Oxygen transport through electronically

However, for mixed oxygen ion-electron conducting materials the surface processes can become rate limiting for oxygen transport through the membrane rather than bulk diffusion. Under surface reaction we understand the... 

Usually the electronic conduction is found to be predominant, in spite of the fact that the ionic conductivity may also be substantial (see Section V). The examples given in Table 14.2 clearly emphasize the importance of the surface exchange kinetics, relative to diffusion, in limiting overall oxygen transport through the perovskites. 

A fuel cell consists of an ion-conducting membrane (electrolyte) and two porous catalyst layers (electrodes) in contact with the membrane on either side. The hydrogen oxidation reaction at the anode of the fuel cell yields electrons, which are transported through an external circuit to reach the cathode. At the cathode, electrons are consumed in the oxygen reduction reaction. The circuit is completed by permeation of ions through the membrane. 

The electrons are transported through an outer circuit connected to the cathode, where oxygen is reduced to oxygen ions on a similar catalyst system as for the anode ... 

It is well known that the selective transport of ions through a mitochondrial inner membrane is attained when the oxygen supplied by the respiration oxidizes glycolysis products in mitochondria with the aid of such substances as flavin mononucleotide (FMN), fi-nicotinamide adenine dinucleotide (NADH), and quinone (Q) derivatives [1-3]. The energy that enables ion transport has been attributed to that supplied by electron transport through the membrane due to a redox reaction occurring at the aqueous-membrane interface accompanied by respiration [1-5],... 

The logarithmic law is also observed when the oxide film is an electrical insulator such as AI2O3. The transport of electrons through the oxide is mainly due to a space charge which develops between the metal-oxide interface and the oxide-gas interface. The incorporation of oxygen in the surface of the oxide requires the addition of electrons, and if this occurs by a charging process... 

The important processes occurring in a catalyst layer include interfacial ORR at the electrochemically active sites, proton transport in the electrolyte phase, electron conduction in the electronic phase (i.e., Pt/C), and oxygen diffusion through the gas phase, liquid water, and electrolyte phase. 

Figure 7-4. The electron transport chain. Electrons enter from NADH to complex I or succinate dehydrogenase, which is complex II. Electrons derived from glycolysis through the glycerol-3-phosphate shuttle, complex I, and complex II join at coenzyme Q and are transferred to oxygen as shown. As electrons pass through complexes I, III, and IV, protons are transported across the membrane, creating a pH gradient.

The electrode reactions are comprised of the oxidation of hydrogen on Ihe anode (the negative electrode) to hydrated protons with the release ol electrons and on the cathode (the positive electrode) the reaction of oxygen with protons la I unn water vapor with the consumption of electrons. Electrons llow from the anode through the external load to the cathode and the circuit is closed by ionic current transport through the electrolyte. In an acid cell, the current is carried by protons. 

Yttria stabilized zirconia formed by this reaction fills the air electrode pores. The dynamics of this CVD stage has been modeled by Carolan and Michaels [120], who observed that films produced in this manner penetrate the substrate no more than 2-3 pore diameters from the chloride face of the substrate. It has also been shown that the penetration depth is independent of water concentration. The second step of this method is the EVD step. Once pore closure is achieved, the reactants are not longer in contact. Electrochemical semipermeability related to the existence of small electronic conductivity and large gradient of oxygen partial pressure leads to oxygen transport from the steam side to the chloride side through the deposited electrolyte. The electrochemical reactions involved are ... 

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