Selective electrosynthesis of chlorine disinfectants from seawater

As one of the most widely used disinfectants, active chlorine is synthesized predominantly through electrolysis of saturated sodium chloride solutions, an industrial process known as the chlor-alkali process, with high energy consumption. Seawater is an abundant source of chloride and thus an ideal alternative electrolyte. However, substantial challenges are to be addressed, notably the competing oxygen evolution reaction and progressive anode passivation due to the presence of rich cations in seawater. Here, we show durable and efficient active chlorine electrosynthesis directly from natural seawater with intrinsic turnover frequency and mass activity two orders of magnitude higher than the state of the art. The essential chemistry is an Fe-doped Ti4O7 anode that strengthens the electrophilicity of lattice oxygen to allow for site-selective chloride activation at remarkably lowered kinetic overpotentials relative to the oxygen evolution reaction, while also impeding the precipitation of alkaline earth metal cations on the Ti4O7 surface. A seawater splitting device with an integrated commercial silicon photovoltaic cell delivers an impressive active chlorine production rate of 3.15 mg min−1 for effective simulated ballast water disinfection. This work suggests the possibility to substantially improve the sustainability of the chlor-alkali process without compromising the synthetic performance for the mass production of disinfectants.