Collector Material

In normal battery operation several electrochemical reactions occur on the nickel hydroxide electrode. These are the redox reactions of the active material, oxygen evolution, and in the case of nickel-hydrogen and nickel-metal hydride batteries, hydrogen oxidation. In addition there are parasitic reactions such as the corrosion of nickel current collector materials and the oxidation of organic materials from separators. The initial reaction in the corrosion process is the conversion of Ni to Ni(OH)2. 

The main criteria for the selection of the current collector material in a central sulfur cell or for the cell case material in a central sodium cell are corrosion resistance to sulfur and sodium polysulfides, good electrical conductivity, and low costs. This cost argument has led to coated materials which have been compared with nickel—chromium alloys (Inconel 600). 

In the next paper by Y. Illin et al., capabilities of Sn anodes are considered as a possible alternative to carbon. Thin films of Sn were deposited onto current collector in vacuum, and tested in the coin cells. Authors were able to obtain reversible alloying reaction, which stabilized at 100 mAh/g between cycle number 100 and 400. The stability of Sn and its characteristics upon cycling was seen to be a function of the current collector material. The best results were achieved with non-copper-based substrates. 

The NASA Genesis mission (see Box 4.3), launched in 2001, was designed to collect solar wind over a 2.5-year period. Special collector materials were designed to be free of contaminants so that clean measurements of the isotopic compositions of trapped solar wind... 

Because of the low operating temperature, PTFE can be used for the cell seals which simplifies cell assembly. The high operating voltage, however, leads to problems of corrosion and the only current collector material which has been found to show any corrosion resistance is tungsten. If sulphur is not added to the melt, a nickel current collector can be used, but omission of sulphur adversely affects the operation of the positive electrode. The problems encountered with the positive electrode were so severe that the development of this cell was discontinued. 

Compared with a conventional bipolar transistor, the tunnel collector efficiency is low and this means the collector base current gain, is modest for such transistors. This current is determined not just by base recombination as is usual in standard transistors but also by the fraction of carriers that evade the collection process. Another unusual feature is the form of the output admittance, which is determined by the upper band structure of the ferromagnetic collector material and the effective tunnel barrier width. It is therefore non-negligible and is predictably a function of Vce. 

Development of Refractory Metal Oxide Collector Materials and Their Thermionic Converter Performance... 

Accordingly, the collector materials produced by FGM technology can have a spatially dependent work function. In other words, FGM technology makes it possible to realize the new hybrid mode. 

Efforts to improve the ratio of effective to theoretical specific energy involve, in general (1) replacement, where possible, of inert grid, container, connector, and current collector materials by lightweight substances (2) increase of utilization of active materials by improved cell design and/or use of special additives (3) careful modeling and optimization of current collection and (4) use of bipolar electrodes. 

It appears that instead of a simple electrode a complicated one emerged, and a suitable (cheap and redox stable) current collector material has not yet been demonstrated. Nevertheless, ceria based anodes have important advantages over conventional Ni-based anodes, namely the ability to endure repetitive oxidation and reduction (redoxing) and the ability to avoid (or tolerate) carbon deposition from... 

Airborne may be collected in any of the forms discussed in Section 5.3.2. Samples may arrive with several forms in the same collector for separation at the laboratory, or the forms may already be separated at collection. Most commonly, tritiated water vapor is brought to the laboratory as a water sample. When collected on silica gel or molecular sieve, tritiated water vapor is removed by heating the collector material in a distillation flask above the boiling point of water. The vapor is transferred to a separate flask and condensed. A measured amount of the condensed water is analyzed for tritium in a liquid scintillation (LS) counter in terms of becquerel per gram water. If the collector is silica gel, the result must be corrected for dilution by a small amount of water originally in the silica gel (Rosson et al. 2000). In addition, a small isotope effect, mentioned in Section 4.8, results in distilling a greater fraction of H2O than HTO unless the entire sample is distilled. 

Finally, the stainless-steel bipolar plate consists of a separator and current collectors. The plate is exposed to the anodic environment on one side and the cathodic environment on the other. The low oxygen partial pressure on the anodic side of the bipolar plate prevents the formation of a protective oxide coating and, on the cathode side, the contact electrical resistance increases as an oxide scale builds up. Active research is focused on finding alloys for bipolar current-collector materials that function well in both anodic and cathodic environments, have a low cost and ohmic resistance, and have good corrosion resistance [15]. 

Conducting polymers constitute another category of promising pseudo-capacitive materials. The most common ones include polypyrrole (PPy), polyaniline (PANI), and poly-(3,4)-ethylenedioxythiophene (PEDOT). This group is of particular interest due to low cost and ease of synthesis. These compounds can be polymerized directly onto a collector material via EPD. Alternatively, the polymerization can be done within surfactant emulsions... 

In many cases, electrode materials or pastes are grown or deposited (e.g., spray coat, drop coat, spin coat, application of electrode paste) directly onto collector material to provide a good molecular contact created by drying and annealing of the electrode [125]. To further minimize resistance, a highly conductive coating that exhibits improved interfacial contact between components can be applied. Without low resistance connections, the electrode performance of a good material can otherwise be lost. 

Nyquist plots recorded using two-electrode symmetric supercapacitor in 0.5 M Na2S04 aqueous solution. The electrode layers with active surface area of 4.0 cm are composed of BP2000 carbon particles as active material and stainless steel as current collector material. AC frequency range = 0.3Hz to 122KHz. (Source Zhang, L. and J. Zhang. 2011. NRC unpublished data. 

Solid-state redox mediators or hole conductor materials would make it possible to construct completely solid-state DSSCs that will probably have considerable added commercial value. One of the main difficulties in substituting liquid electrolytes is the need for an interpenetration of the sensitised metal oxide by the electrolyte, in order to have efficient contact between the sensitiser cation (the hole) and the mediator. Additionally, prospective solid hole collectors should have the following properties the valence band of the hole collector material must be located above the bottom of the sensitiser dye ground state it must be transparent throughout the visible spectrum, where the dye absorbs fight and the deposition of the solid material should be done without degrading the monolayer of sensitiser dye adsorbed on Ti02. 

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