Active chlorine electrosynthesis from dilute chloride solutions in a flow cell equipped with a Ti|Ti-Ru-Ir-oxides anode

Abstract

This investigation reports the electrosynthesis of active chlorine from diluted chloride solutions using an undivided filter-press lab scale electrolyzer equipped with Ti|Ti-Ru-Ir-oxides anode and stainless-steel cathode. The interest in studying dilute chloride solutions to yield active chlorine (mixture of Cl2, HClO and ClO−) is because such chloride amounts are typically found in wastewater samples. The influence of the initial chloride concentration (20 ≤ CCl− ≤ 50 mM), anodic applied potential (1.5 ≤ E ≤ 1.8 V vs. SHE), and mean linear flow velocity (2.5 ≤ u ≤ 12.5 cm s−1) on the active chlorine accumulation was systematically examined. The initial electrolyte also contains 50 mM Na2SO4 at pH 3; such pH favors the formation of HClO (with the highest oxidizing power). The best electrolysis regarding the active chlorine accumulation (202 mg L−1) gave 34.4 % current efficiency, and 0.009 kWh (g active chlorine)−1 in 50 mM Cl− solution using E = 1.6 V vs. SHE, and u = 10 cm s−1. The modest current efficiency is due to the concurrent active chlorine formation with the oxygen evolution reaction (OER) at the Ti|Ti-Ru-Ir-oxides anode. The pH increases from 3 to 7.6 over the electrolysis (t = 240 min) due to the hydrogen evolution reaction (HER) occurring at the cathode; at these pHs, a mix of HClO and ClO− species are produced. The well-engineered electrolyzer used herein to form active chlorine species envisages its future use in electrochemical advanced oxidation processes to incinerate persistent organic pollutants.