Cell voltage nickel hydrogen

A clear advantage of alkaline electrolysers is the use of nickel-based electrodes, thus avoiding the use of precious metals. Catalytic research is aimed at the development of more active anodes and cathodes, primarily the development of high surface area, stable structures. Nickel-cobalt spinel electrodes for oxygen evolution and high surface area nickel and nickel cobalt electrodes for hydrogen evolution have been shown at the laboratory scale to lead to a decrease in electrolyzer cell voltage [47]. More active electrodes can lead to more compact electrolysers with lower overall systems cost. 

Potassium manganate obtained above is oxidized to the permanganate either by electrolysis or by chemical oxidation. Electrolytic oxidation is more common. Electrolytic cells have cathodes made of iron rods and nickel-plated anodes. Potassium manganate melt is extracted with water prior to its electrolysis and then electrolyzed at a cell voltage of 2.3V and current of about 1,400 amp. Permanganate is produced at the anode and water is reduced to gaseous hydrogen and hydroxyl ions at the cathode ... 

Figure 25 shows the evolution of cell voltage with time of Raney-nickel anodes that are deliberately operated at too high current densities so that the effectively applied overpotential was above the threshhold for nickel oxidation, which amounts to +80 mV vs the reversible hydrogen electrode. Evidently at a current density of 400 mA/cm2 and at 80°C the oxidation of Raney nickel proceeds within hours and at 300 mA/cm2 still within a week. 

Tokuyama Soda Company developed NiS and Ni-Sn alloy coated cathodes [194-197]. The hydrogen overvoltage of the electroplated Ni-Sn alloy cathode, with a nickel content of 40-80wt%, in a mixed solution of NaOH and NaCl at 90°C, was about 100 mV. The Ni-Sn cathodes were used in retrofit-type membrane cells and filter press-type electrolyzers, both operating at 4kAm and 80°C. The cell voltages were constant for over 8 years. 

The thermodynamic parameters are identical to those of the nickel/hydrogen battery, and the nominal cell voltage is also 1.3 V. This has the very important... 

In battery systems based on aqueous electrolyte, water decomposition, which occurs above a cell voltage of 1.23 V, is such an unavoidable secondary reaction. But under certain conditions the resulting water loss can be avoided, and the system is used as a sealed one, as achieved with sealed nickel/cadmium, nickel/hydrogen, and nickel/metal hydride batteries. In lead-acid batteries corrosion is an additional unwanted secondary reaction with the consequence that lead-acid batteries cannot be made virtually sealed, but must have a valve, and a certain water loss cannot be prevented. 

A low-cost nickel-hydrogen system proposed by Eagle Picher is based on the multiple cell per single battery pressure vessel concept. Additional system cost reduction is proposed through use of standardized components, ease of manufacture and an inherent design versatility able to meet various voltage and capacity requirements with only minor modifications. 

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