Unconventional‐Phase Pd 20 Te 7 Octahedra With High‐Index Facets for Oxygen Reduction

ABSTRACT The high surface energy leads to a significant challenge in the chemical synthesis of high‐index faceted nanomaterials. While the preparation of unconventional‐phase palladium (Pd)‐based nanocrystals with high‐index facets is largely unexplored. Herein, we introduce ethylene glycol as the morphology and size controller for unconventional‐phase Pd 20 Te 7 nano‐octahedra (NOs) enclosed by {300}, {20}, and {23} high‐index facets. These facets endow Pd 20 Te 7 NOs with excellent electrocatalytic activity for alkaline oxygen reduction reaction. Their high mass activity of 1.91 A mg Pd −1 at 0.90 V (vs. RHE) demonstrates a 1.89‐fold enhancement relative to Pd 20 Te 7 nanoparticles (NPs). More importantly, the Pd 20 Te 7 NOs‐based membrane electrode assembly (MEA) achieves a peak power density of 0.59 W cm −2 and a mass activity of 14.33 A mg PGM −1 (PGM: platinum group metals), measured in H 2 ‐O 2 fuel cells at an internal resistance‐corrected voltage of 0.65 V, corresponding to a 1.22‐fold and 2.47‐fold enhancement compared to Pd 20 Te 7 NPs (0.49 W cm −2 and 5.81 A mg PGM −1 ). Furthermore, the Pd 20 Te 7 NOs‐based MEA demonstrates stable operation at 0.4 A cm −2 for nearly 1440 min under an ultralow Pd loading of 0.022 mg cm −2 on the cathode. This work offers a new avenue to rationally design and construct high‐index faceted nanocrystals for high‐efficiency catalytic applications.