Cl – /ClO – process on SnO 2 ‐based electrodes in low‐concentrated NaCl solutions

Abstract Anode processes on SnO 2 ‐based electrodes in low‐concentrated NaCl solutions have been investigated. The current‐voltage curves for 25 tin oxide anodes doped with various amounts of platinum group metals in 0.5 M NaClO 4 and 0.5 M NaClO 4 + 0.5 M NaCl have been analyzed. The correlation criterion between the catalytic activity of the coating in relation to the reaction of synthesis of NaClO, NaClO 3 from low‐concentrated NaCl solutions, and the oxygen evolution overpotential was found. The formulated criterion is fully met by SnO 2 ‐coatings doped with both palladium (5‐15 at.%) and platinum (5‐10 at.%), which are the optimal electrocatalysts for the synthesis of sodium hypochlorite. In this case, their catalytic activity does not depend on the concentrations of dopant in the range, which allows to obtain anodes with reproducible properties by pyrolysis. The current efficiency of NaClO is 90‐95% and current efficiency of chlorate is less than 1% during the electrolysis of 0.15 M NaCl on Ti/SnO 2 ‐Pt‐Pd anodes at 40‐60 mA/cm 2 . Palladium exists in the form of PdO phase in the electrocatalytic coating Ti/SnO 2 ‐Pt‐Pd. The surface oxygen concentration in H 2 O ads and OH ads is comparable to the oxygen content of the phase oxides of tin and palladium in the coating containing 19.5 at.% Pd, indicating a high surface content of adsorbed water. Palladium oxides are the main centers of water adsorption, and their presence on the surface of the anodes contributes to the hydroxylation of the surface. Most likely, this property of palladium compounds provides its high electrocatalytic activity in the reaction of formation of hypochlorite, which involves labile oxygen‐containing particles low bonded to the surface.