Likai Wang

Porous Carbon-Supported Gold Nanoparticles for Oxygen Reduction Reaction: Effects of Nanoparticle Size

Porous carbon-supported gold nanoparticles of varied sizes were prepared using thiolate-capped molecular Au25, Au38, and Au144 nanoclusters as precursors. The organic capping ligands were removed by pyrolysis at controlled temperatures, resulting in good dispersion of gold nanoparticles within the porous carbons, although the nanoparticle sizes were somewhat larger than those of the respective nanocluster precursors. The resulting nanocomposites displayed apparent activity in the electroreduction of oxygen in alkaline solutions, which increased with decreasing nanoparticle dimensions. Among the series of samples tested, the nanocomposite prepared with Au25 nanoclusters displayed the best activity, as manifested by the positive onset potential at +0.95 V vs RHE, remarkable sustainable stability, and high numbers of electron transfer at (3.60-3.92) at potentials from +0.50 to +0.80 V. The performance is comparable to that of commercial 20 wt % Pt/C. The results demonstrated the unique feasibility of porous carbon-supported gold nanoparticles as high-efficiency ORR catalysts.

Ordered mesoporous carbons-supported gold nanoparticles as highly efficient electrocatalysts for oxygen reduction reaction

Unlike bulk gold, gold nanoparticles (AuNPs) have been found to exhibit apparent electrocatalytic activity for oxygen reduction reaction (ORR). In this work, glutathione-capped AuNPs of ca. 4 nm in diameter were prepared by a wet chemical method and embedded into a mesoporous carbon matrix synthesized by using an SBA-15 amorphous silica template. Pyrolysis at elevated temperatures led to removal of the organic capping ligands and the formation of ordered mesoporous carbons loaded with a selected amount of AuNPs which exhibited no apparent agglomeration. The obtained nanocomposites exhibited apparent ORR activity in alkaline media, and the sample with 20 wt% AuNPs stood out as the best among the series, within the context of onset potential, kinetic current density and stability, in comparison with AuNPs alone, ordered mesoporous carbons, and commercial Pt/C catalysts. The remarkable performance was ascribed to the intimate interactions between the AuNPs and mesoporous carbons that facilitated fast electron transfer and rapid mass transport. This is the first time that ordered mesoporous carbons were employed to support AuNPs as ORR catalysts. The strategy may be exploited to prepare a wide range of electrocatalysts based on mesoporous carbons-supported metal nanoparticles with extraordinary reactivity and enhanced stability for ORR.

In situ preparation of multi-wall carbon nanotubes/Au composites for oxygen electroreduction

Multi-wall carbon nanotubes (CNTs)/Au nanocomposites have been prepared by the in situ reduction approach. The as-prepared hybrid materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The composition of the nanocomposites was fine tuned by varying the mass ratio of Au-to-CNTs. Among a series of samples tested, hybrid materials with a Au/carbon nanotubes (Au/CNTs) ratio = 1 : 2 demonstrated the best activity towards oxygen reduction reaction (ORR), as most positive onset potential, largest kinetic current density, highest amount of electron transfer and lowest H2O2 yields were obtained. Notably, the Au/CNTs also exhibited remarkable long-term durability higher than commercial Pt/C.