Antje Quade

Using a Dual Plasma Process to Produce Cobalt-Polypyrrole Catalysts for the Oxygen Reduction Reaction in Fuel Cells II. Analysing the Chemical Structure of the Films

The chemical structure of cobalt--polypyrrole -- produced by a dual plasma process -- is analysed by means of X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption spectroscopy (NEXAFS), X-ray diffraction (XRD), energy-dispersive X-Ray spectroscopy (EDX) and extended x-ray absorption spectroscopy (EXAFS).It is shown that only nanoparticles of a size of 3\,nm with the low temperature crystal structure of cobalt are present within the compound. Besides that, cobalt--nitrogen and carbon--oxygen structures are observed. Furthermore, more and more cobalt--nitrogen structures are produced when increasing the magnetron power. Linking the information on the chemical structure to the results about the catalytic activity of the films -- which are presented in part I of this contribution -- it is concluded that the cobalt--nitrogen structures are the probable catalytically active sites. The cobalt--nitrogen bond length is calculated as 2.09\,\AA\ and the carbon--nitrogen bond length as 1.38\,\AA.

Osteoblast Behavior In Vitro in Porous Calcium Phosphate Composite Scaffolds, Surface Activated with a Cell Adhesive Plasma Polymer Layer

Synthetic materials such as bone substitutes are permanently under development for applications in orthopedic and trauma surgery. Our porous scaffolds were produced from ß-tricalcium phosphate (TCP) using the three dimensional (3D)-printing technology. After sintering the porosity and the pore size of the 3D printed scaffolds reached nearly 50 % and 500 µm, respectively. TCP scaffolds were additionally stabilized by infiltration with polylactic acid (PLA). Because PLA usually impeded cell adhesion we activated the composite surface with plasma polymerized allylamine in a low temperature plasma process. For cell investigations inside the scaffold we used a module system, where two porous discs can be horizontally fixed within a clamping ring. Thereby a 3D cell culture module with four levels and a maximal height of 10 mm was generated. Human MG-63 osteoblasts (ATCC) were seeded apically and placed in serum-containing DMEM. After 14 days of a static cell culture the cell ingrowth and mobility was analyzed by scanning electron microscopy. Osteoblasts initial adhesion and short time occupation of the surface is significantly improved on plasma polymer activated TCP surfaces, which could be a precondition for an enhanced colonization inside a calcium phosphate scaffold. Interestingly, the plasma functionalization of the pure TCP scaffold was possible and successful concerning cell acceptance.

Using a Dual Plasma Process to Produce Cobalt-Polypyrrole Catalysts for the Oxygen Reduction Reaction in Fuel Cells I. Characterization of the Catalytic Activity and Surface Structure

A new dual plasma coating process to produce platinum-free catalysts for the oxygen reduction reaction in a fuel cell is introduced. The catalysts thus produced were analysed with various methods. Electrochemical characterisation was carried out by cyclic voltammetry, rotating ring- and rotating ring-disk electrode. The surface porosity of the different catalysts thus obtained was characterised with the nitrogen gas adsorption technique and scanning electron microscopy was used to determine the growth mechanisms of the films. It is shown that catalytically active compounds can be produced with this dual plasma process. Furthermore, the catalytic activity can be varied significantly by changing the plasma process parameters. The amount of H

Comparison of Nonthermal Plasma Processes on the Surface Properties of Polystyrene and Their Impact on Cell Growth

_2

Vanadia–titania multilayer nanodecoration of carbon onions via atomic layer deposition for high performance electrochemical energy storage

O

Comparative study of plasma-treated non-precious catalysts for oxygen and hydrogen peroxide reduction reactions

_2

Continuous cellularization of calcium phosphate hybrid scaffolds induced by plasma polymer activation.

produced was calculated and shows that a 2 electron mechanism is predominant. The plasma coating mechanism does not significantly change the surface BET area and pore size distribution of the carbon support used. Furthermore, scanning electron microscopy pictures of the produced films are presented and show the preference of columnar growth mechanisms. By using different carbons as the support it is shown that there is a strong dependence of the catalytic activity that is probably related to the chemical properties of the carbon.

DC Operated Air Plasma Jet for Antimicrobial Copper Coatings on Temperature Labile Surfaces

The initial adhesion and spreading of cells are crucial factors for the successful performance of a synthetic biomaterial used for cell culture disposables or human medical devices (e.g., implants). Surface properties which allow the control of the attachment of cells are decisive for the acceptance of the provided material. Hence, different surface preparation techniques are used to equip surfaces with functional groups to improve initial surface interactions. In this paper, polystyrene (PS) surfaces were modified by using different nonthermal plasma processes. In particular, low-pressure plasma and atmospheric-pressure plasma were applied to modify surfaces or to deposit thin films on surfaces. Furthermore, the behaviors of human osteoblastic cells with respect to cell viability and cell growth on differently plasma treated PS surfaces are investigated. A comparison is made between plasma-grafted PS and commercially available PS-such as tissue-culture PS and Primaria. The cell studies were accompanied by surface analysis comprising atomic force microscopy, determination of surface energies, and X-ray photoelectron spectroscopy measurements. This work demonstrates that the functionalization of PS substrates by applying low-pressure and atmospheric-pressure plasma processes are equally effective in the improvement of cell attachment and proliferation. Furthermore, it is shown that the enhanced metabolic activity and spreading behavior of osteoblastic cells correlate well with an increase in surface wettability and the introduction of polar oxygen- and/or nitrogen-containing functional groups after plasma treatment.

Atomic Layer-Deposited Molybdenum Oxide/Carbon Nanotube Hybrid Electrodes: The Influence of Crystal Structure on Lithium-Ion Capacitor Performance

Atomic layer deposition has proven to be a particularly attractive approach for decorating mesoporous carbon substrates with redox active metal oxides for electrochemical energy storage. This study, for the first time, capitalizes on the cyclic character of atomic layer deposition to obtain highly conformal and atomically controlled decoration of carbon onions with alternating stacks of vanadia and titania. The addition of 25 mass% TiO2 leads to expansion of the VO2 unit cell, thus greatly enhancing lithium intercalation capacity and kinetics. Electrochemical characterization revealed an ultrahigh discharge capacity of up to 382 mA h g−1 of the composite electrode (554 mA h g−1 per metal oxide) with an impressive capacity retention of 82 mA h g−1 (120 mA h g−1 per metal oxide) at a high discharge rate of 20 A g−1 or 52C. Stability benchmarking showed stability over 3000 cycles when discharging to a reduced potential of −1.8 V vs. carbon. These capacity values are among the highest reported for any metal oxide system, while in addition, supercapacitor-like power performance and longevity are achieved. At a device level, high specific energy and power of up to 110 W h kg−1 and 6 kW kg−1, respectively, were achieved when employing the hybrid material as anode versus activated carbon cathode.

Antimicrobial copper-coatings on temperature labile surfaces deposited with a DC plasma jet operated with air

The performance of plasma-treated non-precious catalysts is discussed in the light of their application for oxygen and hydrogen peroxide reduction reactions. Six different Fe and Co porphyrins and phthalocyanines were used as precursors. The precursors were mixed with a carbon support and treated with an Ar-, N2- and Ar : O2-radio frequency (RF) plasma to obtain carbon supported Fe–N/C or Co–N/C catalysts. Additionally, the effect of plasma pretreatment of the catalysts support was studied. The electrochemical properties of these catalysts were evaluated by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques (ORR) and for hydrogen peroxide (H2O2) reduction reaction. The difference in activity of the porphyrin-based catalyst treated by plasma and the Pt catalyst was less for H2O2 reduction reaction than for ORR. Selected samples were also tested in a HCOOH/H2O2 proton exchange membrane fuel cell (PEMFC). The maximum power of the HCOOH/H2O2 fuel cell with plasma treated catalyst was 1.4-fold higher than that of the fuel cell with noble metal based catalysts (Pt/C). The catalysts were also characterized in terms of their morphology, structure and composition by atomic force microscopy (AFM), attenuated total reflection infrared spectroscopy (ATR FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). A correlation was found between the activity and concentration of nitrogen on the surface of the catalysts. The AFM investigations revealed morphological changes which accompanied the transformation of the catalyst precursor into the catalytic material.