Solid anode materials

For water, organic and water-organic metal salts mixtures the dependence of integral and spectral intensities of coherent and non-coherent scattered radiation on the atomic number (Z), density, oscillator layer thickness, chemical composition, and the conditions of the registering of analytical signals (voltage and tube current, tube anode material, crystal-analyzer) was investigated. The dependence obtained was compared to that for the solid probes (metals, alloys, pressed powder probes). 

This reaction is of great technological interest in the area of solid oxide fuel cells (SOFC) since it is catalyzed by the Ni surface of the Ni-stabilized Zr02 cermet used as the anode material in power-producing SOFC units.60,61 The ability of SOFC units to reform methane "internally", i.e. in the anode compartment, permits the direct use of methane or natural gas as the fuel, without a separate external reformer, and thus constitutes a significant advantage of SOFC in relation to low temperature fuel cells. 

In 1968 DairOlio et al. published the first report of analogous electrosyntheses in other systems. They had observed the formation of brittle, filmlike pyrrole black on a Pt-electrode during the anodic oxidation of pyrrole in dilute sulphuric acid. Conductivity measurements carried out on the isolated solid state materials gave a value of 8 Scm . In addition, a strong ESR signal was evidence of a high number of unpaired spins. Earlier, in 1961, H. Lund had reported — in a virtually unobtainable publication — that PPy can be produced by electrochemical polymerization. 

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 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. 

An overview about more than 10 years of R D activities on solid electrolyte interphase (SEI) film forming electrolyte additives and solvents at Graz University of Technology is presented. The different requirements on the electrolyte and on the SEI formation process in the presence of various anode materials (metallic lithium, graphitic carbons, and lithium storage metals/alloys are particularly highlighted. 

Holze, R. and Wu, Y. P., Novel composite anode materials for lithium ion batteries with low sensitivity towards humidity, J. Solid State Electrochem. (2003) 8 66-72. 

There has been considerable interest in Ce02 as a component of solid oxide fuel cells, especially as an anode material, and also for use in oxygen separation membranes. The material shows a wide nonstoichiometry range, with oxygen vacancies as the... 

Summary of Previous Studies on Potential Sulfur-Tolerant Anode Materials for Solid Oxide Fuel Cells... 

Zhu WZ and Deevi SC. A review on the status of anode materials for solid oxide fuel cells. Mater Sci Eng 2003 A362 228-239. 

Jiang SP and Chan SH. A review on anode materials development in solid oxide fuel cells. J Mater Sci 2004 39 4405 1439. 

Gong M, Liu X, Trembly J, and Johnson C. Sulfur-tolerant anode materials for solid oxide fuel cell application. J Power Sources 2007 168 289-298. 

Yates C and Winnick J. Anode materials for a hydrogen sulfide solid oxide fuel cell. J Electrochem Soc 1999 146 2841-2844. 

Zha S, Cheng Z, and Liu M. A sulfur-tolerant anode materials for SOFCs GdjTij 4Mo06O7. Electrochem Solid-State Lett 2005 8 A406-A408. 

Huang Y-H, Dass RI, Xing Z-L, and Goodenough JB. Double perovskites as anode materials for solid oxide fuel cells. Science 2006 312 254—256. 

Lu XC and Zhu JH. Ni-Fe + SDC composite as anode material for intermediate temperature solid oxide fuel cell. J. Power Sources 2007 165 678-684. 

As a result, the acid strength of the proton is approximately equivalent to that of sulfuric acid in nonaqueous media. In view of the excellent miscibility of this anion with organic nonpolar materials, Armand et al. proposed using its lithium salt (later nicknamed lithium imide , or Lilm) in solid polymer electrolytes, based mainly on oligomeric or macro-molecular ethers. In no time, researchers adopted its use in liquid electrolytes as well, and initial results with the carbonaceous anode materials seemed promising. The commercialization of this new salt by 3M Corporation in the early 1990s sparked considerable hope that it might replace the poorly... 

Figure 9. Temperature programmed oxidation (TPO) data showing CO2 evolution m/e = 44) of thermally deposited carbon from a Cu-Ce02-YSZ SOFC anode material after exposure to n-butane for 30 min (solid line) and a graphite powder sample (dashed line). (Reprinted with permission from ref 172. Copyright 2003 The Electrochemical Society, Inc.)...

Also, a new composite consisting of a mixture of zinc and hydrated ammonium zinc sulfate has been elaborated and studied [341] as anode material for all solid-state protonic cells. Zn-Mn02 cells with this composite have a relatively high specific capacity. 

Metalliding. Metalliding, a General Electric Company process (9), is a high temperature electrolytic technique in which an anode and a cathode are suspended in a molten fluoride salt bath. As a direct current is passed from the anode to the cathode, the anode material diffuses into the surface of the cathode, which produces a uniform, pore-free alloy rather than the typical plate usually associated with electrolytic processes. The process is called metalliding because it encompasses the interaction, mosdy in the solid state, of many metals and metalloids ranging from beryllium to uranium. It is operated at 500—1200°C in an inert atmosphere and a metal vessel the coulombic yields are usually quantitative, and processing times are short controlled... 

Consumption of the graphite is quite acceptable inert anode materials for these conditions are hard to find, but in any event involvement of C in reaction 17.20 reduces the electricity requirement of the energy-intensive electrolysis by nearly half. Other, less commonly used processes that involve lower temperature electrolysis of molten AICI3 (mp 183 °C, performed in a closed vessel to prevent sublimation) have been developed. In these, the aluminum is formed as a solid (mp 660 °C), and the anodes are not consumed. Of course, one has to convert AI2O3 to A1C13 first, and this is usually done using graphite (coke) anyway ... 

If the cations in solution are condensable as a solid, such as copper, they can plate out on the cathode of the cell. As the same time, perhaps some hydrogen is also produced at the cathode. The SO 4 can react with a copper anode material by taking it into solution to replace the lost copper ions. Thus the anode is a consumable electrode in the process. 

Another way to decrease the anodic overpotential is to intercalate a mixed conductor between the yttria stabilized zirconia electrolyte and the metallic anode. Such a combination enlarges the reaction area which theoretically lowers the anodic overpotential. Tedmon et al. [93] pointed out a significant decrease of polarization when ceria-based solid solutions like (Ce02)o.6 (LaO, 5)04 are used as anode materials for SOFCs. This effect is generally attributed to the mixed conductivity resulting from the partial reduction of Ce4+ to Ce3+ in the reducing fuel atmosphere. A similar behaviour was observed in water vapor electrolysis at high temperature when the surface zirconia electrolyte is doped with ceria [94, 95]. 

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