Temperature-dependent lithium migration and increased thermal stability within palladium nanoparticles

Abstract

The incorporation of light-element dopants into monometallic nanoparticle catalysts enables precise modulation of their electronic structures, thereby tailoring catalytic performance. However, despite the widespread use and general understanding of such systems, fundamental aspects of dopant–framework interactions and solid-solution behavior in light-element-doped metal nanoparticles remain incompletely characterized. Here, using a one-step synthesis of lithiated palladium (Pd) nanoparticles formed by an in situ lithiation process with lithium (Li) acetate, we investigate the temperature-dependent phase behavior of the Pd–Li solid solution by variable-temperature synchrotron powder X-ray diffraction (VT-SPXRD). In situ thermal Bragg diffraction studies reveal unexpected delithiation dynamics and phase complexity in the metastable PdLi intermetallic compound, including previously unreported temperature-dependent lithium migration and site-occupancy redistribution. Remarkably, we demonstrate that interstitial lithium doping enhances thermal stability from 150 °C to over 400 °C, with higher lithium loadings (0.5–1.5 eq) maintaining structural integrity up to 515 °C. This unexpected stabilization, attributed to nanoparticle encapsulation effects, provides fundamental insight into light-element doping mechanisms in metallic nanoparticles and paves the way for the rational design of electronically tuned nanocatalysts.