Cathodes composition/preparation

As an example of a cathode film the (Lag gSrg 2)o.9Mn03 (LSM) per-ovskite will be used for electrode preparation and evaluation. Composite symmetrical and asymmetrical (Lag gSr 2) MnOj-YSZ (LSM-YSZ) structures were prepared on dense YSZ substrate (0.4 mm thick) [21]. The symmetrical cell was used for composite LSM-YSZ and composite LSM-YSZAfSZ electrode overpotential evaluation, while asymmetrical for fuel cell performance and electrode overpotential measurement. The composite cathode was prepared similarly to the composite anode (Figure 3-18). The procedure follows ... 

Figure 4.1.52. (o), (b) Impedance spectra of cathode consisting of five layers of YSZ/LSM, with graded thickness and composition, (c) Circuit equivalent. The cathodes were prepared on both sides of a YSZ tape. The measurements were performed in air (Bonanos et al. [2002]). 

Murgia (2007) and Kakac et al. (2007)), which reflects the large sensitivity of this parameter to cathode composition and the preparation technique. 

The powders of Lao sSro 2peo 6Nio.403 and La9S3Si4 5Fei 5O26 were used for cathode composite materials preparation [55-56]. Their mixture was ultrasonically dispersed in water with addition of polyethylene glycol (2 w.%) as surfactant. The perovskite/apatite mass ratio was 1/1. The water emulsion obtained was filtered and perovskite/apatite mixture thus prepared was dried, pressed into pallets and sintered at 900,1100 and 1200°C. 

Yun, N.Ha, H.-W., Jeong, K H., Park, H.-Y. Kim, K. Synthesis and electrochemicai properties of olivine-type LiFeP04/C composite cathode material prepared from a poly[vinyl alcohol)-containing precursor. J. Power Sources, 160,1361 (2006). 

Fluorine cannot be prepared directly by chemical methods. It is prepared in the laboratory and on an industrial scale by electrolysis. Two methods are employed (a) using fused potassium hydrogen-fluoride, KHFj, ill a cell heated electrically to 520-570 K or (b) using fused electrolyte, of composition KF HF = 1 2, in a cell at 340-370 K which can be electrically or steam heated. Moissan, who first isolated fluorine in 1886, used a method very similar to (b) and it is this process which is commonly used in the laboratory and on an industrial scale today. There have been many cell designs but the cell is usually made from steel, or a copper-nickel alloy ( Monel metal). Steel or copper cathodes and specially made amorphous carbon anodes (to minimise attack by fluorine) are used. Hydrogen is formed at the cathode and fluorine at the anode, and the hydrogen fluoride content of the fused electrolyte is maintained by passing in... 

The reaction mixture is filtered. The soHds containing K MnO are leached, filtered, and the filtrate composition adjusted for electrolysis. The soHds are gangue. The Cams Chemical Co. electrolyzes a solution containing 120—150 g/L KOH and 50—60 g/L K MnO. The cells are bipolar (68). The anode side is monel and the cathode mild steel. The cathode consists of small protmsions from the bipolar unit. The base of the cathode is coated with a corrosion-resistant plastic such that the ratio of active cathode area to anode area is about 1 to 140. Cells operate at 1.2—1.4 kA. Anode and cathode current densities are about 85—100 A/m and 13—15 kA/m, respectively. The small cathode areas and large anode areas are used to minimize the reduction of permanganate at the cathode (69). Potassium permanganate is continuously crystallized from cell Hquors. The caustic mother Hquors are evaporated and returned to the cell feed preparation system. 

Schutt reported that the coke breeze specification and conditions in which the mix is prepared are important factors in determining the optimum operation of the conductive cement mix, whilst further details on the coke breeze asphalt mix composition are given by AndersonConductive concrete mixes, with a polymer binder have also been developed as an anode system specifically for reinforced concrete cathodic protection systems . 

In this method " - the melt eontains boric oxide and the metal oxide in a suitable electrolyte, usually an alkali or alkaline-earth halide or fluoroborate. The cell is operated at 700-1000 C depending on electrolyte composition. To limit corrosion, the container serving as cathode is made of mild steel or of the metal whose boride is sought. The anode is graphite or Fe. Numerous borides are prepared in this way, e.g., alkaline-earth and rare-earth hexaborides " and transition-metal borides, e.g, TiBj NijB, NiB and TaB... 

Takahashi et al. [220] first reported the formation of Bi-Te alloy films with varying chemical composition by means of cathodic electrodeposition from aqueous nitric acid solutions (pH 1.0-0.7) containing Bi(N03)3 and Te02. The electrodeposition took place on Ti sheets at room temperature under diffusion-limited conditions for both components. In a subsequent work [221], it was noted that the use of the Bi-EDTA complex in the electrolyte would improve the results, since Bi " is easily converted into the hydrolysis product, Bi(OH)3, a hydrous polymer, thus impairing the reproducibility of electrodeposition. The as-produced films were found to consist of mixtures of Te and several Bi-Te alloy compounds, such as Bi2Tc3, Bi2+xTe3 x, Bi Tee, and BiTe. Preparation of both n- and p-type Bi2Te3 was reported in this and related works [222]. 

Non-uniformity of composition sometimes can be exploited to advantage, e.g., in observing work function changes at a series of compositions, a sliding cathode photo tube (41), Fig- 4, was used. A curved substrate, either cylindrical or spherical, can also be used in preparing specimens with a broad range of concentrations (42) ... 

SEM images indicate that both graphite samples have very similar morphologies. Negative electrode laminates with active materials of SL-20 and SLC-1015 were then prepared using similar compositions. These laminates were then used to prepare negative electrodes that were inserted into Li-ion cells having similar cathodes and electrolyte materials. 

Figure 3.5 [36], For the 02 reduction reaction on freshly prepared LSM electrodes, the initial polarization losses are very high and decrease significantly with the cathodic polarization/current passage (see Figure 3.5b). Consistent with the polarization potential, the impedance responses at open circuit decrease rapidly with the application of the cathodic current passage. For example, the initial electrode polarization resistance, RE, is 6.2 Qcm2 and after cathodic current treatment for 15 min RK is reduced to 0.7 Qcm2 see Figure 3.5 (a). The reduction in the electrode polarization resistance is substantial. The analysis of the impedance responses as a function of the cathodic current passage indicates that the effect of the cathodic polarization is primarily on the reduction in the low-frequency impedance [10]. Such activation effect of cathodic polarization/current on the electrochemical activity of the cathodes was also reported on LSM/YSZ composite electrodes [56-58], Nevertheless, the magnitude of the activation effect on the composite electrodes is relatively small.

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