N-doped carbon, a promising alternative to Pt catalyst for oxygen reduction reactions (ORRs) in acidic media, is modified in order to increase its catalytic activity through the additional doping of B and P at the carbon growth step. This additional doping alters the electrical, physical, and morphological properties of the carbon. The B-doping reinforces the sp(2)-structure of graphite and increases the portion of pyridinic-N sites in the carbon lattice, whereas P-doping enhances the charge delocalization of the carbon atoms and produces carbon structures with many edge sites. These electrical and physical alternations of the N-doped carbon are more favorable for the reduction of the oxygen on the carbon surface. Compared with N-doped carbon, B,N-doped or P,N-doped carbon shows 1.2 or 2.1 times higher ORR activity at 0.6 V (vs RHE) in acidic media. The most active catalyst in the reaction is the ternary-doped carbon (B,P,N-doped carbon), which records -6.0 mA/mg of mass activity at 0.6 V (vs RHE), and it is 2.3 times higher than that of the N-doped carbon. These results imply that the binary or ternary doping of B and P with N into carbon induces remarkable performance enhancements, and the charge delocalization of the carbon atoms or number of edge sites of the carbon is a significant factor in deciding the oxygen reduction activity in carbon-based catalysts.

Binary and Ternary Doping of Nitrogen, Boron, and Phosphorus into Carbon for Enhancing Electrochemical Oxygen Reduction Activity

Freestanding CrNx and Cr1 − xAlxN films with two different Al atomic percentages with respect to the metal sublattice (x = 0.23 and x = 0.60) were produced by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The dynamic oxidation behavior of the films has been characterized by thermal analysis using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The structure of the films at different thermal-annealing temperatures were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in an effort to understand different phase transitions and oxidation reactions observed on the DSC curves. The peak temperatures of the main exothermic/endothermic oxidation reactions in the DSC signals at different heating rates were applied to the Kissinger model for determination of activation energies. The mechanical properties of the films at different heat-annealing states were measured by nano-indentation. It was found that the CrNx films oxidized in air after 600 °C by the dissociation of fcc (face center cubic)-CrN to h(hexagonal)-Cr2N and nitrogen and, after 900 °C by the dissociation of h-Cr2N to Cr and nitrogen in the film. The addition of Al to CrN film can further improve the oxidation resistance, especially for the high temperature above 800 °C. The oxidation degradation in two Cr-Al-N films started with dissociation of fcc-CrAlN to h-Cr2N and nitrogen in the film. The presence of thermally stable Al–N bonding in the fcc-CrAlN structure can suppress the reduction of nitrogen in the film. A dense (Cr,Al)2O3 layer (either amorphous or crystalline) formed at early oxidation stage (

A study of the oxidation behavior of CrN and CrAlN thin films in air using DSC and TGA analyses

A new strategy for enhancing the oxygen reduction reaction (ORR) activity of carbon-based catalysts in acidic media is proposed and characterized; the strategy consists in modifying the ORR through dual doping of nitrogen and phosphorus into the carbon. The P, N-doped carbon is prepared via pyrolysis of a mixture composed of dicyandiamide (DCDA), phosphoric acid, cobalt chloride, and iron chloride at 900 °C under an Ar atmosphere. The P-doping induces an uneven surface with many open edged sites in the carbon morphology and increases the carbon surface area from 108.1 to 578.8 m2 g−1. The XRD, XPS-C1s, and Raman spectroscopy results reveal that the crystallinity and degree of the sp2-carbon network decrease and the number of defect sites of the carbon increase as the amount of P-doping increases. All catalysts demonstrated similar proportions of N-doping types regardless of the P-doping amount: pyridinic-N and graphitic-N were dominant phases in the carbon lattice. In the ORR, the onset potential of the prepared catalysts was 0.6 V (vs. Ag/AgCl) in 1 M HClO4. The N-doped carbon records −0.69 mA mg−1 of mass activity at 0.5 V (vs. Ag/AgCl), but additional P-doping results in an increase of activity (−2.88 mA mg−1) that is more than fourfold that produced without the additional P-doping. Moreover, additional P-doping also modifies the ORR pathway, as the N-doped carbon induces more than 10% of H2O2; however, the P, N-doped carbon produced below 4% of H2O2 during the ORR.

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Phosphorus–nitrogen dual doped carbon as an effective catalyst for oxygen reduction reaction in acidic media: effects of the amount of P-doping on the physical and electrochemical properties of carbon

Comparative tribological behaviors of TiN, CrN and MoNCu nanocomposite coatings

Nanocomposite coatings including CrN/Ag, ZrN/Ag, TiN/Ag and TiN/Cu with varying silver or copper contents were produced by co-deposition in a dual pulsed magnetron sputtering system. The compositions and structures of the coatings were characterised using energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM), and the physical and tribological properties were assessed by means of nanoindentation and thrust washer wear testing. Although increasing silver or copper content provided a reduction in the coefficient of friction, this was accompanied by reductions in hardness for all the coatings and wear resistance for some of the coatings. Zones of inhibition were used to determine the extent of silver ion release from the coating surfaces, and a NBT (nitro-blue tetrazolium) redox dye was used to determine the antimicrobial effectiveness of the coatings following incubation. The microorganisms tested were Pseudomonas aeruginosa and Staphylococcus aureus. For the NBT assays, significant reductions in the number of viable cells were observed with increasing Ag or Cu content, compared to the ‘pure’ nitride surfaces. Whilst no zones of inhibition were observed for S. aureus, on any of the surfaces, the diameter of the ‘kill’ zones generally increased with increasing silver content for P. aeruginosa.

Comparison of the tribological and antimicrobial properties of CrN/Ag, ZrN/Ag, TiN/Ag, and TiN/Cu nanocomposite coatings

Ti-Cu-N nanocomposite films deposited by arc ion plating and magnetron sputter hybrid system with various copper contents. The microstructure and mechanical properties of Ti-Cu-N superhard nanocomposite films depend on the Cu concentration. In X-ray diffraction (XRD) analysis, intensity of TiN (111) and TiN (220) peak decreased and peak broadness increased with increasing the copper contents and Cu peak was not detected. The grain size of films decreased with increasing at%Cu and Transmission Electron Microscopy (TEM) analysis also showed that Ti-Cu-N film containing 1.5at%Cu was composed of very fine (

The effect of metal composition on the structure and properties of Ti-Cu-N superhard nanocomposite coatings

High-temperature oxidation of magnetron-sputtered Cr–N-coated steels

PURPOSE: A carbon nitride coating synthesized on parts for automobile engine is provided which has superior mechanical properties compared to conventional coating by applying carbon nitride (CNx) coating onto the parts for automobile engine, and a coating apparatus for realizing high synthesis speed is provided. CONSTITUTION: In a coating synthesized on a material to be coated selected from parts for automobile engine, the carbon nitride coating synthesized on the parts for automobile engine is characterized in that the coating is a carbon nitride (CNx) layer obtained by adding nitrogen to carbon. In an apparatus comprising a vacuum housing(31) in which a material to be coated is subject to coating treatment, and a vacuum pump(32) installed at the outer side of the vacuum housing to provide internal pressure of the vacuum housing, the coating apparatus comprises magnetron sources(33,34) which are installed at both sides of the vacuum housing oppositely directed to each other, and on any one side of which a solid phase carbon target for synthesizing carbon nitride (CNx) thin film is mounted; a rotational jig(35) which transfers the material to be coated so that the material to be coated passes by the front side of the magnetron sources in the vacuum housing, and which is insulated with the vacuum housing so that a DC bias voltage (-) is impressed to the rotational jig; and a gas control part(36) which is arranged at the outer side of the vacuum housing and connected to the inner part of the vacuum housing, and which controls supply of flow rate of N2 and Ar gases for synthesizing the carbon nitride (CNx) thin film, wherein a material selected from Cr, Si, W and Ti is mounted on the other side of the magnetron sources as a target to relieve cohesive force and residual stress of coating.

Hyun S. Myung

Papers

The effect of metal composition on the structure and properties of Ti-Cu-N superhard nanocomposite coatings

High-temperature oxidation of magnetron-sputtered Cr–N-coated steels

Carbon nitride coating synthesized on parts of automobile engine and coating apparatus