Electrochemical preparation of cuprous oxide powder: Part I. Basic electrochemistry

The preferred process for the production of cuprous oxide powder is via the anodic dissolution of copper in alkaline solution of sodium chloride. The principal reactions are as follows: $$\begin{gathered} Cu + nCl^ - = CuCl_n^{1 - n} (n = 2, 3) \hfill \\ 2H_2 O + 2e = H_2 \uparrow + 2OH^ - \hfill \\ 2CuCl_n^{1 - n} + 2OH^ - = Cu_2 O \downarrow + 2nCl^ - + H_2 O \hfill \\ \end{gathered} $$ In the present investigation the basic electrode processes were studied systematically under a broad range of conditions using linear sweep voltammetry. Variables studied include the concentration of sodium chloride and sodium hydroxide (i.e., alkalinity), temperature of the solution, two categories of additives (an inhibitor for preventing the deposition of spongy metallic copper powder on the cathodes, and a chemical reducing agent for reducing the cupric ions to the cuprous state), and the effect of carbonate ions (resulting from the spontaneous absorption of carbon dioxide from the air by sodium hydroxide). Useful guidelines concerning the electrolysis conditions, additives, and the concentration limit of carbonate ions have been established. The proper operating conditions can be considered to be as follows: 80–85°C, NaCl 240–260 gl^?1, NaOH below 1 gl^?1. Conditions pertaining to the use of additives are the following: calcium gluconate 0–5 gl^?1, Na₂CrO₄ below 0.5 gl^?1, Na₂Cr₂O₇ below 0.25 gl^?1, NH₂OH·HCl below 2.5 gl^?1, N₂H₄·H₂O below 2.5 gl^?1, sucrose 0–5 gl^?1. Special attention must be given to eliminate or reduce the presence of carbonate ions in the electrolyte below 0.25 gl^?1 Na₂CO₃.