Mesoporous Pt@PtM (M = Co, Ni) cage-bell nanostructures toward methanol electro-oxidation

DFT Study on Methanol Oxidation Reaction Catalyzed by PtmPdn Alloys

Pt is widely used as the catalyst for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFC). However, the high cost and limited supply of pure Pt limit the commercialization of DMFC. Herein, MOR catalyzed by variously designed Pd-doped PtmPdn was studied with the density functional theory (DFT); the PtmPdn(111) surface was chosen since it is the most stable surface among various low-index surfaces. The hydrogens in methyl groups were priorly dehydrogenated on Pt(111), followed by hydrogen in the hydroxyl group. The effects of both the ratio of Pt:Pd and the type of the alloy on the activity of PtmPdn catalysts toward MOR were also studied; both ordered and disordered PtPd with the 1:1 ratio had better catalytic activity towards MOR than other catalysts. Specifically, the disordered Pt:Pdd with the Pt:Pd ratio of 1:1 had the best activity for the relatively stronger adsorption of COH, but the lowest binding with CO and a moderate d band center. The adsorptions of both COH and CO are key steps in the MOR, since the steps of CH3OH→CH2OH→CHOH→COH have downhill energy profiles, while COH→CO is an uphill reaction. In addition, the d band centers of the surface atoms move towards the Fermi level with the increase of the Pd content; the d band can also be tuned by changing the atom arrangement. These findings can be used as rules to design high-performance catalysts for MOR.

Facile Synthesis of Urchin-like Hollow Au Crystals for In Situ SERS Monitoring of Photocatalytic Reaction

Hollow urchin-like Au nanocrystals have been widely studied due to their excellent surface plasmon resonance properties and large specific surface area, but the controllable preparation of hollow urchin-like Au nanocrystals is still a challenge. In this article, we successfully prepared hollow urchin-like Au nanocrystals using HAuCl4·3H2O and AgNO3 as precursors and ascorbic acid as the reducing agent. No surface ligands or polymer stabilizers are required in the preparation process. HAuCl4·3H2O and AgNO3 will first form AgCl cubes, then the reducing agent, ascorbic acid, will reduce the Au3+ in the solution to Au0, and Au0 will be deposited on the pre-formed AgCl cubes to form AgCl@Au nanocrystals. We characterized the morphology of the prepared Au nanocrystals by scanning electron microscopy and found that by increasing the amount of HAuCl4·3H2O in the reaction, the surface morphology of the Au nanocrystals would change from a rough spherical shape to an urchin-like shape. By further increasing the amount of the precursor HAuCl4·3H2O, urchin-like Au will convert into flake-like morphology. The AgCl in the interior was removed with ammonia water, and finally, hollow urchin-like Au crystals were formed. In addition, we used R6G molecule to explore the surface-enhanced Raman spectroscopy (SERS) enhancement effect of prepared Au crystals. The results show that the minimum detectable concentration of R6G reaches 10−8 M. Moreover, we applied hollow urchin-like Au nanocrystals as catalysts and SERS enhancing materials to detect the photocatalytic reaction of 4-NTP. We used a 785 nm laser as both the SERS light source and the catalytic light source to monitor the photocatalytic effect of the laser on 4-NTP in situ by adjusting the laser power.