Using Elemental Se and Ag to grow pure Ag2Se dendrites/dendritic-films of highly oriented (001) nanocrystals

A clean, facile route of using only common bulk selenium (Se) powder and silver (Ag) foil in a simple solvothermal process is developed to synthesize a film of silver selenide (Ag2Se) dendrites of highly oriented (001) nanocrystals. The simple process takes ∼10 h at 160 °C in a common alcohol such as methanol or ethanol in an autoclave, and the reaction time is shorter than in many prevalent methods. The adoption of elemental Se and Ag (foil) in the synthesis eases the control of the purity of the product, simplifies the reaction steps, and reduces the costs, as the synthesis does not require Se and Ag compounds, and also requires no chemical additives other than an alcohol as solvent. The results support a mechanism of dissolution of the bulk-like Se powder in the solvothermal process, transport of solvated Se to react with Ag, nucleation of Ag2Se nanocrystals, surface-mediated, solvation-assisted surface diffusion of Ag2Se nanocrystals, and diffusion-limited aggregation of the Ag2Se nanocrystals through oriented attachment for the growth of dendrites having highly oriented (001) nanocrystals. The clean, relative facile route is practical for the fabrication of Ag2Se crystals/films with hierarchically ordered nanostructures for future applications in solar cell devices. More importantly, the same concept can be adopted for the synthesis of other nanomaterials with bulk elemental reactants with no reliance on chemical compounds or additives

PtPd Hybrid Composite Catalysts as Cathodes for Proton Exchange Membrane Fuel Cells

In this work, PtPd hybrid cathodic catalysts were prepared for a proton exchange membrane fuel cell (PEMFC) application by two different strategies. The first strategy was the physical mixing of bimetallic PtPd onto partially reduced graphene oxide (PtPd/rGO) and PtPd onto multi-walled carbon nanotubes (PtPd/MWCNT); (PtPd/rGO) + (PtPd/MWCNT). The second strategy was physical mixing of both carbonaceous supports before the PtPd deposition to form PtPd/(rGO:MWCNT). Our experimental results revealed that the PtPd nanomaterial prepared over a mixture of both carbonaceous supports had better oxygen reduction reaction (ORR) and PEMFC performances than the individually prepared catalysts. The insertion of MWCNT between rGO sheets prevented their stacking. This promoted the diffusion of oxygen molecules through the interlayer spacing, enhancing the ORR’s electrocatalytic activity. The durability test demonstrated that the hybrid supporting material dramatically improved the catalyst’s stability even after 3000 reaction cycles. This highlighted an increase greater than 100% for hybrid nanocomposites in their electrocatalytic activity as compared with the PtPd/rGO nanocomposite

Ultra-Low Pt Loading in PtCo Catalysts for the Hydrogen Oxidation Reaction: What Role Do Co Nanoparticles Play?

The effect of the nature of the catalyst on the performance and mechanism of the hydrogen oxidation reaction (HOR) is discussed for the first time in this work. HOR is an anodic reaction that takes place in anionic exchange membrane fuel cells (AEMFCs) and hydrogen pumps (HPs). Among the investigated catalysts, Pt exhibited the best performance in the HOR. However, the cost and the availability limit the usage. Co is incorporated as a co-catalyst due to its oxophylic nature. Five different PtCo catalysts with different Pt loading values were synthesized in order to decrease Pt loading. The catalytic activities and the reaction mechanism were studied via electrochemical techniques, and it was found that both features are a function of Pt loading; low-Pt-loading catalysts (Pt loading < 2.7%) led to a high half-wave potential in the hydrogen oxidation reaction, which is related to higher activation energy and an intermediate Tafel slope value, related to a mixed HOR mechanism. However, catalysts with moderate Pt loading (Pt loading > 3.1%) exhibited lower E1/2 than the other catalysts and exhibited a mechanism similar to that of commercial Pt catalysts. Our results demonstrate that Co plays an active role in the HOR, facilitating Hads desorption, which is the rate-determining step (RDS) in the mechanism of the HOR