Facile synthesis of palladium hierarchical nanosheet assemblies: unraveling the aggregation-induced synergistic effect for enhanced methanol oxidation reaction activity

Abstract

This study presents a facile strategy for synthesizing hierarchical palladium (Pd) nanosheet assemblies with enhanced methanol oxidation reaction (MOR) activity. The nanostructures were engineered through a one-pot co-reduction approach, where sodium tetrachloropalladate(II) was co-reduced by ascorbic acid and citric acid in an ice water bath. Mechanism studies suggested that the dendritic seeds formed at early stages directed the hierarchical assembly of Pd nanosheets, where the lamellar micelle structure of octadecyltrimethylammonium group guides the anisotropic 2D growth of Pd nanosheets. Due to the interconnected, porous nanosheet networks with high electrochemically active surface areas, electrochemical evaluations revealed an aggregation-induced synergistic effect, where the densely packed nanosheet assemblies exhibited a mass activity of 276.1 mA mg_Pd⁻¹ and a specific activity of 1.92 mA cm⁻²—values 2.1 times and 4 times higher, respectively, than those of benchmark Pt/C catalysts. Density functional theory (DFT) simulations suggest that the tensile lattice strain of Pd enhances the adsorption ability of adsorbed species during the MOR and consequently boosts catalytic activity. This work not only advances the design of high-performance MOR catalysts but also elucidates the critical role of nanoscale aggregation in amplifying electrocatalytic performance.