Anode materials composite

Sacrificial anode material Composition Typical anodic current density (A.m") Consumption rate (g-A-. yr ) Cost per unit surface area (US /m ) 1-mm-thick anode Notes... 

Bouzek K, Schmidt Ml, Wragg AA (1999) Influence of anode material composition on the stability of electrochemically prepared ferrate (VI) solutions. J Chem Technol Biotechnol 74 1188-1194... 

Cells operating at low (2,80,81) and high (79,82) temperatures were developed first, but discontinued because of corrosion and other problems. The first medium temperature cell had an electrolyte composition corresponding to KF 3HF, and operated at 65—75°C using a copper cathode and nickel anodes. A later cell operated at 75°C and used KF 2.2HF or KF 2HF as electrolyte (83,84), and nickel and graphite as anode materials. 

The anode material in SOF(7s is a cermet (rnetal/cerarnic composite material) of 30 to 40 percent nickel in zirconia, and the cathode is lanthanum rnanganite doped with calcium oxide or strontium oxide. Both of these materials are porous and mixed ionic/electronic conductors. The bipolar separator typically is doped lanthanum chromite, but a metal can be used in cells operating below 1073 K (1472°F). The bipolar plate materials are dense and electronically conductive. 

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). 

The quality control of galvanic anodes is reduced mainly to the analytical control of the chemical composition of the alloy, to the quality and coating of the support, to an adequate joint between support and anode material, as well as to restricting the weight and size of the anode. The standards in Refs. 6, 7, 22, 27, 31 refer to magnesium and zinc anodes. Corresponding specifications for aluminum anodes do not exist. In addition, the lowest values of the rest potentials are also given [16]. The analytical data represent the minimum requirements, which are usually exceeded. 

Finally it must be remembered with these anodes that Pb02 film, which acts to provide the current leakage, can be detached even when no current is flowing. With renewed anodic loading, the film has to be reformed, which leads to a corresponding consumption of anode material. The anodes should therefore be operated as continuously as possible with a basic load. An exhaustive treatment of the composition and behavior of lead alloy anodes can be found in Ref. 13. 

It follows from the above that, for an anode material to offer sacrificial protection, it must have an open-circuit potential that is more negative than that of the structure itself (the cathode). The extent of protection experienced by the cathode will depend on the potential it achieves. This is dependent on the electrochemical properties of the anode which in turn are governed by its composition and the environment to which it is exposed. 

Many more exotic compositions for anode materials are often encountered in the literature. It should be appreciated, however, that continual mention in texts of these materials in no way reflects their usage or acceptance commercially as viable sacrificial anodes. 

It is a valve metal and when made anodic in a chloride-containing solution it forms an anodic oxide film of TiOj (rutile form), that thickens with an increase in voltage up to 8-12 V, when localised film breakdown occurs with subsequent pitting. The TiOj film has a high electrical resistivity, and this coupled with the fact that breakdown can occur at the e.m.f. s produced by the transformer rectifiers used in cathodic protection makes it unsuitable for use as an anode material. Nevertheless, it forms a most valuable substrate for platinum, which may be applied to titanium in the form of a thin coating. The composite anode is characterised by the fact that the titanium exposed at discontinuities is protected by the anodically formed dielectric Ti02 film. Platinised titanium therefore provides an economical method of utilising the inertness and electronic conductivity of platinum on a relatively inexpensive, yet inert substrate. 

The physicochemical properties of carbon are highly dependent on its surface structure and chemical composition [66—68], The type and content of surface species, particle shape and size, pore-size distribution, BET surface area and pore-opening are of critical importance in the use of carbons as anode material. These properties have a major influence on (9IR, reversible capacity <2R, and the rate capability and safety of the battery. The surface chemical composition depends on the raw materials (carbon precursors), the production process, and the history of the carbon. Surface groups containing H, O, S, N, P, halogens, and other elements have been identified on carbon blacks [66, 67]. There is also ash on the surface of carbon and this typically contains Ca, Si, Fe, Al, and V. Ash and acidic oxides enhance the adsorption of the more polar compounds and electrolytes [66]. 

COMPOSITE ANODE MATERIALS FOR HIGH ENERGY DENSITY LITHIUM-ION BATTERIES... 

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. 

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. 

Yang S, Cui G, Pang S, Cao Q, Kolb U, Feng X, Amier J, Mullen K. Fabrication of cobalt and cobalt oxide/graphene composites Towards high-performance anode materials for lithium batteries, ChemSusChem 2010, 3, 236-239. 

Anode Materials General Requirements A major problem and thus a decisive factor for the choice of anode materials is corrosion, except when the dissolution of a metal is the desired reaction ( sacrificial anodes , see Sect. 2.4.1.2.4). The stability of anode materials is extremely dependent on the composition of the anolyte (e.g. pH value, aqueous or non-aqueous medium, temperature, presence of halogenides, etc.). 

The anode material in SOFCs is a cermet (metal/ceramic composite material) of 30 to 40 percent nickel in zirconia, and the cathode is... 

Endo et al. investigated the reductive decomposition of various electrolytes on graphite anode materials by electron spin resonance (ESR). In all of the electrolyte compositions investigated, which included LiC104, LiBF4, and LiPFe as salts and PC, DMC, and other esters or ethers as solvents, the solvent-related radical species, which were considered to be the intermediates of reductive decomposition, were detected only after prolonged cathodic electrolysis. With the aid of molecular orbital calculation, they found that the reduction of salt anion species is very difficult, as indicated by their positive reduction enthalpy and that of free solvent (A/4 — 1 kcal mol ). However, the coordination of lithium ions with these solvents dramatically reduces the corresponding reduction enthalpy (A/ —10 kcal mol ) and renders the reaction thermodynamically favored. In other words, if no kinetic factors were to be considered, the SEI formed on carbonaceous anodes... 

The extent of the irreversible capacity depends on both the anode material and the electrolyte composition. Empirical knowledge indicates that the PC presence, which is well-known for its tendency to cause the exfoliation of the graphene structures, is especially apt to induce such irreversible capacities. On the other hand, reformulation of the electrolyte may lead to significant reduction in the irreversible capacity for given electrode materials. 

As a demanding reaction, it is very sensitive to the structural and compositional details of the anode materials. For this reason, research on anodes for O2 evolution calls for close characterization of electrocatalysts, especially from the point of view of materials chemistry and physics. 

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. 

ZnO displays similar redox and alloying chemistry to the tin oxides on Li insertion [353]. Therefore, it may be an interesting network modifier for tin oxides. Also, ZnSnOs was proposed as a new anode material for lithium-ion batteries [354]. It was prepared as the amorphous product by pyrolysis of ZnSn(OH)6. The reversible capacity of the ZnSn03 electrode was found to be more than 0.8 Ah/g. Zhao and Cao [356] studied antimony-zinc alloy as a potential material for such batteries. Also, zinc-graphite composite was investigated [357] as a candidate for an electrode in lithium-ion batteries. Zinc parhcles were deposited mainly onto graphite surfaces. Also, zinc-polyaniline batteries were developed [358]. The authors examined the parameters that affect the life cycle of such batteries. They found that Zn passivahon is the main factor of the life cycle of zinc-polyaniline batteries. In recent times [359], zinc-poly(anihne-co-o-aminophenol) rechargeable battery was also studied. Other types of batteries based on zinc were of some interest [360]. 

Other common anode materials for thermal batteries are lithium alloys, such as Li/Al and Li/B, lithium metal in a porous nickel or iron matrix, magnesium and calcium. Alternative cathode constituents include CaCr04 and the oxides of copper, iron or vanadium. Other electrolytes used are binary KBr-LiBr mixtures, ternary LiF-LiCl-LiBr mixtures and, more generally, all lithium halide systems, which are used particularly to prevent electrolyte composition changes and freezing out at high rates when lithium-based anodes are employed. 

Presently, only a few materials are used as the anode, and metal Ni is conventionally used as the anode material. In order to ensure that the TEC of the electrolyte and anode agree, a cermet (a composite of Ni and YSZ) is used for the anode. With increasing YSZ ratio, the TEC of the anode becomes close to that of YSZ but the electric conductivity of the anode decreases. Usually, 40 60 molai% of YSZ is mixed with Ni. 

Anode materials are required to have a high electrocatalytic activity for the partial oxidation of the fuel in order to facilitate Reaction (1). Consequently, several anode materials have been tested including various compositions of Ni-cermets such as 70 wt.% Ni/30 wt.% YSZ (Ni + YSZ), 70 wt.% Ni/30 wt.% Sm0.2Ceo.8Ox (Ni + CSO), and 60 wt.% Ni/40 wt.% Gdo iCeo gOx (Ni + CGO). Because cathode materials exhibit a high electro-catalytic activity for the reduction of the oxygen in order to facilitate reaction (4), several cathode materials have also been tested, including various compositions of (La, Sr) (Co, Fe)C>3 (LSCF), and CSO-LSCF. 

Well-established anode materials are Ni cermets such as Ni/YSZ composites. The presence of the second phase increases the contact area and prevents the catalytically active Ni particles from aggregating. The use of the composite becomes problematic if hydrocarbons are to be directly converted Ni catalyzes cracking, and the resulting carbon deposition deactivates the fuel cells. Therefore either pure H2 has to be used or the fuel has to be externally reformed. A third way is internal conversion of CHV with H20 to synthesis gas. The necessary steam addition, however, reduces the overall efficiency. Another problem of Ni cermets, if they are to be used at lower temperatures, is a potential oxidation of the Ni. Alternatives are Cu/Ce02 cermets in which Cu essentially provides the electronic conductivity and Ce02 the catalytic activity. Note that an efficient current collecting property of the electrode presupposes a metal concentration above the percolation threshold. 

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