Cathode-limited cells

Sulfur dioxide is soluble in the electrolyte. Sulfur is soluble up to about 1 mol dm 3, but it precipitates in the cathode pores near the end of discharge. Lithium chloride is essentially insoluble and precipitates on the surfaces of the pores of the carbon cathode, forming an insulating layer which terminates the operation of cathode-limited cells [37],... 

An experimental investigation of explosion hazards in lithium-sulfinyl chloride cells on forced discharge showed cathode limited cells are safe, but anode limited cells may explode without warning signs [1]. Extended reversal at -40°C caused explosion on warming to ambient temperature, owing to thermal runaway caused by accelerated corrosion of lithium [2], The violent explosion of a large prismatic cell of a battery is described [3], Another study of explosion mechanisms in lithium/thionyl chloride batteries is reported [4]... 

In rechargeable nickel/zinc and sil-ver/zinc batteries this problem is partly compensated for by provision of a massive zinc reserve. The cells are cathode-limited and the amount of anode material exceeds the theoretically required mass by a factor between two and three. 

PEMFC)/direct methanol fuel cell (DMFC) cathode limit the available sites for reduction of molecular oxygen. Alternatively, at the anode of a PEMFC or DMFC, the oxidation of water is necessary to produce hydroxyl or oxygen species that participate in oxidation of strongly bound carbon monoxide species. Taylor and co-workers [Taylor et ah, 2007b] have recently reported on a systematic study that examined the potential dependence of water redox reactions over a series of different metal electrode surfaces. For comparison purposes, we will start with a brief discussion of electronic structure studies of water activity with consideration of UHV model systems. 

Irreversible Capacity. Because an SEI and surface film form on both the anode and cathode, a certain amount of electrolyte is permanently consumed. As has been shown in section 6, this irreversible process of SEI or surface layer formation is accompanied by the quantitative loss of lithium ions, which are immobilized in the form of insoluble salts such as Li20 or lithium alkyl carbonate. Since most lithium ion cells are built as cathode-limited in order to avoid the occurrence of lithium metal deposition on a carbonaceous anode at the end of charging, this consumption of the limited lithium ion source during the initial cycles results in permanent capacity loss of the cell. Eventually the cell energy density as well as the corresponding cost is compromised because of the irreversible capacities during the initial cycles. 

Table 11 shows some representative results from the cathodic reduction of some aromatic hydrocarbons. These include cases with Ei j2 near the cathodic limit or in the discharge region of the SSE (benzene, toluene) and cases with Ex j2 at considerably more positive potential (naphthalene, anthracene again we must anticipate the discussion of reactivity and refer to Table 21). Reactions nos. 1, 2, 6, and 7 immediately demonstrate one difficulty with such studies in that the catholyte of a divided cell becomes strongly basic as electrolysis progresses. In sufficiently basic medium, the initial product, a 1,4-dihydro derivative (cf. the Birch reduction Birch and Subba Rao, 1972), will rearrange to a conjugated system which, in contrast to the 1,4-dihydro derivative, is further reducible to the tetrahydro product (nos. 1 and 6). In a non-divided cell the acid production at the anode balances the base production and thus only a little rearrangement occurs. It is therefore not a trivial problem to find out if the tetrahydro product is formed from the conjugated dihydro product, formed directly or by rearrangement [eqn (78)].

This technique is limited to detection of the evolved gases from a PEC experiment. After illumination, the electrode should be analyzed for signs of corrosion and the electrolyte should be separately analyzed to evaluate the presence of any corrosion products. For the separate detection of gases from the anode and cathode, the cell should ideally be divided into two compartments using a separator such as a fine pore glass frit or ion exchange membrane (Fig. 9.2b) to prevent product crossover which can be a major limitation in single compartment cells. 

Limitation on caustic addition brine acidification maintenance of high cathode CE cell renewal Selection of salt better potash refining use of demineralized water in decomposers and ion-exchange regeneration Selection of salt chemical treatment ion exchange... 

The lithium chloride (LiCl) and sulfur (S) that form precipitate and build up at the cathode. The cell capacity can be limited by these products if the cathode becomes blocked. Additionally, sulfur dioxide (SO2) gas forms as a reaction product. 

The tubular cell used in the SOFC CHP-100 is a cathode-supported cell then, the main effect of diffusion is mainly addressed to the cathode layer. In terms of physieal measurable parameters, the cathode limiting current density can be evaluated in the form ... 

Either the anodic or cathodic half-cell reaction can become mass transport limited and restrict the rate of corrosion at co,r- The presence of diffusion controlled corrosion processes does not invalid the EIS method, but does require extra precaution and a modification to the circuit model of Fig. 4. In this case, the finite diffusional impedance is added in series with the usual charge transfer parallel resistance shown in Fig. 4. The transfer function for the frequency dependent finite diffusional impedance, Z fco), has been described [43] ... 

Rismani-Yazdi H, Carver SM, Christy AD, Tuovinen IH. Cathodic limitations in microbial fuel cells an overview. J Power Sources 2008 180 683-694. 

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