Electroreduction of CO2 on Au(310)@Cu High-index Facets.

The chemical selectivity and faradaic efficiency of high-index Cu facets for the CO2 reduction reaction (CO2 RR) is investigated. More specifically, shape-controlled nanoparticles enclosed by Cu {hk0} facets are fabricated using Cu multilayer deposition at three distinct layer thicknesses on the surface facets of Au truncated ditetragonal nanoprisms (Au DTPs). Au DTPs are shapes enclosed by 12 high-index {310} facets. Facet angle analysis confirms DTP geometry. Elemental mapping analysis shows Cu surface layers are uniformly distributed on the Au {310} facets of the DTPs. The 7 nm Au@Cu DTPs high-index {hk0} facets exhibit a CH4 : CO product ratio of almost 10 : 1 compared to a 1 : 1 ratio for the reference 7 nm Au@Cu nanoparticles (NPs). Operando Fourier transform infrared spectroscopy spectra disclose reactive adsorbed *CO as the main intermediate, whereas CO stripping experiments reveal the high-index facets enhance the *CO formation followed by rapid desorption or hydrogenation.

Impact of Carbon N-Doping and Pyridinic-N Content on the Fuel Cell Performance and Durability of Carbon-Supported Pt Nanoparticle Catalysts.

Cathode catalyst layers of proton exchange membrane fuel cells (PEMFCs) typically consist of carbon-supported platinum catalysts with varying weight ratios of proton-conducting ionomers. N-Doping of carbon support materials is proposed to enhance the performance and durability of the cathode layer under operating conditions in a PEMFC. However, a detailed understanding of the contributing N-moieties is missing. Here, we report the successful synthesis and fuel cell implementation of Pt electrocatalysts supported on N-doped carbons, with a focus on the analysis of the N-induced effect on catalyst performance and durability. A customized fluidized bed reduction reactor was used to synthesize highly monodisperse Pt nanoparticles deposited on N-doped carbons (N-C), the catalytic oxygen reduction reaction activity and stability of which matched those of state-of-the-art PEMFC catalysts. Operando high-energy X-ray diffraction experiments were conducted using a fourth generation storage ring; the light of extreme brilliance and coherence allows investigating the impact of N-doping on the degradation behavior of the Pt/N-C catalysts. Tests in liquid electrolytes were compared with tests in membrane electrode assemblies in single-cell PEMFCs. Our analysis refines earlier views on the subject of N-doped carbon catalyst supports: it provides evidence that heteroatom doping and thus the incorporation of defects into the carbon backbone do not mitigate the carbon corrosion during high-potential cycling (1-1.5 V) and, however, can promote the cell performance under usual PEMFC operating conditions (0.6-0.9 V).

Ionomer distribution control in porous carbon-supported catalyst layers for high-power and low Pt-loaded proton exchange membrane fuel cells.

The reduction of Pt content in the cathode for proton exchange membrane fuel cells is highly desirable to lower their costs. However, lowering the Pt loading of the cathodic electrode leads to high voltage losses. These voltage losses are known to originate from the mass transport resistance of O2 through the platinum-ionomer interface, the location of the Pt particle with respect to the carbon support and the supports' structures. In this study, we present a new Pt catalyst/support design that substantially reduces local oxygen-related mass transport resistance. The use of chemically modified carbon supports with tailored porosity enabled controlled deposition of Pt nanoparticles on the outer and inner surface of the support particles. This resulted in an unprecedented uniform coverage of the ionomer over the high surface-area carbon supports, especially under dry operating conditions. Consequently, the present catalyst design exhibits previously unachieved fuel cell power densities in addition to high stability under voltage cycling. Thanks to the Coulombic interaction between the ionomer and N groups on the carbon support, homogeneous ionomer distribution and reproducibility during ink manufacturing process is ensured.

High Electromagnetic Field Enhancement of TiO2 Nanotube Electrodes.

We present the fabrication of TiO2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface-enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochrome b5 were observed upon covalent immobilization of the protein matrix on the TiO2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 °C. For the first time, such high values are reported for non-directly surface-interacting probes, for which the involvement of charge-transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode.

Fate of leaf litter deposits and impacts on oxygen availability in bank filtration column studies.

Degradation of particulate organic carbon (POC) such as leaf litter might deplete dissolved oxygen within the upper layers of bank filtration, an efficient and robust barrier for pathogens and for various organic micro-pollutants (OMP) in water supply systems worldwide. The degradation of OMP during bank filtration depends on the redox conditions. The present study aimed at identifying the impacts and fates of different local leaves on the oxygen consumption and the possible biological degradation of indicator OMP. Oxygen concentrations initially decreased within the columns from around 8 mg/L in the influent to low concentrations indicating extensive consumption within a short travel distance. Still a substantial oxygen consumption was observed after 250 days. OMP concentrations were not significantly affected by the microbial processes. A layer of calcium carbonate crystallites was observed on the POC layer. Some leaf fragments appeared to be persistant towards degradation and the carbon content relative to nitrogen and sulfur contents decreased within 250 days. The results demonstrate that trees at bank filtration sites might have a strong long-term impact on the subsurface redox conditions.

Microporous polymer network films covalently bound to gold electrodes.

Covalent attachment of a microporous polymer network (MPN) on a gold surface is presented. A functional bromophenyl-based self-assembled monolayer (SAM) formed on the gold surface acts as co-monomer in the polymerisation of the MPN yielding homogeneous and robust coatings. Covalent binding of the films to the electrode is confirmed by SEIRAS measurements.

Adsorption isotherms of cellulose-based polymers onto cotton fibers determined by means of a direct method of fluorescence spectroscopy.

We present a novel method for the measurement of polymer adsorption on fibers by employing fluorescently labeled polymers. The method itself can be used for any compound that either shows fluorescence or can be labeled with a fluorescent dye, which renders it ubiquitously applicable for adsorption studies. The main advantage of the method is that the choice of adsorbent is not limited to flat surfaces, thereby allowing the investigation of fibrous and porous systems. As an example of high interest for application we determined the adsorption isotherms of various polysaccharide-based polymers with different charges and different substituents on cotton fibers. These experiments show that the extent of adsorption depends not only on the charge conditions but also very much on the specific interactions between the polymer and fiber. For instance, the cationic hydroxyethyl cellulose can become bound to an extent similar to that of the anionic alginate, while the anionic carboxymethyl cellulose of similar charge density adsorbs much less under these conditions. This shows that the adsorption of polymers depends subtly on the details of the interaction between the polymer and fiber but can be determined with good precision with our direct fluorescence method.

Stability of polylactic acid particles and release of fluorochromes upon topical application on human skin explants.

Particle-based drug delivery systems allow the controlled and targeted release of incorporated active compounds to the skin and are promising tools to improve the efficacy of topical therapies. In this study we investigated the stability and release properties of biodegradable polylactic acid (PLA) particles upon topical application on human skin explants. PLA particles loaded with the hydrophilic fluorochrome 4-Di-2-Asp (DiAsp-PLA) were compared to PLA particles loaded with the lipophilic fluorochrome Bodipy 630/650 (BP-PLA). Changes of the particle morphology after their incubation on skin surface were investigated by means of electron microscopy while fluorescence microscopy and flow cytometry were used to evaluate particle penetration in hair follicles and fluorochrome release. We found that BP-PLA particles released rapidly the loaded fluorochrome and lost the particulate morphology within a few hours after application on skin surface. On the contrary, DiAsp-PLA particles maintained the particulate morphology, accumulated in hair follicles, and allowed a constant release of the incorporated fluorochrome for up to 16 h. These results show that, once applied to skin surface, PLA particles release the incorporated fluorochromes in a time-dependent manner and suggest the perspective to modulate particle stability and release properties by incorporating excipients with different degree of lipophilicity.

The influence of polymers, surfactants and salt on the fine structure of cotton revealed by SANS.

Cotton is the most abundantly employed material for the production of fabrics. Therefore it is very interesting to know the influence of compounds commonly in contact with cotton during the washing process, on its mesoscopic structure. Small angle neutron scattering (SANS) is able to monitor structural changes in the range of 1 to a few 100 nm, making it a powerful tool to observe such changes. For that purpose we studied the change of fibre structure if exposed to low concentrations of polymer or surfactant, as they are relevant in the washing process. An interesting observation is that for the effectively available surface of cotton fibres their nanometric structure appears to be the central aspect. However, this local structure is only little affected by the presence of anionic surfactant. The same applies to a variety of polymers and only for the addition of a cationically modified cellulose a substantial increase of the thickness of the locally present rod-like structures by ~30% is observed.

Novel Au-Ag hybrid device for electrochemical SE(R)R spectroscopy in a wide potential and spectral range.

A nanostructured gold-silver-hybrid electrode for SER spectroelectrochemistry was developed which advantageously combines the electrochemical properties and chemical stability of Au and the strong surface enhancement of (resonance) Raman scattering by Ag. The layered device consists of a massive nanoscopically rough Ag electrode, a thin (2 nm) organic layer, and a ca. 20 nm thick Au film that may be coated by self-assembled monolayers for protein adsorption. The SERR-spectroscopic and electrochemical performance of this device is demonstrated using the heme protein cytochrome c as a benchmark model system, thereby extending, for the first time, SE(R)R studies of molecules on Au surfaces to excitation in the violet spectral range. The enhancement factor is only slightly lower than for Ag electrodes which can be rationalized in terms of an efficient transfer of plasmon resonance excitation from the Ag to the Au coating. This mechanism, which requires a thin dielectric layer between the two metals, is supported by theoretical calculations.