Polypeptide Polymer Brushes by Light-Induced Surface Polymerization of Amino Acid N-Carboxyanhydrides.

Silicon wafers are decorated with photoamine generator 4,5-dimethoxy-2-nitrobenzyl 3-(triethoxysilyl)propyl carbamate. UV-irradiation in the presence of benzyl-l-glutamate N-carboxyanhydride is carried out, resulting in the release of the surface-bound primary amines, making them viable N-carboxyanhydride (NCA) polymerization initiators. Successful polypeptide grafting is confirmed by water contact angle measurements as well as by ellipsometry, revealing a poly(benzyl-l-glutamate) (PBLG) layer of ≈3 nm. X-ray photoelectron spectroscopy confirms the presence of amide groups in the grafted PBLG while time-of-flight secondary ion mass spectroscopy provides additional evidence for the presence of PBLG on the surface. Evaluation of negative control samples confirms successful UV surface grafting. The approach is thus established as a viable general method for light exposure directable polypeptide functionalization of silicon surfaces.

Early stages of catalyst aging in the iridium mediated water oxidation reaction.

When exposed to a potential exceeding 1.5 V versus RHE for several minutes the molecular iridium bishydroxide complex bearing a pentamethylcyclopentadienyl and a N-dimethylimidazolin-2-ylidene ligand spontaneously adsorbs onto the surface of glassy carbon and gold electrodes. Simultaneously with the adsorption of the material on the electrode, the evolution of dioxygen is detected and modifications of the catalyst structure are observed. XPS and XAS studies reveal that the species present at the electrode interface is best described as a partly oxidized molecular species rather than the formation of large aggregates of iridium oxide. These findings are in line with the unique kinetic profile of the parent complex in the water oxidation reaction.

Electrolyte Effects on the Stability of Ni-Mo Cathodes for the Hydrogen Evolution Reaction.

Water electrolysis to form hydrogen as a solar fuel requires highly effective catalysts. In this work, theoretical and experimental studies are performed on the activity and stability of Ni-Mo cathodes for this reaction. Density functional theory studies show various Ni-Mo facets to be active for the hydrogen evolution reaction, Ni segregation to be thermodynamically favorable, and Mo vacancy formation to be favorable even without an applied potential. Electrolyte effects on the long-term stability of Ni-Mo cathodes are determined. Ni-Mo is compared before and after up to 100 h of continuous operation. It is shown that Ni-Mo is unstable in alkaline media, owing to Mo leaching in the form of MoO4 2- , ultimately leading to a decrease in absolute overpotential. It is found that the electrolyte, the alkali cations, and the pH all influence Mo leaching. Changing the cation in the electrolyte from Li to Na to K influences the surface segregation of Mo and pushes the reaction towards Mo dissolution. Decreasing the pH decreases the OH- concentration and in this manner inhibits Mo leaching. Of the electrolytes studied, in terms of stability, the best to use is LiOH at pH 13. Thus, a mechanism for Mo leaching is presented alongside ways to influence the stability and make the Ni-Mo material more viable for renewable energy storage in chemical bonds.

In situ structural evolution of single particle model catalysts under ambient pressure reaction conditions.

The catalytic activity of metal nanoparticles can be altered by applying strain, which changes the crystalline lattice spacing and modifies the electronic properties of the metal. Understanding the role of elastic strain during catalytic reactions is thus crucial for catalyst design. Here, we show how single highly faceted Pt nanoparticles expand or contract upon interaction with different gas atmospheres using in situ nano-focused coherent X-ray diffraction imaging. We also demonstrate inter-particle heterogeneities, as they differ in development of strain under CO oxidation reaction conditions. The reported observations offer new insights into the design of catalysts exploiting strain effects.

Supported nickel-rhenium catalysts for selective hydrogenation of methyl esters to alcohols.

The addition of Re to Ni on TiO2 yields efficient catalysts for the hydrogenation of acids and esters to alcohols under mild conditions. Rhenium promotes the formation of atomically dispersed and sub-nanometre-sized bimetallic species interacting strongly with the oxide support.