Anodes Based on Conversion Reaction

The conversion or redox, reaction involves the formation and decompositiOTi of Li20 according to the so-called conversion-displacement reaction [480-483]  

We have already seen in the previous sections that graphene sheets have been widely used as an ideal matrix for anchoring a number of active anode materials to form unique nanocomposites. Such has been also the case with CoO. Until recently, however, these cobalt oxide/graphene nanocomposites have a relatively low 

The ensemble of porous structures and one-dimensional shape has also proved to be efficient for NiO-anodes, just as in the other anodes. Mesoporous NiO nanotubes using filter paper as the template presented a reversible capacity of 600 mAh g after 100 cycles at current rate 200 mA g [516]. Hierarchically porous NiO microtubes synthesized by a high temperature calcination of Ni(dmg 2 (dmg = dimethyl-glyoxime) microtubes obtained by a simple precipitation method of PEG 2000 (poly(ethylene glycol)) to hollow the nanostructure delivered a capacity 640 mAh g after 200 cycles at 1 A g . The investigation of the rate capabiUty revealed reversible capacities of 810,780,720,630, and 520 mAh g at 50, 200, 500, 1000, and 2000 mA g . More importantly, a discharge capacity of 800 mAh g can be recovered, while the current density back to 50 mA g . It indicates the high stability of NiO microtubes [517]. 

Coating NiO has not been so successful. To avoid the barrier that a uniform coat of NiO with a metal could rise for the lithium transport, a composite NiO/Co-P has been synthesized with NiO particles 200 nm in size, and 30 nm thick granular plating particles of Co-P [518]. This anode delivered the discharge and charge capacities 560 and 540 mAh g, respectively, after 50 cycles at current density 100 mA g . At the higher current densities of 200, 500, and 1000 mA g, the reversible capacities were 560,480, and 270 mAh g, respectively. Among NiO/Ni composites [519-521], the best results over 50 cycles have been found on self-supported nickel-coated NiO arrays prepared by chemical bath depositiOTi of NiO flake arrays 

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On the other hand, although tin electrodeposition on metallic substrate deserved significant interest for developing batteries, it is worth to note that the anodic oxidation of a tin foil can produce porous electrodes [78]. Similarly, electrodeposited transition metals can be oxidized to form porous oxide films on flat metal substrate [38]. These porous transition metal oxides—although they are based on conversion reactions—exhibit a considerable pseudocapacitance. 

For anode materials based on conversion reaction, there are three main disadvantages, such as low columbic efficiency, high average charging voltage, and high polarization. 

Anodes Based on Both Alloying and Conversion Reaction... 

Again, points on the curve were the measured acrolein production rates, and the line is the predicted production rate based on the current and the stoichiometry according to eq 9. At higher conversions, we observed significant amounts of CO2 and water, sufficient to explain the difference between the acrolein production and the current. It should be noted that others have also observed the electrochemical production of acrolein in a membrane reactor with molybdena in the anode. The selective oxidation of propylene to acrolein with the Cu—molybdena— YSZ anode can only be explained if molybdena is undergoing a redox reaction, presumably being oxidized by the electrolyte and reduced by the fuel. By inference, ceria is also likely acting as a catalyst, but for total oxidation. 

The interaction of these two processes can be described by a simple isothermal model, which is based on balances of mass and charge. The model describes the extent of the reforming and oxidation reactions along the anode channel. The essential simulation results can easily be displayed in a conversion diagram which is a phase diagram of the two dynamic state variables, namely the extents of two reactions. 

The reactive semiconductor-electrolyte interface makes stability a major issue in photoelectrochemical solar energy conversion devices, and aspects of thermodynamic and kinetic stability are briefly reviewed here. Thermodynamic stability considerations are based on so-called decomposition levels [56, 57] that are determined by combining the decomposition reaction with the redox reaction of the reversible hydrogen reference electrode. The anodic and cathodic decomposition reactions of a compound semiconductor MX can be written for aqueous solutions as... 

Based on a co-flow configuration, the effect of various parameters on cell performance has been studied systematically. The study covers the effect of (a) air flow rate, (b) anode thickness, (c) steam to carbon ratio, (d) specific area available for surface reactions, and (e) extend of pre-reforming on cell efficiency and power density. Though the model predicts many variables such as conversion, selectivity, temperature and species distribution, overpotential losses and polarization resistances, they are not discussed in detail here. In all cases calculations are carried for adiabatic as well as isothermal operation, fii calculations modeling adiabatic operation the outer interconnect walls are assumed to be adiabatic. All calculations modeling isothermal operation are carried out for a constant temperature of 800°C. Furthermore, in all cases the cell is assumed to operate at a constant voltage of 0.7 V. 

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