Diffusion of hydrogen and oxygen

Keywords titanic powders, diffusion of hydrogen and oxygen, oxides, hydrides in titanic... 

In addition to these two main reactions, there are some other processes having an impact on the electrode behavior. The surface mobility of adsorbed species in the catalytic layer is relevant to analyze the performance and degradation of the fuel cell membrane-electrode assembly. This study is not an easy task and, therefore, these phenomena have been scarcely explored. The diffusion of hydrogen and oxygen adsorbed species is particularly relevant for the performance and stability of PEMFC electrodes. 

Example 5.7 Estimation of Diffusivity of Hydrogen and Oxygen in Water Vapor Estimate the diffusivity of hydrogen in water vapor and oxygen in water vapor at 1 atm and 307 K and compare with experimental data in Table 5.4. 

The calculated diffusion constants of hydrogen and oxygen atoms are shown in Figure 9. The inset plot shows the equation of state for this isotherm for both L and S simulations. The two results are virtually identical up until 2.6 g/cc. At 34 GPa (2.0 gIcc), the hydrogen atom diffusion constant has achieved values associated with superionic conductivity (greater than... 

The selection of the diffusion material is a subject of considerable difficulty, if the porosity of the material is too great no diffusion takes place, but the gas passes through the material without any appreciable separation taking place. Thus, if a mixture of hydrogen and oxygen is passed through a fine capillary tube, the gas... 

Systems in which diffusion or chemical reaction is taking place at an appreciable rate are not in thermodynamic equilibrium, and consequently their state cannot be completely specified in a simple manner. Certain systems which are not in true equilibrium may nevertheless be treated by thermodynamic methods, provided the approach to equilibrium is so slow as to be undetectable over a considerable period of time. An instance of this type is represented by a mixture of hydrogen and oxygen gases under normal conditions of temperature and pressure. As mentioned earlier, reaction should take place with the formation of liquid water,... 

In ambipolar diffusion of protons and oxygen ions, the two types of ions move in the same direction for charge compensation, and the net result is permeation of water. If we also have electronic transport, then the transport of hydrogen and oxygen ions may be de-coupled. They may move in the same direction or in opposite directions and at different ratios. 

Diffusion. Data for selfdiffusion, diffusion of tracer elements and of hydrogen and oxygen are shown in Tables 3.1-156, 3.1-158, 3.1-217. 

The focus of this chapter is on analyzing and modeling the microstructure of gas diffusion layers (GDLs) in polymer electrolyte membrane fuel cells (PEMFCs). GDLs are fiber-based materials and one of their main tasks is the transportation of hydrogen and oxygen towards the electrodes where the electrochemical reaction takes place, that is, electricity is generated and the transport of the byproduct water from the electrode towards the channel is accomplished [1]. 

The diffusion coefficients of hydrogen and oxygen in the polymer electrolyte are evaluated as follows [14] ... 

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