Photoelectrochemical production of disinfectants from seawater

Active chlorine, including HClO and ClO−, is one of the most extensively used disinfectants. However, it is mainly produced through energy-consuming three-step chlor-alkali electrolysis of saturated brine using Cl2 gases as intermediates. Here we report a photoelectrochemical synthetic pathway from natural seawater using a chloride-mediated NbClOx/BiVO4 photoanode. The photoanode presents an onset potential of 0.6 V versus a reversible hydrogen electrode (VRHE) and over 500 h of stability in seawater under one sun illumination. The faradaic efficiency and selectivity of hypochlorite are close to 100% at 1.2–1.8 VRHE with a yield of 119.9 ± 9 μmol cm−2 h−1 at 1.72 VRHE. Meanwhile, value-added products of Mg(OH)2 and CaCO3 are obtained on the cathode, accompanied by hydrogen production. Further analyses show that the present process reduces electricity consumption by 77.16% and CO2 emissions by 75.31%. Our findings suggest a strategy with combined safety, efficiency and economic feasibility for direct synthesis of active chlorine from seawater. Active chlorine is the most widely used water disinfectant, but its production has environmental consequences. This work shows a photoelectrochemical synthetic route using only solar energy and seawater.