Dimensionally stable electrodes

Miscellaneous. Iridium dioxide, like RUO2, is useful as an electrode material for dimensionally stable anodes (DSA) (189). SoHd-state pH sensors employing Ir02 electrode material are considered promising for measuring pH of geochemical fluids in nuclear waste repository sites (190). Thin films (qv) ofIr02 ate stable electrochromic materials (191). 

Dimethyl sulphoxide has also been oxidized electrochemically, using either a platinum anode or a dimensionally stable anode containing iridium and selenium in 1 M sulphuric acid solution158. The former electrode requires a potential close to that required for oxygen evolution whilst the latter needed a potential 0.5 volts lower. Thus the dimension-... 

Appreciable interest was stirred by the sucessful use of nonmetallic catalysts such as oxides and organic metal complexes in electrochemical reactions. From 1968 on, work on the development of electrocatalysts on the basis of the mixed oxides of titanium and ruthenium led to the fabrication of active, low-wear electrodes for anodic chlorine evolution which under the designation dimensionally stable anodes (DSA) became a workhorse of the chlorine industry. 

Of considerable interest was the demonstration that metalloporphyrins and the like can be used as nonmetallic catalysts in electrochemical reactions, nourishing hopes that in the future, expensive platinum catalysts could be replaced. Starting in 1968, dimensionally stable electrodes with a catalyst prepared from the mixed oxides of titanium and ruthenium found widespread use in the chlorine industry. 

Ru02 is an important electrode material for industrial anodic processes. Special attention is deserved by the so-called dimensionally stable anodes (DSA) invented by H. B. Beer in 1968. These are formed by a layer of a microcrystalline mixture of Ti02 and Ru02 (crystallite size less thn 0.1 jum) on a titanium support (Fig. 5.26). This material is suitable as anode for chlorine and oxygen evolution at high current densities. For industrial chlorine production, it replaced the previously used graphite anodes. These... 

Fig. 5.26 Beer-De Nora dimensionally stable electrode with a Ru02-Ti02 layer...

Technical electrodes usually consist of a mixture of Ru02 and TiC>2 plus a few additives. They are called dimensionally stable anodes because they do not corrode during the process, which was a problem with older materials. These two substances have the same rutile structure with similar lattice constants, but RuC>2 shows metallic conductivity, while pure TiCU is an insulator. The reaction mechanism on these electrodes has not yet been established the experimental results are not compatible with either of the two mechanisms discussed above [4]. 

DSA-02 oxide-coated Ti anode (DSA = Dimensionally Stable Anode) is placed, thus creating a large cathode volume. The effluent solution flows perpendicularly through the electrodes with a typical flow rate of 0.5 dm3 s-1. The flowthrough metal electrodes have an active area approximately 15 times their geometric area. The cell allows air sparging to increase the mass-transfer. The current efficiency is about 40% when the inlet concentration of the metal ions is 150 to 1500 ppm and the concentration at the out-let is about 50 ppm. The cell is currently used for the treatment of recirculated wash-waters from acid copper, copper cyanide, zinc cyanide, zinc chloride, cadmium sulphate, cadmium cyanide and precious metal plating and washwaters from electroless copper deposition. Since the foam metal electrodes are relatively expensive the electrodes... 

The laboratory unit was based on a ElectroCell MP cell with an elec-trode/membrane area of 0.01 m2. A DSA (Dimensionally Stable Anode) anode served as oxygen electrode, Ni as cathode. Anion exchange membranes = Neosepta ACM (Tokuyama Soda) AMH cation ex-change membranes = Nafion 324 Nation 902. 

Laboratory apparatus represents an important application sector. Platinum crucibles, dishes, boats and electrodes for electrogravimetry have long been basic items in chemical laboratories. Today the more dimensionally stable alloys Pt97-Ir3, Pt95-Au5, Pt99.7-Ir0.3 are mainly used. Platinum components are essential in fluorine chemistry. 

II. Electrocatalytically Activated Dimensionally Stable Chlorine-Evolving Electrodes... 

Materials for the Construction of Cells and Electrodes. Materials used for the construction of cells should be usable over a wide temperature range, dimensionally stable, impervious to aqueous and organic solvents and reagents, durable, and easy to machine or fabricate. Another highly desirable property is for the material to be transparent so that the electrodes and the solution can be observed. 

Dimensionally stable anodes represent, from the commercial point of view, one of the more important inventions in the history of industrial electrochemistry. Even so, carbon electrodes were an entrenched and stable part of the mindset of the chlorine production community. deNora s sales technique was at first to offer use of the new electrodes at zero cost, only asking for half the dollar gains obtained by a company s use of the new electrodes. This technique created a market for the new electrodes, so that it could soon be replaced with a more normal sales technique. 

Dimensionally stable alloys (examples 11-13 in Table 8). In these composite alloys, the active alloy (usually a binary one) is encapsulated in another alloy that forms a rigid matrix. For instance, in example 13, an active LiCd alloy is hosted in a much less active, but rigid Li-Sn matrix. Hence, stable electrodes of relatively low volume change upon cycling can be composed, provided that the potential is kept strictly within limits in which only the active alloy reacts electrochemically, while the stable alloy remains inert. 

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