Positive electrodes performance, improvement

The nickel-cadmium battery was invented by Jungner in 1899. The battery used nickel hydroxide for the positive electrode, cadmium hydroxide for the negative electrode, and an alkaline solution for the electrolyte. Jungner s nickel-cadmium battery has undergone various forms of the development using improved materials and manufacturing processes to achieve a superior level of performance. 

However, it can undergo self-reductive dissolution (loss of active material) accompanied by oxygen evolution [349]. The active material of the positive electrode (in pocket plate cells) consists of nickel hydroxide mixed with small additions of cobalt and barium hydroxides to improve the capacity and charging/discharging performance and graphite to improve conductivity [348]. 

Among the transition metal oxides, mention should also be made of the vanadium oxides, the most studied as positive electrode materials being V2O5, V Oii, and LiV30g, which insert lithium in the potential domain of 3 V vs. Li/Li+. For the vanadium oxides, too, doping and suitable structure have been shown to improve their electrochemical performance, and recently a sol-gel process has yielded high-capacity (500-600 Ah kg ) materials delivering 500 Wh kg at 4 mA cm" [137]. 

Improved kinetics at the positive electrode. The electrochemical reduction of oxygen is also a complex process each molecule requires the transfer of four electrons for complete reduction. Surface intermediates are formed and these lower the kinetic performance of the electrode. Platinum-based electrocatalysts are necessary to allow the reaction to proceed at a useful rate. A more effective and cheaper alternative electrocatalyst is an ongoing research target, as is equally the case for positive electrodes in PEMFCs. 

One of the ways for the improvement of the positive electrode is to use a composite obtained by the impregnation of multiwall carbon nanotubes (MWNTs) by liquid sulfur. MWNTs with a high true surface area and high electron conductivity, on the one hand, promote retention of polysulfides in the positive electrode bulk (thus decreasing the shuttle transfer and self-discharge) and, on the other hand, enhance the electrode performance across its depth. 

Another possible approach for future studies might be hybridization of the method with other cell separation methods. One good potential might be hybridization of dielectrophoretic method and acoustophoretic method. Dielectrophoresis is chosen for hybridization since this method is extensively studied and its separation performance can be improved by keeping the distance between the cells and the electrode (s) consistently close. In that sense, the positioning of cell can be achieved by positioning the cells towards a pressure node. As an example. 

The positive electrode consists of Ni(OH)2 in alternate layers of nickel flake. High purity nickel metal powder or chip is dissolved in sulfuric acid. Hydrogen is used in making the negative iron active material. The acidity is adjusted to pH 3 or 4 to remove iron and other insoluble materials. Further conditioning to remove aU of the ferrous iron and copper may be needed. Cobalt sulfate is added at about the 1.5% level to improve the nickel performance. The resulting sulfate solution is heated and... 

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