Influence of the platinum surface state on the selectivity of the electrochemical synthesis of sodium hypochlorite

Abstract

AbstractBACKGROUNDThe synthesis of sodium hypochlorite solutions by electrolysis of low‐concentration and isotonic NaCl solutions using the most available dimensionally stable anodes from platinized titanium is promising from the point of view of the economics of the process. However, such synthesis is seriously complicated by the formation of toxic sodium chlorate impurity.RESULTSIt is shown that in low‐concentration NaCl solutions under anodic polarization, the platinum surface rapidly passes into an oxidized passive state with a NaClO current efficiency (CE) of less than 30% and CE of NaClO3 of more than 20%. Carrying out short‐term electrolysis on the reduced surface of platinum makes it possible to increase the CE of NaClO to almost 90% in the absence of chlorate accumulation. Carrying out electrolysis in the mode of periodic change of electrode polarity (current reverse) allows solving the problem of anode passivation and significantly increasing the purity of the resulting sodium hypochlorite solutions.CONCLUSIONElectrolysis of an isotonic 0.15 mol L−1 NaCl solution in the current reverse mode allows increasing CE(NaClO) from 21% to 40% and significantly decreasing CE(NaClO3) from 21% to 4%. Based on the results obtained, a membraneless electrolyzer can be constructed to produce disinfectant solutions ‘on the spot’ using a commercially available pharmaceutical isotonic solution of NaCl. © 2023 Society of Chemical Industry (SCI).