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The nature of the cathode material is an important factor in electrolytic reduction.  By using a material with a high hydrogen overvoltage, a higher cathode potential and, therefore, greater reducing energy may be obtained, without the liberation of gaseous hydrogen.¹  Tafel² showed that the reduction of substances like pyridine and compounds containing the keto group, reducible only with great difficulty, can be accomplished readily at cathodes of lead and mercury -- metals with high hydrogen overvoltages -- whereas little or no reduction takes place at a platinum cathode.  Frequently, reduction proceeds further and with a higher current efficiency at a mercury than at a lead cathode.  From the results of his experiments, Tafel concluded that "substances which are difficult to reduce can only be reduced in sulphuric acid solution, when such cathodes are employed as give a particularly high overvoltage."  In order to secure this high hydrogen overvoltage, it is essential that the metal of the cathode be free from impurities, as often even traces of foreign metals lower the overvoltage considerably. When lead cathodes are used in these reductions, they first must be treated electrolytically.³
     It has been suggested that the cathode potential in electrochemical reduction processes can be controlled by means of a specially designed circuit.⁴
     (b) Physical Condition of the Cathode. The physical condition of the cathode may exert an influence on electrochemical reduction.⁵  In the electrochemical reduction of benzoic acid at cathodes of 99.99+ per cent lead, Swann and Lucher obtained better yields of benzyl alcohol when the metal was extruded than when it was cast; and they found that after prolonged use the activity of the cathode decreased, owing to diminution in the crystal size of the lead surface as well as to the formation lead sulphate.  These same investigators found the yield of benzyl alcohol at a cadmium cathode to be associated with the ability of the metal to undergo a macro etch of its surface, the yield being approximately proportional to the extent of etching which the surface underwent.

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Since a high current density not only raises the cathode potential but also decreases the concentration of the depolarizer in the vicinity of the cathode, electrolytic reduction is, in general, more rapid and complete the lower the current density.  That is, a large cathode surface should be employed.  Obviously, an increase in the concentration of the depolarizer will also contribute to more efficient reduction.  Effective stirring is likewise advantageous.

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(f) Applications of Electrochemical Reduction.  In the practical application of electrochemical reduction, it must be remembered that the products formed at the cathode are likely to be oxidized at the anode.  In order to prevent this from happening, the anode is frequently separated from the cathode by a diaphragm.⁵  The portions of electrolyte contained in the sections thus formed are termed the anolyte and catholyte, respectively.  The same end can sometimes be attained by employing a high anodic current density (ie., a small anode surface) or, in alkaline solutions, iron or nickel anodes -- metals with the smallest oxygen overvoltages.

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from Principles and Applications of Electrochemistry 4th Edition H. J. Creighton Vol. 1 1943


Also,

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In addition to the conductors themselves small quantities of salts and other compounds are sometimes added to promote reduction or oxidation (see section on factors influencing reduction and oxidation, pages 415-16 and 440).  Promoters of the reduction are:  salts of copper, titanium, tin, lead, vanadium, and molybdenum, arsenic and antimony oxides, and ketones.  Promotors of oxidation are oxidizing agents such as potassium ferricyanide, and ceric and manganic salts.

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Another factor which may influence the efficiency of a cathode is the orientation of the crystals in the cathode.  The yields of benzyl alcohol at extruded lead rod cathodes as received were decidedly higher that those at the same lead after it had been recast.⁵⁶  It is possible that some preferred orientation of the crystals had occurred when the lead recrystallized after extrusion.  The yields of benzyl alcohol compared favorably with those obtained at lead electroplated from a perchlorate bath....

....Surface Treatment.  Caffeine is easily reducible at the spongy surface of "prepared" (see page 418) and also at a roughened lead cathode when not reducible at a smooth surface.⁶³

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(page 418)
A lead cathode is "prepared" by a modification of the Tafel⁸⁰ method whether it is to be used in acid or in alkaline solution.  The cathode to be use is placed as before in a 20% solution of sulfuric acid surrounded by a sheet of lead.  The cathode is used as anode under the conditions described above except that the current is allowed to flow for 5 minutes.  A layer of chocolate brown lead oxide forms on the surface of the lead used as anode.  The polarity is reversed and the current again allowed to flow for 5 minutes.  The lead oxide is reduced to spongy metallic lead.  The cycle is repeated.  At the end of the second cycle a third is begun, but the cathode is left in the oxidized condition.  It is washed thoroughly with distilled water before being used in the reduction.

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from Technique of Organic Chemistry Vol. II, Catalytic, Photochemical, Electrolytic Reactions, 2nd edition, Interscience Publishers, Inc. New York, 1956