APPLICATION OF A GAS DIFFUSION CATHODE IN ELECTROCHEMICAL SYNTHESIS OF SODIUM HYPOCHLORITE

Abstract

During the electrochemical synthesis of sodium hypochlorite, it was proposed to change the nature of the cathode process to eliminate the cathode reduction of hypochlorite ions. Changes in the nature of the cathode process from hydrogen evolution to oxygen reduction are created by supplying oxygen to the cathode-electrolyte interface. Changing the nature of the cathode process will significantly reduce the difference in electrode potentials. By controlling the rate of oxygen supply, the supply of ClO– to the cathode surface is inhibited. The process of electrochemical oxygen reduction was investigated using a gas diffusion cathode in the electrolysis of aqueous solutions of sodium chloride. Graphite mark PG-50 was used as a porous cathode. The graphite electrode was activated by treatment in oxidizing agents to create a layer of active carbon compounds on its surface. Nickel oxides were deposited by thermal decomposition of nickel nitrate. Gas diffusion mode was created by supplying air to the back surface of the porous cathode. The effect of the electrode material on the cathode polarization dependences in an aqueous solution of NaCl on porous graffiti and graffiti activated by nickel without air supply, with moderate air supply and air supply with excess, is investigated. Graphite, activated by nickel oxides, showed great catalytic activity in the oxygen reduction reaction. The equilibrium potentials of a graphite electrode without coating and with an activating coating were investigated in an aqueous solution 3 mol×dm-3 NaCl. The obtained polarization dependences on the materials under study prove that the air supply to the gas diffusion electrode changes the course of the current-voltage dependence. A significant shift of the equilibrium potential in the negative direction indicates the influence of adsorption processes in the formation of a double electric layer at the electrode-electrolyte interface. Replacing the nature of the cathode process of hydrogen evolution by oxygen reduction allows increasing the current efficiency up to 52 % and NaCl concentration up to 27 g·dm–3. The nature of the flow of the cathode oxygen reduction process when changing the mode of air supply is analyzed. The balance electrochemical synthesis of sodium hypochlorite for 10 hours proved the effectiveness of the proposed technical solution.