Chiajen Hsu

Synthesis of highly active and stable Au–PtCu core–shell nanoparticles for oxygen reduction reaction

Au-PtCu core-shell nanoparticles were successfully synthesized via galvanic replacement of Cu by Pt on hollow Au nano-spheres. Characterizations of the nanoparticles were conducted by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical measurements. Results indicate 2-2.5 times higher specific activity and mass activity of the Au-PtCu catalysts than commercial Pt black and Pt/C in oxygen reduction reaction (ORR), measured in a rotating disk electrode system. Besides, thinner PtCu coating (25 nm thick, deposition time of 20 min) on the hollow Au nano-spheres demonstrated a pronounced CO oxidation peak shift (by 0.13 V) and long-term durability probably due to the unique core-shell structure and strong electronic coupling between the Au core and the PtCu shell.

Au/Pd core-shell nanoparticles with varied hollow Au cores for enhanced formic acid oxidation.

A facile method has been developed to synthesize Au/Pd core-shell nanoparticles via galvanic replacement of Cu by Pd on hollow Au nanospheres. The unique nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, and electrochemical measurements. When the concentration of the Au solution was decreased, grain size of the polycrystalline hollow Au nanospheres was reduced, and the structures became highly porous. After the Pd shell formed on these Au nanospheres, the morphology and structure of the Au/Pd nanoparticles varied and hence significantly affected the catalytic properties. The Au/Pd nanoparticles synthesized with reduced Au concentrations showed higher formic acid oxidation activity (0.93 mA cm-2 at 0.3 V) than the commercial Pd black (0.85 mA cm-2 at 0.3 V), suggesting a promising candidate as fuel cell catalysts. In addition, the Au/Pd nanoparticles displayed lower CO-stripping potential, improved stability, and higher durability compared to the Pd black due to their unique core-shell structures tuned by Au core morphologies.

Improving the catalytic activity of Au/Pd core–shell nanoparticles with a tailored Pd structure for formic acid oxidation reaction

Unique morphology-tunable Au/Pd core–shell nanoparticles were synthesized by galvanic replacement of preformed Cu on hollow Au cores using different PdCl2 concentrations. The nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical analysis. The results showed that the structure of the nanocrystalline Pd on the hollow Au core surface was strongly dependent on the PdCl2 concentration. It was found that Pd2+ ions transport and react in the porous Cu layer, helping to create a continuous but porous structure which enlarges the Pd surface area and increases the electrochemical activity. In addition, the Au/Pd core–shell nanoparticles displayed superior electrochemical performance and stability in formic acid oxidation than commercial Pd black, especially for the ones synthesized using 2.5 mM PdCl2. The enhanced electrocatalytic performance may be attributed to the optimum electronic coupling effect caused by the interaction between the specific Pd structure and the hollow Au core.