts under alkaline conditions.