Cathodes water electrolyzers

Membrane water electrolyzers, platinum and platinum metal cathodes, 40 122 p-Menthane, 20 281... 

Water electrolyzer units typically consist of several cells or electrodes arranged in two basic configurations, tank type operated in unipolar configuration, or filter press type operated in bipolar configuration. Tbe most common configuration, see Fig. 2.1, is the unipolar tank type where each electrode has only one polarity and all the electrodes of the same polarity are connected in parallel. The anodes and cathodes are alternately connected, with the... 

C. Platinum and Platinum Metal Cathodes in Membrane Water Electrolyzers... 

Carbides were first proposed as anodes for H2 ionization in electrochemical power sources [422], The higher activity of WC with respect to W for H2 evolution was discovered about forty years ago [423], but the first practical proposals for the use of carbides as cathodes are found only recently under the influence of research aimed at the development of more efficient water electrolyzers [424]. More recently, aqueous suspensions of WC have been proposed to catalyze H2 formation in the presence of the reduced form of a redox relay that is continuously generated through a photochemical reaction [425]. 

Figure 5.1.6 Comparison of the energy efficiencies and current densities for C02 reduction to formic acid, syngas, and hydrocarbons (methane and ethylene) reported in the literature with those of water electrolyzers. Efficiencies of electrolyzers are total system efficiencies, while the CO2 conversion efficiencies only include cathode losses and neglect anode and system losses. Adapted from [17],...

The first water electrolyzers used the tank design and an alkaline electrolyte.20 These electrolyzers can be configured as unipolar (tank) or bipolar (filter press) designs. In the unipolar design (see Figure 1), electrodes, anodes, and cathodes are alternatively suspended in a tank. In this design, each cell is connected in parallel and the entire system operated at 1.9-2.5 Vac. 

This type of device has been contrasted489 with a series connection of a photovoltaic p-n junction solar cell and a water electrolyzer. Unlike the latter which is a majority carrier system (i.e., the n-side of the junction is the cathode and the p-side becomes the anode), in a photochemical diode, minority carriers (holes for the n-type and electrons for the p-type) are injected into the electrolyte. This distinction translates to certain advantages in terms of the overall energetics of the solar energy conversion system (see Ref. 489). 

Early work by Gerischer and Mehl (106) employed impedance analysis at Ag and Cu electrodes. However, these metals are not of major interest as H adsorption is weak, and these materials are not attractive as water electrolyzer cathodes. Bockris et al. (121) and Selvaratnam and Devanathan (122) employed the double-pulse method (see Section VI,B,1) for Ag and Ni, but the results did not seem to be very meaningful. 

Recently, much interest has centered on the electrocatalytic behavior of Ni-Mo alloyst (prepared electrolytically or by thermal reduction of oxide or molybdate mixtures) for cathodic H2 evolution in alkaline-water electrolyzers or as cathodes in electrolytic CI2 cells. The h.e.r. at these electrode materials exhibits remarkably low Tafel slopes, in the range 22-26 mV, at elevated temperatures, 363 K. This is one of the reasons for their excellent behavior as electrocatalysts for the h.e.r. However, the Tafel slopes exhibited by these materials depend on temperature in a most unusual way, decreasing with increasing temperature, as do some of the results at NP (Fig. 4). 

The problem of ohmic drops by diaphragms has been studied for a long time. A laboratory scale diaphragm-less water electrolyzer was developed for hydrogen production at large pressures of up to 140 kPa by electrolysis in an alkaline solution. Porous electrodes with a nickel catalyst and a copper cover layer serve as cathodes, whereas nickel sheets are used as anodes. Modular construction of the electrolyzer permits simple combination of its cells into larger units. Thus, up to 20 cells with diskshaped electrodes of 7 cm in diameter were connected in series and provided with electrolyte manifolds, automatic pressure, and electrolyte level control devices. The dimensions of the electrolyte manifolds were optimized based on the calculations of parasitic currents [50],... 

Another important factor which affects the current distribution is the void fraction within the electrolyte. It is obvious that the design variables involved to minimize the void fraction would be (1) electrode height, (2) liquid flow rate through the anode and cathode compartments, and (3) anode structure. Asahi Chemical operate at high pressures to compress the bubble volume and hence, the void fraction as practiced (see Ref. 14 for details) in some water electrolyzers. Recent studies109,110 on the effect of electrode structure on void fraction show that expanded mesh electrodes generally give low void fraction. 

Leakage currents can be short circuited [64] or biased by placing an opposite current via electrodes placed in the piping [40] or reacted at sacrificial electrodes located in the manifolds [65]. These concepts have been used in the manifolds of MBC electrolyzers of Chlorine Engineers and also in the design of the CME and BiTac cells. Corrosion of catalytic cathodes used in bipolar water electrolyzers during shutdowns is prevented by cathodic protection [9]. 

The reactor employed aluminum electrodes supplied by DC power. Chemical oxygen demand (COD), color, conductivity, pH and turbidity were monitored during the process. Aluminum dissolved at the anode, with water electrolyzed at the cathode to produce aluminum hydroxide and hydrogen gas. These reactions and hydroxide precipitation resulted in changes in solution pH during the process. Aluminum solubility was affected by solution pH, which was found to affect COD and color removal. 

Sodium tetraethylborate in water electrolyzed with Hg-cathode and Bi-anode with 0.120 Faraday at 3.5 amp./qdm. and 1.8 v. triethylbismuth. Y ... 

Proof of the formation of hydronium ions in solutions was provided many years ago by an elegant experiment (19) in which hydronium bromide was electrolyzed in sulfur dioxide to produce a mole of water per faraday at the cathode. Water is nearly insoluble in sulfur dioxide and hydrogen bromide is soluble, but not ionized in this medium. However, when both are present water goes into solution easily to give a highly conducting solution. We shall reserve the more complex question of the nature of the hydronium ion in aqueous acid for a later section on the quantitative measurement of the basicity of water. 

Cold fusion has been reported to result from electrolyzing heavy water using palladium [7440-05-3] Pd, cathodes (59,60). Experimental verification of the significant excess heat output and various nuclear products are stiU under active investigation (61,62) (see Eusion energy). 

That is, water is electrolyzed. The hydrogen gas produced at the cathode can be hazardous, especially because it is in the vicinity of an electrode that is also producing heat. For this reason, electrode chambers are usually open to the atmosphere so that gases can vent. 

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