Nickel voltage drop

Ferrous iron in the anolyte is oxidized to Fe " by dissolved chlorine. Since the solubility product of ferric hydroxide is very small ( 10 ), iron deposits on the membrane surface before it can penetrate the membrane. Iron, therefore, does not affect the selectivity of the membrane but may increase the voltage drop by reducing the effective area. Nickel has similar effects. Iron is generally less harmful because of very low solubility. However, it was reported [109] that in the presence of iron contamination, the current efficiency of Asahi Chemical cells with Aciplex membranes decreased by 2%. The cell voltage, on the other hand, was unaffected over 50 months of operation. The source of the iron was potassium ferrocyanide, an anticaking agent in the evaporated salt used as the raw material. 

The simplest action for a lesser voltage drop seems to be reducing of the electrode distance. However, this needs additional precautions. First of all, an improved precision of the electrolyzer components is indispensable, otherwise membrane crushing is to be expected. Furthermore, the necessity of hydrophilic membrane surfaces was discussed in section Technical Structure of Membranes for Qilor-Alkali Electrolysis. The ultimate possibility of minor electrode distance is zero gap, i.e., both electrodes are in contact with the membrane. Actual constmctions of this principle use an elastic element of fine, interwoven nickel wire for current feeding on the cathode side which presses the cathode (fine mesh) and the membrane onto the anode (e.g., [11]). 

Figure 2.22 shows the discharge characteristics at the 0.2, 1, and 3 C rate. The high-rate discharge characteristics of a nickel-MH battery compare unfavorably with those of a nickel-cadmium battery, because the specific surface area of the MH electrode is smaller than that of the cadmium electrode. Since the battery voltage drops dramatically if the discharge current exceeds 3 C, it is better to use a... 

Due to the cell voltage drop as a result of the decreasing fuel concentration towards the exhaust side of the stack, only a certain percentage of the available fuel can be electrochemically converted to electricity and heat. An overall utilisation of 85-90% is considered a practical maximum. At higher fuel utilisations, nickel may oxidise locally. A catalytic burner is used to burn the remaining fuel from the anode side with the surplus air from the cathode side. 

The solubility product of NiS was determined by linear voltage sweep voltammetry using a mercuric sulphide coated electrode (hanging mercury drop). The peak potential for the exchange reaction between the mercuric sulphide coated mercury electrode and Ni ions of a nickel perchlorate solution,... 

The Ni-Fe batteries range in size from 5 Ah to over 1,200 Ah. The cell open circuit voltage of the Ni-Fe cell is 1.4 which drops quickly to 1.2 V during discharge. Tubular or pocket plate COTistructiOTis are used. Active materials of high purity are contained inside the perforated nickel-plated steel tubes or rectangular pockets. The active materials are irrm for the negative electrode and nickel oxide for the cathode and a KOH electrolyte. 

The industrial preparation of hydrogen by the electrolysis of water on nickel electrodes requires a voltage of more than 1.50 V (1.23 V + 0.210 V + 0.060 V) since it is necessary to add the RI drop (due to the internal resistance of the electrolyte). However, at very high current densities, the polarization is much higher, and higher temperatures are used to reduce the excess power... 

If for instance an electronic memory bank with a continuous power consumption of 7 pA must be protected for at least 3 months, a battery with a capacity of 2200 hours x 7 pA is necessary. As the voltage is not allowed to drop below 1.2 V during operation, two primary button cells or two nickel/cadmium cells must be prescribed. A lithium cell would also do the job. 

Figure 31.10 indicates the capacity delivered by the nickel-zinc battery as a function of discharge rate and temperature. As the discharge current is increased, the battery output voltage decreases due to impedance and polarization losses. The data show that the eapacity is nearly independent of discharge rate, up to the 6C rate, but that the eapacity is somewhat dependent on temperature. The discharge capacity drops about 12% when the temperature decreases from 40°C to 0°C. 

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