Electrochemical synthesis of NaClO solutions on Ti/Pt electrodes in current reverse mode

Abstract

BACKGROUND

The synthesis of sodium hypochlorite (NaClO) by classical electrolysis of NaCl solutions on a Ti/Pt anode is characterized by parallel formation of undesirable sodium chlorate (NaClO₃) impurities. Oxidation of hypochlorite to chlorate with high current efficiency (CE) is realized on the oxidized, passivated Pt surface. On a Pt surface reduced by cathodic polarization, NaClO synthesis can be realized with the CE close to 90% almost without chlorate accumulation. Long-term electrolysis leads to passivation of the Pt surface.

RESULTS

Electrolysis while periodically changing the polarity of the electrodes (current reverse mode) increases the time the Pt surface remains in the activated state. Carrying out electrolysis in this way makes it possible to increase CE(NaClO) 1.5–2.0-fold while simultaneously reducing CE(NaClO₃) (sodium chlorate) by ≤10-fold. This study additionally determined the optimal parameters of reverse electrolysis, examined the effect of changing polarity on the state of the Ti/Pt electrode surface and studied the kinetic patterns of active platinum coating dissolution.

CONCLUSION

The optimal conditions for electrolysis in current reverse mode are current densities of 5–10 mA cm⁻² with the period of polarity change close to 30 s. The result of such a process is an isotonic solution containing 500 mg L⁻¹ NaClO with an admixture of <10 mg L⁻¹ NaClO₃ and 0.1 mg L⁻¹ Pt in the form of soluble chloride complexes. The rate of Pt accumulation is determined by the frequency of polarity change. The resulting solutions have sufficiently high purity for use in medicine and aerosol air disinfection. © 2024 Society of Chemical Industry (SCI).