Lithium-Mediated Hydrochloric Acid Dissolution: Enabling Clean and Efficient Recovery of Palladium from Spent Catalysts by Electrodeposition.

To address palladium supply-demand challenges and conventional recovery inefficiencies, this study develops a lithium-mediated electrodeposition process for efficient palladium recycling from spent catalysts. Density functional theory calculations identified a controlled Pd→LiPd (Pd)→LiPdO (Pd) transformation pathway, and experimental verification confirmed that LiPd precursors underwent oxidative transformation into LiPdO with structural inheritance. LiPdO exhibited Pd-O coordination and underwent rapid dissolution in dilute hydrochloric acid. Pd exhibits a quasi-reversible redox process, thereby eliminating multivalent-state-induced efficiency losses. Field simulations demonstrated that the anisotropic current distribution in the 2D electrode plane drove the edge effects, which directly controlled the annular palladium deposition at the base. Electrodeposition produced a phase-pure palladium deposit with high (111)-textured crystallinity and ultralow lattice strain. Elevated voltages enhanced the nucleation density, inducing a morphological transition from dendritic to compact clusters, while the amplified edge effects promoted the formation of mossy structures. Elevated Pd concentrations triggered mass-transfer-driven competitive growth, resulting in the transition of palladium deposits from uniform grains to particles with graded size distributions. This work addresses the critical challenge of inefficient palladium dissolution using a phase-engineering strategy and establishes an integrated dissolution-electrodeposition framework that enables the high-efficiency recovery of secondary palladium resources.