Pd Nanoparticles with Twin Structures on F‐Doped Graphene for Formic Acid Oxidation

Gas-pressure-assisted strategy for precise control of palladium-based nanoparticle sizes: Unveiling size effects on methanol oxidation activity

Understanding the relationship between catalyst particle size and activity is crucial for developing efficient catalytic systems. However, the size-dependent behavior of Pd-based alloy catalysts remains poorly understood, requiring a comprehensive investigation. This study presents a straightforward and effective gas-pressure-assisted heat-treatment method that allows precise control over the particle sizes of various Pd-based catalysts, including Pd, Pd3Fe, Pd3Co, Pd3Ni, and Pd3Cu. Our findings demonstrate that high pressure significantly inhibits nanoparticle sintering by increasing energy barriers for both metal atomic diffusion and nanocluster migration. A linear relationship has been established between average particle size and applied gas pressure. Specifically, this method was employed to synthesize Pd3Fe nanoparticles (NPs) with an average particle size ranging from 2.8 to 6.9 nm. Furthermore, we explored the size effect of Pd3Fe/C in the methanol oxidation reaction (MOR). The mass activity (MA) of the catalyst exhibited a volcano-shaped trend as particle size decreased. Notably, the Pd3Fe/C-7 MPa catalyst with a particle size of 3.9 nm demonstrated superior MA compared to other samples within this range of sizes tested in this study. This work offers a valuable approach for systematically studying the size effect on catalytic performance, which aids researchers in designing high-performance catalytic materials.

Freestanding Penta-Twinned Pd-Ag Nanosheets

2D metal nanosheets have attracted significant attention as efficient catalysts for various important chemical reactions. However, the development of metal nanosheets with controlled compositions and morphologies has been slow due to the challenges associated with synthesizing thermodynamically unfavorable 2D structures. Herein, we report a synthesis route of freestanding Pd-Ag penta-twinned nanosheets (Pd-Ag ptNSs) with distinct 5-fold twin boundaries. Through the coreduction of Ag and Pd precursors on presynthesized Pd ptNSs, Ag could be homogeneously alloyed with Pd, leading to the formation of well-defined Pd-Ag ptNSs. The promotional effects of the bimetallic composition, 2D structure, and twin boundaries on catalysis were studied by using Pd-Ag ptNS-catalyzed H2 production from formic acid decomposition as a model reaction. Notably, the catalytic activity of the Pd-Ag ptNSs drastically outperformed those of monometallic, bimetallic, and 3D counterparts, such as Pd ptNSs, Pd-Ag nanosheets without a TB, and Pd-Ag octahedral nanocrystals, demonstrating the promising potential of the integration of twin boundaries and multiple compositions in the development of high-performance 2D nanocatalysts.

Engineering the morphology of palladium nanostructures to tune their electrocatalytic activity in formic acid oxidation reactions

Pd nanomaterials can be cheaper alternative catalysts for the electrocatalytic formic acid oxidation reaction (FAOR) in fuel cells. The size and shape of the nanoparticles and crystal engineering can play a crucial role in enhancing the catalytic activities of Pd nanostructures. A systematic study on the effect of varying the morphology of Pd nanostructures on their catalytic activities for FAOR is reported here. Palladium nanoparticles (Pd_0D), nanowires (Pd_1D) and nanosheets (Pd_2D) could be synthesized by using swollen liquid crystals as 'soft' templates. Swollen liquid crystals are lyotropic liquid crystals that are formed from a quaternary mixture of a surfactant, cosurfactant, brine and Pd salt dissolved in oil. Pd_1D nanostructures exhibited 2.7 and 19 fold higher current density than Pd_0D and Pd_2D nanostructures in the FAOR. The Pd_1D nanostructure possess higher electrochemically active surface area (ECSA), better catalytic activity, stability, and lower impedance to charge transfer when compared to the Pd_0D and Pd_2D nanostructures. The presence of relatively higher amounts of crystal defects and enriched (100) crystal facets in the Pd_1D nanostructure were found to be the reasons for their enhanced catalytic activities.