Copper hydrogen overvoltage

Pressure at elevated pressures, the value of the hydrogen overvoltage changes only very slightly but at lower pressures, it increases sharply on certain metals, as for example in the case of copper, nickel, and mercury cathodes. 

In nonaqueous, aprotic media, the hydrogen overvoltage does not play any role. Commonly used cathode materials are lead, aluminum, copper, titanium, steel, and carbon of all kinds. 

Lead has been much used as a cathode material ever since the beginning of organic electrochemistry it has a high hydrogen overvoltage and is easy to work mechanically. The purity of the material is important in some, but not in all, cases, and different procedures involving successively anodic and cathodic treatments have been recommended in order to obtain a pure, reproducible surfaces. Sometimes a lead cathode becomes deactivated during electrolysis, and a continuous addition of Pb to the catholyte may prohibit such a deactivation [123]. It has been observed that the chemistry of freshly deposited lead and copper is markedly different from that of bulk metal [124]. 

Schematically shown in Fig. 3 is the experimental set-up for preparation of graded foam stmctures. First, copper was used as the cathode in most of the experiments. Low hydrogen overvoltage of copper is beneficial to the energetic hydrogen evolution reaction in the course of copper deposition. The horizontal placement of copper substrate in the electrolyte bath ensures that the bubbles will move upward vertically upon formation on the surface. The anode is usually the same metal as that to be coated on the cathode. Platinum is sometimes used as the anode, especially... 

The reaction rate of sulfites with oxygen at low temperature is slow, so a catalyst is usually added, the best being cobalt, manganese, and copper salts. Cobalt gives the greatest increase in reaction rate. Copper should not be added to water that contacts steel or aluminum because it lowers the hydrogen overvoltage and increases the corrosion rate. 

Figure 21-6 shows the possibility of reducing the overvoltage of cathodic hydrogen evolution. One can also reduce restrictions in the O2 reduction hy using copper in lead alloys. Such alloying elements can be very effective because they... 

The most important factor in electrolytic reduction (electroreduction) is the nature of the metal used as a cathode. Metals of low overvoltage - platinum (0.005-0.09 V), palladium, nickel and iron - give generally similar results of reduction as does catalytic hydrogenation [727]. Cathodes made of metals of high overvoltage such as copper (0.23 V), cadmium (0.48 V), lead (0.64 V), zinc (0.70 V) or mercury (0.78 V) produce similar results to those of dissolving metal reductions. 

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