Electrode-deposition

Tellurium [13494-80-9] M 127.6, m 450 . Purified by zone refining and repeated sublimation to an impurity of less than 1 part in 10 (except for surface contamination by Te02). [Machol and Westrum J Am Chem Soc 80 2950 1958.] Tellurium is volatile at 500°/0.2mm. Also purified by electrode deposition [Mathers and Turner Trans Amer Electrochem Soc 54 293 1928]. 

Figure 1.5. Schematic representation of a metal electrode deposited on a 02 -conducting (left) and on a Na -conducting (right) solid electrolyte, showing the location of the metal-electrolyte double layer and of the effective double layer created at the metal/gas interface due to potential-controlled ion migration (backspillover).

J.K. Hong, I.-H. Oh, S.-A. Hong, and W.Y. Lee, Electrochemical Oxidation of Methanol over a Silver Electrode Deposited on Yttria-Stabilized Zirconia Electrolyte, /. Catal. 163, 95-105 (1996). 

Figure 4.6.Scanning electron micrographs of a Ag catalyst-electrode deposited on YSZ and used for NEMCA studies10 (a) Top view (b) Cross section of the Ag/YSZ interface. Reprinted with permission from Academic Press.

P. Tsiakaras, and C.G. Vayenas, Oxidative Coupling of CH4 on Ag catalyst-electrodes deposited on Zr02(8mol% Y203), /. Catal. 144, 333-347 (1993). 

P.D. Petrolekas, S. Brosda, and C.G. Vayenas, Electrochemical promotion ofPt catalyst-electrodes deposited on Na3Zr2Si2PO 2 during Ethylene Oxidation,/. Electrochem. Soc. 145(5), 1469-1477 (1998). 

D. Tsiplakides, S. Neophytides, O. Enea, M.M. Jaksic, and C.G. Vayenas, Non-faradaic Electrochemical Modification of Catalytic Activity (NEMCA) of Pt Black Electrodes Deposited on Nafion 117 Solid Polymer Electrolyte, /. Electrochem. Soc. 144(6), 2072-2088 (1997). 

Consider the solid electrolyte cell shown in Figure 5.20. For simplicity we consider only a working (W) and reference (R) electrode deposited on a solid electrolyte, such as YSZ or p"-Al203. The two electrodes are made of the same metal or of two different metals, M and M. The partial pressures of 02 on the two sides of the cell are p02 and po2 Oxygen may chemisorb on the metal surfaces so that the workfunctions w and R(p 02). 

As already shown on Figures 5.8 and 5.11, Eqs. (5.18) and (5.19) have been obtained experimentally with polycrystalline Pt, Ag and Au catalyst electrodes deposited on YSZ and (3"-Al203. 

Figure 5.26. Effect of catalyst potential on the oxygen desorption activation energy, Ed, calculated from the modified Redhead analysis for Pt, Ag and Au electrodes deposited on YSZ.44,46 Reprinted from ref. 44 with permission from the Institute for Ionics.

Figure 5.30 exemplifies such a behaviour of a Pd catalyst electrode deposited on YSZ and exposed to CH4/02 mixtures.54 The resistance R is associated with the ohmic resistance of the electrode while the semicircles labeled Q and Ci- are associated with the charge transfer reaction... 

Similar is the behaviour with Ag electrodes deposited on YSZ as shown in Figures 5.40 and 5.41.68 The oxygen ion backspillover mechanism of electrochemical promotion is confirmed quite conclusively. 

Significant observations regarding the origin of NEMCA have been also made using Ultra-violet Photoelectron Spectroscopy (UPS) with Pt and Ag electrodes deposited on YSZ. In this case the work function of the electrode can be determined from the cutoff energy of secondary electrons (Fig. 5.43).24,68 As shown in Fig. 5.8b the change in the work function of the gas-exposed Ag surface is very close to the imposed electrode potential change AUwr. 

The obvious question then arises as to whether the effective double layer exists before current or potential application. Both XPS and STM have shown that this is indeed the case due to thermal diffusion during electrode deposition at elevated temperatures. It is important to remember that most solid electrolytes, including YSZ and (3"-Al2C)3, are non-stoichiometric compounds. The non-stoichiometry, 8, is usually small (< 10 4)85 and temperature dependent, but nevertheless sufficiently large to provide enough ions to form an effective double-layer on both electrodes without any significant change in the solid electrolyte non-stoichiometry. This open-circuit effective double layer must, however, be relatively sparse in most circumstances. The effective double layer on the catalyst-electrode becomes dense only upon anodic potential application in the case of anionic conductors and cathodic potential application in the case of cationic conductors. 

In a broad sense similar effective double layers can be formed via gaseous adsorption or evaporation (e.g. Na evaporated on Pt electrodes deposited on fT-A Ch has been shown to behave similarly to electrochemi-cally supplied Na). In other cases, such as the effective double layer formed upon anodic polarization of Pt deposited on YSZ, the electrochemically created effective double layer appears to be unique and cannot be formed via gaseous oxygen adsorption at least under realistic (<300 bar) oxygen pressure conditions. 

The transition from case 1 (no ion spillover) to case 2 (ion spillover) is shown in Figure 7.11 for Pt and Ag electrodes deposited on YSZ. At low temperatures (no spillover) significant deviations from Equation (7.11) are observed. As temperature is increased these deviations vanish and Equation (7.11) is satisfied. 

Figure 8.36. Scanning electron micrographs of an Ag-25at%Pd alloy electrode deposited on YSZ, (a,c,e) sample 1 (b, d, f) sample 2.39...

The oxidation of H2 at room temperature on Pt black electrodes deposited on Nafion 117 was the first electrochemical promotion study utilizing a solid polymer electrolyte.35... 

An important question frequently raised in electrochemical promotion studies is the following How thick can a porous metal-electrode deposited on a solid electrolyte be in order to maintain the electrochemical promotion (NEMCA) effect The same type of analysis is applicable regarding the size of nanoparticle catalysts supported on commercial supports such as Zr02, Ti02, YSZ, Ce02 and doped Zr02 or Ti02. What is the maximum allowable size of supported metal catalyst nanoparticles in order for the above NEMCA-type metal-support interaction mechanism to be fully operative ... 

Butene Isomerization on Pd Fully Dispersed on C Electrodes Deposited on Nafion... 

Two types of continuous flow solid oxide cell reactors are typically used in electrochemical promotion experiments. The single chamber reactor depicted in Fig. B.l is made of a quartz tube closed at one end. The open end of the tube is mounted on a stainless steel cap, which has provisions for the introduction of reactants and removal of products as well as for the insertion of a thermocouple and connecting wires to the electrodes of the cell. A solid electrolyte disk, with three porous electrodes deposited on it, is appropriately clamped inside the reactor. Au wires are normally used to connect the catalyst-working electrode as well as the two Au auxiliary electrodes with the external circuit. These wires are mechanically pressed onto the corresponding electrodes, using an appropriate ceramic holder. A thermocouple, inserted in a closed-end quartz tube is used to measure the temperature of the solid electrolyte pellet. 

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],... 

In the case of electrocatalytic operation, a galvanostat was used to apply constant currents I between the catalyst and a counter electrode deposited at the outer walls of the YSZ tube. In this way, oxygen is supplied to the Ag-based catalyst at a rate I/2F mol 0/s, where F is Faraday s constant. In this case the catalyst acts as an electrocatalyst [9,12,14]. 

Interesting fundamental studies and analytical applications of RRDEs have been published by Bruckenstein and co-workers the attraction of collecting experiments with the RRDE lies more especially in the fact that metals with different oxidation states are becoming more accessible to analysis, e.g., Cu(II) and Cu(I)127, U(VI) and U(V), Fe(III) and Fe(H). Shielding experiments were carried out for Bi(III) and Bi(0)128. Special use of stripping voltammetry with collection at a glassy carbon RRDE for the determination of tin in the presence of lead was proposed by Kiekens et al.129 after cathodic electrode-deposition... 

The Li-Ion system was developed to eliminate problems of lithium metal deposition. On charge, lithium metal electrodes deposit moss-like or dendrite-like metallic lithium on the surface of the metal anode. Once such metallic lithium is deposited, the battery is vulnerable to internal shorting, which may cause dangerous thermal run away. The use of carbonaceous material as the anode active material can completely prevent such dangerous phenomenon. Carbon materials can intercalate lithium into their structure (up to LiCe). The intercalation reaction is very reversible and the intercalated carbons have a potential about 50mV from the lithium metal potential. As a result, no lithium metal is found in the Li-Ion cell. The electrochemical reactions at the surface insert the lithium atoms formed at the electrode surface directly into the carbon anode matrix (Li insertion). There is no lithium metal, only lithium ions in the cell (this is the reason why Li-Ion batteries are named). Therefore, carbonaceous material is the key material for Li-Ion batteries. Carbonaceous anode materials are the key to their ever-increasing capacity. No other proposed anode material has proven to perform as well. The carbon materials have demonstrated lower initial irreversible capacities, higher cycle-ability and faster mobility of Li in the solid phase. 

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