Oxide cathodes electrolyte oxidation

Sol-gel technique has been used to deposit solid electrolyte layers within the LSM cathode. The layer deposited near the cathode/electrolyte interface can provide ionic path for oxide ions, spreading reaction sites into the electrode. Deposition of YSZ or samaria-doped ceria (SDC, Smo.2Ceo.8O2) films in the pore surface of the cathode increased the area of TPB, resulting in a decrease of cathode polarization and increase of cell performance [15],... 

This presentation reports some studies on the materials and catalysis for solid oxide fuel cell (SOFC) in the author s laboratory and tries to offer some thoughts on related problems. The basic materials of SOFC are cathode, electrolyte, and anode materials, which are composed to form the membrane-electrode assembly, which then forms the unit cell for test. The cathode material is most important in the sense that most polarization is within the cathode layer. The electrolyte membrane should be as thin as possible and also posses as high an oxygen-ion conductivity as possible. The anode material should be able to deal with the carbon deposition problem especially when methane is used as the fuel. 

The work on the electrochemical generation of a solution of ceric sulphate from slurry of cerous sulphate in 1-2 M sulphuric acid was abandoned by BCR due to difficulties encountered in handling slurried reactants. A 6kW pilot reactor operated at 50 °C using a Ti plate anode and a tungsten wire cathode (electrolyte velocity about 2ms 1) produced 0.5 M Ce(S04)2 on the anode with a current efficiency of 60%. The usefulness of Ce(IV) has been limited by the counter anions [131,132], Problems include instability to oxidation, reactivity with organic substrates and low solubility. Grace found that use of cerium salts of methane sulfonate avoids the above problems. Walsh has summarized the process history, Scheme 6 [133],... 

Cathode In contrast to the anode the cathode operates in an oxidizing environment but, like the anode, it must have high electronic conductivity and a pore structure enabling the gaseous oxidant to reach the cathode/electrolyte interface. 

Complete the concept map using the following tenns reduction, electrodes, electrochemical cells, anode, oxidation, cathode, electrolyte. 

Various materials are used for production of the three main components of a lithium ion battery. Research and development of these materials is where the automotive chemist is severely needed. The main components of the battery are the electrolyte, cathode, and anode. For the cost imperative, graphite is used most often in the anode. The cathode is typically a layered lithium cobalt oxide, lithium iron phosphate, or lithium manganese oxide. Other materials, such as TiS2, have been used [18]. Of course, properties vary depending on the choice of anode, cathode, electrolyte, etc. 

For perovskites that are used in high-temperature applications, such as solid oxide fuel cells that operate above 800°C or so, thermal expansion becomes an important physical property, as mismatch of the thermal expansion of the cell components, cathode, electrolyte and anode, will cause early cell failure. The magnitude of the thermal expansion of many perovskites is rooted in the thermal behaviour of the BXg octahedra and is associated with octahedral tilt, distortion and the bonding between the B-cation and the surrounding anions. These are all susceptible to modification as the temperature rises and can contribute to anomalies in thermal expansion characteristics. 

Chemically and thermally resistant steels contain considerable quantities of chromium (more than 20%). On the side of the oxygen, cathode metalhc chromium is oxidized to Cr203. Depending on the temperature and oxygen partial pressure, this oxide may further oxidize to volatile compounds CrOg and Cr02(0H)2, which could then settle at the cathode/electrolyte interface and hinder oxygen reduction. Such an evaporation of chromium is the basic difficulty in the use of metallic bipolar plates. 

A SEM micrograph of the cathode/electrolyte interface and preliminary results on the electrochemical activity of YSZ electrolyte-supported SOFCs containing Ni-YSZ anode and a LSCF-SDC composite cathode are shown in Fig. 14. As it can be seen in Fig. 14(a), the composite film not only has good adhesion to the electrolyte, but also possesses a porous microstructure which is required for the oxidant electrochemical reduction. It indicates that such a composite film can have a good performance as SOFC cathode. By the LSV technique, qualitative information about electrochemical activity of this SOFC was acquired. The power density curves (Fig. 14b) revealed that maximum power densities were 19, 26, 36 and 46 mW/cm2 at 800, 850, 900 and 950 °C. It is possible to compare these first results with literature data and safely state that the LSCF-SDC cathode composite is qualitatively better than other plain standard materials or cathode composites already reported. It should also be mentioned that the result obtained at 800 °C is similar to that reported by Mucdllo et al (Mucdllo et al., 2006) for a SOFC single cell with LSM-YSZ cathode, Ni-YSZ anode and 70 pm... 

The cell potential is the operating potential of the cell, which is a manifestation of the collected differences in the electric potential between the various phases in the cell [82]. Assuming H2 oxidation as the only charge transfer reaction, the potential difference across the anode-electrolyte interface and cathode-electrolyte interface without taking into account the... 

The basic components of the SOFC are the anode, the cathode and the electrolyte, as shown in Fig. 10.1. They are together referred to as the membrane electrode assembly (MEA). Fuel (hydrogen) is supplied to the anode side and air is supplied to the cathode side. At the cathode-electrolyte interface, oxygen molecules accept electrons coming from the external circuit to form oxide ions. The solid electrolyte allows only oxide ions to pass through. At the anode-electrolyte interface, hydrogen molecules present in the fuel react with oxide ions to form steam, and electrons get released. As a result of the potential difference set up between anode and cathode... 

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... 

Such a situation may arise as a result of a continuous application of the electric current over a long period of time. As a matter of fact, electrochemical reactions take place at the electrodes, and in the absence of depolarizing species, water molecules are oxidized at the anodes and reduced at the cathodes (electrolytic reactions), with formaticHi of protons and hydroxyl anions, respectively. Once formed, these species tend to migrate under the effect of both potential and concentration gradients, allowing the development of an acidic front fmm the anode towards the cathode and of an alkaline frrnit in the opposite directimi (since the icaiic molrility of BF ions is 1.75 times that of OH i(Mis, the movement of protons will dominate the system chemistry). 

A third generation system, as shown in Figure 5.62. It was composed of a microchannel oxidative steam reformer, which was supplied with water and air from the cathode off-gas. It was operated at a S/Cratio 1.9andanO/Cratioof0.15. The microchannel reformer was internally coupled to a catalytic burner, which was supplied with residual hydrogen from the fuel cell anode and cooling air from the cathode. The medium temperature fuel cell (operated between 400 and 600 °C) was cooled by air and worked with a metallic membrane. The membrane had the additional function of an anode electrode. BaCeo.g03 served as the cathode electrolyte. 

Anodic reactions occur on the anode-electrolyte interface according to eq. (7.3) having a standard potential of = -1.23 V (Table 2.2) for the oxidation reaction to proceed. The electrons produced by eq. (7.3) are driven through the external circuit by the D.C. power and are consumed by the cathodic reactions at the cathode-electrolyte interfaces and proceeds according to the reaction defined by eq. (7.5)... 

---