Rigid anchoring of highly crystallized and uniformly dispersed Pd nanocrystals on carbon fibers for ambient electrocatalytic reduction of nitrogen to ammonia

Developing efficient and stable electrocatalysts for ammonia synthesis via the nitrogen reduction reaction (NRR) is essential for the Earth's nitrogen cycle. Herein, a palladium nanocrystals anchored carbon fibers (PdNCs@CNFs) composite was prepared via electrospinning and carbonization processes. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization studies show that the as-prepared Pd grains are homogeneously anchored on the outer/inner section of the carbon nanofibers. Benefiting from the sufficient exposure and stress effect of active sites, the resultant PdNCs@CNFs achieves a high Faraday efficiency of ∼14.8% with a current density of 0.028 mA cm-2 at -0.2 V vs. reversible hydrogen electrode (RHE) in 0.1 M Na2SO4 solution, surpassing those of many catalysts previously reported. Density functional theory (DFT) calculations reveal that the rationality of the distal associative mechanism on PdNCs@CNFs and Pd nanocrystals on the surface of PdNCs@CNFs is more favorable for nitrogen (N2) molecule adsorption and polarization.

Asymmetric Au-core Pd-shell nanoparticles supported on reduced graphene oxide for enhanced electrocatalytic activity

Asymmetric Au-core Pd-shell nanoparticles supported on rGO simply prepared by a GRR-like technique exhibit superior ORR performance compared to commercial Pt/C.

Microbial synthesis of Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 nanocomposites for catalytic reduction of nitroaromatic compounds

Magnetically recoverable noble metal nanoparticles are promising catalysts for chemical reactions. However, the chemical synthesis of these nanocatalysts generally causes environmental concern due to usage of toxic chemicals under extreme conditions. Here, Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 nanocomposites are biosynthesized under ambient and physiological conditions by Shewanella oneidensis MR-1. Microbial cells firstly transform akaganeite into magnetite, which then serves as support for the further synthesis of Pd, Au and PdAu nanoparticles from respective precursor salts. Surface-bound cellular components and exopolysaccharides not only function as shape-directing agent to convert some Fe3O4 nanoparticles to nanorods, but also participate in the formation of PdAu alloy nanoparticles on magnetite. All these three kinds of magnetic nanocomposites can catalyze the reduction of 4-nitrophenol and some other nitroaromatic compounds by NaBH4. PdAu/Fe3O4 demonstrates higher catalytic activity than Pd/Fe3O4 and Au/Fe3O4. Moreover, the magnetic nanocomposites can be easily recovered through magnetic decantation after catalysis reaction. PdAu/Fe3O4 can be reused in at least eight successive cycles of 4-nitrophenol reduction. The biosynthesis approach presented here does not require harmful agents or rigorous conditions and thus provides facile and environmentally benign choice for the preparation of magnetic noble metal nanocatalysts.

Synthesis of open-mouthed, yolk-shell Au@AgPd nanoparticles with access to interior surfaces for enhanced electrocatalysis

Open-mouthed, yolk–shell Au@AgPd nanoparticles are successfully produced via galvanic replacement reaction in water at room temperature.

We have successfully produced open-mouthed, yolk–shell (OM-YS) Au@AgPd nanoparticles (NPs) via galvanic replacement reaction at room temperature; each NP has a large opening on its AgPd shells. Owing to the openings on the AgPd shells, the inner surfaces of the AgPd shells of as-prepared OM-YS Au@AgPd NPs become accessible to the surrounding media. These new structural characters make the present OM-YS Au@AgPd NPs excellent catalysts for electrochemical oxidation of ethanol in alkaline media. Their electrochemical active surface area is 87.8 m² g^–1 and the mass activity is 1.25 A mg_Pd^–1. Moreover, the openings on the AgPd shells also make the surfaces of the Au cores in OM-YS Au@AgPd NPs accessible to the reaction media, which significantly facilitates the removal of CO and other carbonaceous intermediate species, thus leading to substantially enhanced durability and stability. This superior electrocatalytic performance cannot be implemented by using conventional YS Au@AgPd NPs or commercially available Pd/C catalysts.

Synchronized synthesis of Pd@C-RGO carbocatalyst for improved anode and cathode performance for direct ethylene glycol fuel cell

The simultaneous formation of a carbocatalyst composed of 5 nm sized flower-shaped Pd nanoparticles assembled on carbon–reduced graphene oxide (Pd@C-RGO) is reported via the solid state process between 1 and 2 minutes followed by microwave irradiation and exhibits improved electrocatalytic performance for the oxidation of ethylene glycol.