Adsorption and oxidation of carbon monoxide on a rhodium electrode studied by in-situ infrared spectroscopy

Enabling Overall Water Splitting on Photocatalysts by CO-Covered Noble Metal Co-catalysts

Photocatalytic overall water splitting requires co-catalysts that efficiently promote the generation of H₂ but do not catalyze its reverse oxidation. We demonstrate that CO chemisorbed on metal co-catalysts (Rh, Pt, Pd) suppresses the back reaction while maintaining the rate of H₂ evolution. On Rh/GaN:ZnO, the highest H₂ production rates were obtained with 4-40 mbar of CO, the back reaction remaining suppressed below 7 mbar of O₂. The O₂ and H₂ evolution rates compete with CO oxidation and the back reaction. The rates of all reactions increased with increasing photon absorption. However, due to different dependencies on the rate of charge carrier generation, the selectivities for O₂ and H₂ formation increased in comparison to CO oxidation and the back reaction with increasing photon flux and/or quantum efficiency. Under optimum conditions, the impact of CO to prevent the back reaction is identical to that of a Cr₂O₃ layer covering the active metal particle.

Surface-enhanced infrared absorption spectroscopy (SEIRAS) to probe monolayers of membrane proteins

Surface-enhanced infrared absorption spectroscopy (SEIRAS) represents a variation of conventional infrared spectroscopy and exploits the signal enhancement exerted by the plasmon resonance of nano-structured metal thin films. The surface enhancement decays in about 10nm with the distance from the surface and is, thus, perfectly suited to selectively probe monolayers of biomembranes. Peculiar to membrane proteins is their vectorial functionality, the probing of which requires proper orientation within the membrane. To this end, the metal surface used in SEIRAS is chemically modified to generate an oriented membrane protein film. Monolayers of uniformly oriented membrane proteins are formed by tethering His-tagged proteins to a nickel nitrilo-triacetic acid (Ni-NTA) modified gold surface and SEIRAS commands molecular sensitivity to probe each step of surface modification. The solid surface used as plasmonic substrate for SEIRAS, can also be employed as an electrode to investigate systems where electron transfer reactions are relevant, like e.g. cytochrome c oxidase or plant-type photosystems. Furthermore, the interaction of these membrane proteins with water-soluble proteins, like cytochrome c or hydrogenase, is studied on the molecular level by SEIRAS. The impact of the membrane potential on protein functionality is verified by monitoring light-dark difference spectra of a monolayer of sensory rhodopsin (SRII) at different applied potentials. It is demonstrated that the interpretations of all of these experiments critically depend on the orientation of the solid-supported membrane protein. Finally, future directions of SEIRAS including cellular systems are discussed. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies.