Synthesis of Monodispersed Pd Nanoparticles and Ultrathin Twisty Pd Nanowire Networks for Electrooxidation of Ethanol.

In recent years, preparing precious metal catalysts with a controllable morphology has become a hot research topic for researchers. In this study, monodispersed palladium (Pd) nanoparticles (NP) and ultrathin Pd twisty nanowire networks (TNN) were synthesized in a solvothermal system using N,N-dimethylformamide (DMF) and oleylamine (OAm) as solvents, Transmission electron microscopy (TEM) images reveal the successful synthesis of nanoparticles and ultrathin TNN microstructures. Electrochemical data show that the current densities of Pd-NP and Pd-TNN for the ethanol oxidation reaction (EOR) reach 1878 mA mg-1 and 1765 mA mg-1, respectively. Compared to commercial Pd/C, Pd-TNN and Pd-NP exhibit better catalytic stability, lower electron transfer barriers, and more resistance to catalyst poisoning. Temperature, pH value, and ethanol concentration are all favorable for the EOR. According to the experimental data, the mechanism of enhanced electrocatalytic activity of Pd-NP and Pd-TNN catalysts for ethanol oxidation is discussed. This paper presents a method for preparing catalysts with stabilized structures to develop Pd-based catalysts for electrocatalytic oxidation reactions.

Assembly of Alloyed PdM (Ag, Cu, and Sn) Nanosheets and Their Electrocatalytic Oxidation of Ethanol and Methanol.

Direct alcohol fuel cells are popular due to their high energy density, abundant sources, and ease of transportation and storage. Palladium-based nanosheet self-assembled materials have emerged as an effective catalyst for alcohol oxidation reactions. In this work, nanosheets were synthesized with the same feeding ratio assembly of alloyed PdM (M = Ag, Cu, and Sn). The introduction of the second element was able to enhance the catalytic response of the catalysts to alcohol electrooxidation. Among them, the PdCu alloy exhibited the best performance in terms of catalytic activity, toxicity resistance, and stability to ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). The catalytic current densities for EOR can reach 2226, 2518, and 1598 mA mg-1 for PdAg, PdCu, and PdSn nanosheet assemblies, respectively. These are mainly attributed to better electronic effects, altered atomic distances within the cell for the d-band centers of Pd, and a larger electrochemical active surface area (ECSA). The optimized d-band center is beneficial to promote the catalytic performance of EOR and MOR. Experimental data also demonstrated that higher electrocatalytic temperature, higher pH, and higher alcohol concentration can accelerate the rate of alcohol electrooxidation. These results have the potential to be extended to Pd-M (M = other metals) nanosheets and help for a wider range of catalytic applications.

Pd-Enriched-Core/Pt-Enriched-Shell High-Entropy Alloy with Face-Centred Cubic Structure for C1 and C2 Alcohol Oxidation.

High-entropy alloy nanoparticles (HEA NPs) have aroused great interest globally with their unique electrochemical, catalytic, and mechanical properties, as well as diverse activity and multielement tunability for multi-step reactions. Herein, a facile low-temperature synthesis method at atmospheric pressure is employed to synthesize Pd-enriched-HEA-core and Pt-enriched-HEA-shell NPs with a single phase of face-centred cubic structure. Interestingly, the lattice of both Pd-enriched-HEA-core and Pt-enriched-HEA-shell enlarge during the formation process of HEA, with tensile strains included in the core and shell of HEA. The as-obtained PdAgSn/PtBi HEA NPs show excellent electrocatalytic activity and durability for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The specific (mass) activity of PdAgSn/PtBi HEA NPs for MOR is 4.7 mA cm-2 (2874 mA mg(Pd+Pt) -1 ), about 1.7 (5.9) and 1.5 (4.8) times higher than that of commercial Pd/C and Pt/C catalysts, respectively. Additional to high-entropy effect, Pt sites and Pd sites on the interface of the HEA act synergistically to facilitate the multi-step process towards EOR. This study offers a promising way to find a feasible route for scalable HEA manufacturing with promising applications.

Morphology Variation of Ternary PdCuSn Nanocrystalline Assemblies and Their Electrocatalytic Oxidation of Alcohols.

Metal alloys not only increase the composition and spatial distribution of elements but also provide the opportunity to adjust their physicochemical properties. Recently, multimetallic alloy nanocatalysts have attracted great attention in energy applications and the chemical industry. This work presents the production of three ternary PdCuSn nanocrystalline assemblies with similar compositions via a one-step hydrothermal method. The shape variation of assembly units from nanosheets and nanowires to nanoparticles were realized by adjusting the percentage of Sn in metal precursors. Experimental data show that PdCuSn nanowire networks showed the best catalytic activity by virtue of their optimized morphological characteristics and microscopic electronic structure. With electrooxidation of methanol, ethanol, ethylene glycol, and glycerol at 30 °C, PdCuSn nanowire networks demonstrated catalytic activity of 1129, 2111, 2540, and 1445 mA mg-1, respectively. The catalytic activity for alcohol oxidation is attributed to the production of the electronic structure and morphology features that are most suitable. This is achieved by introducing the proper quantities of Cu and Sn components in the first stage of synthesis. This study would help with the construction of high-efficiency nanostructured alloy catalysts by regulating the electronic structure and morphology.