Electrodes Electrolysis, alkaline water

Rosalbino F., Maccio D., Angelini E., Saccone A., Delfino S., Electrocatalytic properties of Fe-R (R = rare earth metal) crystalline alloys as hydrogen electrodes in alkaline water electrolysis, ]. Alloys Compd., 403(1-2), 275-282,2005. 

Hall DE (1981) Electrodes for alkaline water electrolysis. J Electrochem Soc 128 740... 

Wendt H., Hofmann H., Cermet diaphragms and integrated electrode-diaphragm units for advanced alkaline water electrolysis, Int. J. Hydrogen Energ., 10(6), 375-381,1985. 

Fig. 13 Current-voltage diagram showingthe meaning of activation overpotential for the electrolysis of water using platinum electrodes in alkaline solution. (Reprinted with permission from Ref. 8, Copyright 1998 by Wiley-VCH).

Key to meeting the market requirements is reducing the cost of electrolysis. Stuart s patented alkaline water electrolysis cell technology is designed to achieve the cost targets demanded by transportation fuels. The Double Electrode Plate... 

The electrolysis of water to generate hydrogen or oxygen is practised in certain situations where the cost of electricity is not a prime consideration. Large-scale plants have been built in Brazil, Canada, Egypt and Norway, which are countries that have surplus hydroelectric capacity. Generally, alkaline electrolyzers are employed and the electrode reactions are as follows ... 

The model was first verified for the case of a bipolar stack with fourteen Ni electrodes. " The electrochemical reaction used for the determination of current bypass was the electrolysis of water in alkaline solutions. Good agreement between experimental and estimated current bypass was observed, especially at high current densities. The model was adapted successfully for solid electrolyte cells of bipolar configuration, as discussed below in Section IV.2.i. 

Steam electrolysis splits water in the form of steam into hydrogen and oxygen by use of electricity and thus can be used as a method to produce hydrogen. Unlike other types of electrolysis, e.g., alkaline water electrolysis and polymer electrolyte water electrolysis, the steam electrolysis operates typically at 700-1,000 °C since the electrolysis uses solid electrolyte that works at the high temperatures. Such high operation temperature leads to fast kinetics for the electrode reactions, so that precious metals are not necessary for the electrocatalysis. 

The electrolysis of water at noble metal electrodes under carefully controlled conditions can be used for coulometric purposes. Provided appropriate temperature and pressure corrections are made, the volume of electrolysis products collected, i.e., hydrogen and oxygen gas, can be directly related to the number of coulombs passed in the electrolysis. Lehfeldt (25) recommended a sodium sulphate or dichromate electrolyte for best results. Kalnitskii (26), however, preferred to carry out the electrolysis at nickel electrodes in strongly alkaline media. 

Electrolysis cell. This is shown in Fig. VI, 31, 1 and is almost self-explanatory. The cylindrical cell of Pyrex glass (6" long by 2 " diameter) is cooled by immersion in a cooling bath. The electrodes consist of two platinum plates (4 cm. X 2-5 cm. X 0-3 mm.), which are placed about 2 mm. apart. The temperature of the electrolyte is maintained at 30-35° by means of the internal cooling coil and also by immersion of the cell in ice-water. A current of 1 5-2 0 amperes is passed until the electrolyte becomes slightly alkaline, which normally takes about 20-50 per cent, longer than the calculated time on the basis of the current and the amounts of acid employed. It is advantageous to reverse the direction of the current occasionally. 

Nidola A., Water electrolysis in alkaline solutions. New electrode materials, Int. ]. Hydrogen Energ., 9(5), 367-375,1984. 

The main reason for avoiding water as a solvent is the fact that the electrolysis of aqueous solutions of alkali and alkaline-earth metal salts commences at 1.7-2.0 volts (depending on the electrode material) and results in the evolution of O2 and H2. If the cell itself has a higher voltage, internal electrolysis can, but not always does occur, accompanied by the evolution of H2 and O2 and by self-discharge (117). However, this fact does not preclude attempts to create moist primary batteries with Li, Na or Ca, if the activity of H2O is kept sufficiently low. 

Fuel cells operate in a manner reverse to that of electrolysis, discussed in Chapter 2, combining fuel to make electricity. The basic design consists of two electrodes separated by an electrolyte. The oldest type of fuel cell is the alkaline fuel cell where an alkaline electrolyte like potassium hydroxide is used. The hydrogen enters through the anode compartment and oxygen through the cathode compartment. The hydrogen is ionized by the catalytic activity of the anode material and electrons are released into the external circuit. The protons react with the hydroxyl ions in the electrolyte to form water. The reaction can be written as ... 

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