Oxygen carbon-based materials

Carbon-based materials have also been widely used as cathodes in indirect electrolyses of organics generating in situ hydrogen peroxide, by two-electron reduction of oxygen on the cathode surface ... 

Surface functionality and oxygen concentration can influence chemical properties of carbon-based materials in aquatic environments, including surface potential, pH, surface reactivity, and sorption properties (60). Since most of the atoms in CNTs are surface atoms the effects of surface chemistry can be expected to have a large impact on the fate and transport of CNTs in aqueous environments. Smface chemistry is thought to be the primary factor regulating biological toxicity and compatibility of nanomaterials (61), and many potential appHcalions of CNTs are in the biomedical field. 

This chapter focuses on the theoretical modeling studies of ORR catalysts for PEMFC. Theoretical methods, such as density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulation, are presented. Current understanding of ORR mechanism in acidic medium is briefly discussed. Recent theoretical investigations on oxygen reduction electrocatalysts, such as Pt-based catalysts, non-Pt metal catalysts (Pd, Ir, CuCl), and non-precious metal catalysts (transitional metal macrocyclic complexes, conductive polymer materials, and carbon-based materials), are reviewed. The oxygen reduction mechanisms catalyzed by these catalysts are discussed based on the results. 

Pyrolysis is a very common thermochemical decomposition of carbon-based materials at elevated temperatures of700 C in the absence of oxygen. Pyrolysis of plastic waste can yield gases and oils (Williams and lliams 1997 Pinto et al. 1999). The oils can be polymerized back to polymers. 

Q.6.8 Pyrolysis is a chemical recycling process that recovers the chemicals from carbon-based materials by heating materials to very high temperatures, for example, 700°C or higher, in the absence of oxygen. T or F ... 

In the PSA system, compressed air is passed through a column of chemical adsorbent, which is a carbon-based material that essentially traps the oxygen molecules and allows the nitrogen molecule to pass through to the use point. Figure 13.2 shows the process flow of a PSA system, which can produce 98 to 99.5 percent pure nitrogen without the need... 

The activity and stability of catalysts for methane-carbon dioxide reforming depend subtly upon the support and the active metal. Methane decomposes to carbon and hydrogen, forming carbon on the oxide support and the metal. Carbon on the metal is reactive and can be oxidized to CO by oxygen from dissociatively adsorbed COj. For noble metals this reaction is fast, leading to low coke accumulation on the metal particles The rate of carbon formation on the support is proportional to the concentration of Lewis acid sites. This carbon is non reactive and may cover the Pt particles causing catalyst deactivation. Hence, the combination of Pt with a support low in acid sites, such as ZrO, is well suited for long term stable operation. For non-noble metals such as Ni, the rate of CH4 dissociation exceeds the rate of oxidation drastically and carbon forms rapidly on the metal in the form of filaments. The rate of carbon filament formation is proportional to the particle size of Ni Below a critical Ni particle size (d<2 nm), formation of carbon slowed down dramatically Well dispersed Ni supported on ZrO is thus a viable alternative to the noble metal based materials. 

The air gas-diffusion electrode developed in this laboratory [5] is a double-layer tablet (thickness ca.1.5 mm), which separates the electrolyte in the cell from the surrounding air. The electrode comprises two layers a porous, from highly hydrophobic, electrically conductive gas layer (from the side of the air) and a catalytic layer (from the side of the electrolyte). The gas layer consists of a carbon-based hydrophobic material produced from acetylene black and PTFE by a special technology [6], The high porosity of the gas layer ensures effective oxygen supply into the reaction zone of the electrode simultaneously the leakage of the electrolyte through the electrode... 

The catalytic layer of the air electrode is made from a mixture of the same hydrophobic material and porous catalyst [2]. It comprises hydrophobic zones through which the oxygen is transported in gas phase and zones containing catalyst where the electrochemical reduction of oxygen is taking place. It must be noted that the overall structure of the electrode is reproducible when various kinds of carbon-based catalysts are used. 

The isotopic analysis of oxygen in organic materials was first based on catalytic pyrolysis, but in 1987 Santrock and Hayes [668] adapted the Unterzaucher procedure (pyrolysis followed by equilibration with carbon to form CO, which is... 

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