Copper oxide electrodes

For ethanol and 1-propanol the oxidation at copper oxide electrodes gives similar yields as at the nickel hydroxide electrode However, for 1-butanol the yields are already less satisfactory (copper oxide 77%, 25 °C silver oxide 26%, 25 Copper and silver anodes tend to corrode in alkaline medium, which, however, may be limited by the use of a divided cell... 

Oxidation of peptides and amino acids at copper oxide electrodes is achieved at very high pH (typically in 0.1 M hydroxide) and potentials in the range of +0.40 to +0.60 V versus Ag/AgCl [112-114], In this potential range, a copper electrode is covered with a Cu(Il) oxide film (CuO) containing hydroxyl radicals that can described as CuO( OH) [113-115]. Amino acids that have been oxidized include Ala, Arg, Asn, Asp, Cys, Gin, Gly, His, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr and Val [112,107], and it has been suggested that oxidation occurs according to [113] ... 

General Electric patented a high temperature pH sensor where a yittria stabilized zirconia tube provides the selective migration of hydrogen ions to an inner copper oxide electrode. The pH sensor has been shown to agree within 0.5 pH of calculated values at 285 C between 3 and 9 pH with uncertainty as whether the discrepancies were due to the calculation or the measurement. There is no alkalinity error. However, the speed of response of the membrane degrades with time [Ref. 4.11 and 4.12]. The expected life expectancy of a few months and a reported drift of 0.1 pH per day needs investigation. 

There are many methods of fabricating the electrodes for these cell systems. The eadiest commercially successhil developments used nickel hydroxide [12054-48-7] Ni(OH)2, positive electrodes. These electrodes are commonly called nickel electrodes, disregarding the actual chemical composition. Alkaline cells using the copper oxide—2inc couple preceeded nickel batteries but the CuO system never functioned well as a secondary battery. It was, however, commercially available for many years as a primary battery (see BatterieS-PRIMARY cells). 

To exploit the energy produced in this reaction, the half reactions are separated. The oxidation reaction is carried out at a zinc electrode (Zn Zir + 2 electrons) and the reduction reaction is carried out at a copper electrode (Cu"" + 2 electrons Cu metal). Electrons flow through a metal wire from the oxidizing electrode (anode) to the reducing electrode (cathode), creating electric current that can be harnessed, for example, to light a tungsten bulb. 

One more example demonstrates how to use standard reduction potentials to determine the standard potential of a cell. Let s say you wanted to construct a cell using silver and zinc. This cell resembles the Daniell cell of the previous example except that a silver electrode is substituted for the copper electrode and a silver nitrate solution is used in place of copper sulfate. From Table 14.2, it is determined that when silver and copper interact silver is reduced and copper oxidized. The two relevant reactions are... 

The lower amines have been oxidized in similar yields to nitriles at silver oxide and copper oxide anodes Activation of the electrode by deposition of a nickel hydroxide oxide layer is less essential than with alcohols due to the higher reactivity... 

Copper electrodes have been used to determine amino acids and carbohydrates [10]. Metal oxide electrodes (including thin-film semiconductors) show some promise, but nothing of substance has yet been published with regard to LCEC. Pulsed amperometric detection (PAD) takes advantage of metal oxides formed in situ. This approach is discussed later. 

This detection system is coupled with anion-exchange chromatography (48,49), which has the same alkaline pH requirements. The sensitivity of PAD is considerably higher than that yielded using the refractometric detector, with detection limit being of the order of 10 pmol (29). On the other hand, its response also depends heavily on the nature of the carbohydrate. Finally, other alternatives described in the literature include the use of nickel-based or copper-based electrodes and catalytic oxidation (50). 

Secondly, if the first oxidation wave cannot be attributed to metallic copper oxidation, only one oxidisable compound is left, namely Cu(I). Indications for this can be found in the fact that in Cu(I)-containing styrene solutions, the limiting-current of this first oxidation wave is much higher than for Cu(II)-containing solutions. As a matter of fact, the first oxidation wave is expected to be absent in Cu(II) solutions. Apparently, the presence of this wave has to be attributed to the fact that some Cu(I) is present in the vicinity of the electrode surface. When the position of the current-potential curves in Fig. 12.2 reflects the standard potentials of the... 

The galvanic cell shown in Figure 1 is known as the Daniell cell and was used as an early source of energy. It consists of a zinc (Zn) electrode in contact with an aqueous zinc sulfate solution and a copper (Cu) electrode in contact with an aqueous copper sulfate solution. When the external switch is closed, an atom of zinc on the zinc electrode is oxidized to zinc ion, liberating two electrons. 

Photochemical reduction of C02 was also achieved in the presence of the p-type semiconductor (copper oxide) or silicon carbide electrodes [97]. Irradiation of this system generates methanol and methane as the main products in the case of CuO electrode whereas hydrogen (with efficiency about 80%), methanol (16%), methane, and carbon monoxide in the case of SiC electrode. Also Ti02/CuO systems appeared relatively efficient (up to 19.2% quantum yield) in photocatalytic C02 to CH3OH reduction [98]. 

The standard electrode potentials are far more anodic than that of one-electron transfer process, -0.284 V (SHE) and the visible-light photocatalytic activity of platinum-loaded tungsten(VI) oxide could be interpreted by enhanced multiple-electron transfer process by deposited platimun (45), since it is well known that platinum and the other noble metals catalyze such multiple-electron transfer processes. Similar phenomena, cocatalyst promoted visible-light photocatalytic activity, have been reported with palladium 46) and copper oxide (47). Thus, change of reaction process seems beneficial to realize visible-light photocatalytic activity. 

The adsorption of CN on a polycrystalline copper electrode has been studied experimentally by Lee et al. [116], Since copper oxidizes more readily than gold and silver, the results depend strongly on the cyanide concentration. At low cyanide concentration in solution (2x 10 M), a potential dependent band between 2084 and 2120cm was assigned to the linearly adsorbed CN ion (Fig. 33, p. 172). 

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