Facet-dependent degradation of Pd nanocubes and surface stabilization via atomic-level Pt modification

Single-crystal Pd nanocubes with preferential (100) facets were synthesized as model catalysts to probe the intrinsic activity and stability limits of Pd-based electrocatalysts for methanol oxidation. The nanocubes deliver a mass activity of 1140 mA mg^-1 at 0.9 V, nearly twice that of Pt/C. Despite this impressive activity, accelerated durability tests reveal pronounced performance decay, arising from facet-dependent structural degradation rather than catalyst detachment. Identical-location TEM combined with in-situ Raman spectroscopy uncovers that adsorbed hydroxyl intermediates trigger Pd dissolution, lattice reconstruction, and interparticle coalescence, leading to severe loss of electrochemically active surface area. Guided by these mechanistic insights, we introduced an atomic-level surface modification by depositing an ultrathin Pt overlayer on Pd nanocubes. The resulting Pd@Pt nanocubes preserve the cubic architecture, achieve an enhanced mass activity of 1506 mA mg^-1, and exhibit substantially improved stability with >50% retention after extended operation. The suppression of hydroxyl-induced poisoning and coalescence highlights the role of interfacial electronic tuning in stabilizing active surfaces. This work elucidates the facet-specific degradation pathways of Pd catalysts and establishes surface modification as a generalizable strategy toward designing durable, high-performance electrocatalysts for alcohol oxidation.