Cathode/electrolyte interface separators

SOFC is composed of a dense oxygen ion-conducting electrolyte separating a porous anode and a porous cathode as a single cell. Electrical intercoruiections can be used to combine the individual cells to produce a stack. The ceU is operated by supplying oxygen at the cathode which is reduced at the cathode-electrolyte interface. At the same time, fuel gas is fed to the anode and it is oxidized at... 

Another comparison between Figures 2.1 and 8.1 points to a more basic difference between electrodeposition and electroless deposition. There are two electrodes in Figure 2.1 a cathode and an anode. Here two separate electron-transfer reactions occur at two spatially separated electrode-electrolyte interfaces. At the cathode a reduction reaction occurs [Eq. (8.1)], and at the anode an oxidation reaction occurs for example,... 

In this type of cell both electrodes are immersed in the same constant pH solution. An illustrative cell is [27,28] n-SrTiOs photoanode 9.5-10 M NaOH electrolyte Pt cathode. The underlying principle of this cell is production of an internal electric field at the semiconductor-electrolyte interface sufficient to efficiently separate the photogenerated electron-hole pairs. Subsequently holes and electrons are readily available for water oxidation and reduction, respectively, at the anode and cathode. The anode and cathode are commonly physically separated [31-34], but can be combined into a monolithic structure called a photochemical diode [35]. 

It must be noted that the Comsol Multiphysics simulation does not take into account the electrochemical reactions occurring at the cathode-electrolyte and electrolyte-anode interfaces, with corresponding activation losses (which will be treated separately in Section 6.2.2). 

Electrochemical energy storage and conversion systems described in this chapter comprise batteries and fuel cells [6-11], In both systems, the energy-supplying processes occur at the phase boundary of the electrode-electrolyte interface moreover, the electron and ion transports are separate [6,8], Figures 8.1 and 8.2 schematically illustrate the electron and ion conductions in both the electrodes and the electrolyte in Daniel and fuel cells. The production of electrical energy by the conversion of chemical energy by means of an oxidation reaction at the anode and a reduction reaction at the cathode is also described. 

Since the charge transfer across a semiconductor-electrolyte interface can only occur via the conduction or valence band, the processes via the two bands have to be treated separately. In general anodic and cathodic currents are given by equations similar to... 

If the whole semiconductor/electrolyte interface is illuminated uniformly, both conjugate reactions proceed at the same rate over the same areas on the interface. The stationary potential of an illuminated semiconductor is thus a mixed potential. If the surface of a semiconductor, homogeneous in its composition and properties, is illuminated nonuniformly, in the illuminated and nonillumi-nated areas conditions will not be identical for electrochemical reactions. Here the conjugate reactions appear to be spatially separated, so that we can speak about local anodes and cathodes. This situation is deliberately created, for example, for selective light-sensitive etching of semiconductors (see Section V.2). 

The model for atmospheric corrosion tmder high chloride concentration su ested by Kamimura et al. [32] is based on the separation of cathode and anode sites under the rust and the thin electrolyte. The pH at the anode compartment is affected by the chloride ion concentration and decreased to 1.5 by the hydrolysis of ferric ions and the formation of P-FeOOH. Chloride ions accumrrlate at the anode site and initiate the oxidation of ferrous ions to ferric ions. Accumulated chloride ions increase ferric ion solubility in the electrolyte and accelerate the hydrolysis of ferric ions, causing the pH at the anode to decrease. Low pH at the metal-electrolyte interface accelerated the formation of P-FeOOH. The atmospheric corrosion process is summarized as follows ... 

Fuel cells consist of two electrodes, anode and cathode, which are separated by an electrolyte. The anode provides an interface between the fuel and the electrolyte, while the cathode provides an interface between the oxygen and the electrolyte. The electrodes contain catalysts for the oxidation of fuel and reduction of oxygen. At the anode, the oxidation reaction produces free proton (H+) and electron e". The proton travels to the cathode via the electrolyte, while the electron is harnessed as direct current via an external circuit. In addition to completing the electrical circuit by transporting ions between the electrodes, the electrolyte also acts as the separator between the fuel and the oxidant. 

Mesoscale modeling of SOFCs focuses on modeling the transport and reactions of gas species in the porous microstructures of the electrodes [3, 34, 56-59]. In these models, the porous microstructure is explicitly resolved, which negates the need for the effective parameters of macroscale models. The transport and reactions of species in mesoscale models are described by the species [Eq. (26.1)], momentum [Eq. (26.5)], and energy [Eq. (26.7)] conservation equations, which are solved at the pore scale. At the pore scale, the conservation equations are solved in two separate domains the solid domain of the tri-layer and the gas domain of the pore space within the tri-layer. Mesoscale models aim to understand the effects of microstructure and local conditions near the electrode-electrolyte interface on the SOEC physics and performance. These models have been used to investigate a number of design and degradation issues in the electrodes such as the effects of microstructure on the transport of species in the anode [19, 56] and the reactions of chromium contaminants in the cathode [34]. 

---