A partial ligand exchange strategy for fabricating catalytically active single palladium site immobilized on zeolitic imidazolate framework-8 (ZIF-8, Pd₁/ZIF-8) is proposed in this work. The one-step synthesis simply involves reacting Na₂PdCl₄ with ZIF-8 in solvent. The Cl ligands of Na₂PdCl₄ exchanged with 2-methylimidazole (2-MeIm) of the framework, resulting in the anchoring Pd on the framework and dissociation of Zn into the solution. The whole synthesis is performed at ambient conditions and the crystalline integrity of ZIF-8 is well retained. The resulting Pd₁/ZIF-8 is extensively characterized by different techniques which confirm the proposed mechanism. Pd₁/ZIF-8 is also successfully applied in the size-selective semi-hydrogenation of alkynes.

NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction (OER). However, their practical applications still suffer from poor conductivity, limited activity, and durability. To address these issues, herein, by utilizing three-dimensional covalent organic framework (3D-COF) with porous confined structures and abundant coordinate N sites as the precursor, the partially oxidized Ni₃Fe nanoalloys wrapped by N-doped carbon (N-C) layers are constructed via simple pyrolysis and subsequent oxidization. Benefiting from the 3D curved hierarchical structure, high-conductivity of Ni₃Fe and N-C layers, and well-distributed active sites, the as-synthesized O-Ni₃Fe-N-C catalyst demonstrates excellent activity and durability for catalyzing OER. Experimental and theoretical analyses disclose that both high-temperature oxidization and the OER process greatly promote the formation and exposure of the Ni(Fe)OOH active species as well as lower charge transfer resistance, inducing its optimized OER activity. The robust graphitized N-C layers with superior conductivity and their couplings with oxidized Ni₃Fe nanoalloys are beneficial for stabilizing catalytic centers, thereby imparting O-Ni₃Fe-N-C with such outstanding stability. This work not only provides a rational guidance for enriching and stabilizing high-activity catalytic sites towards OER but also offers more insights into the structural evolution of NiFe-based OER catalysts.