Green hydrogen is a strong candidate to replace fossil fuels because it only generates only water and oxygen during combustion. Water electrolysis is a method for producing green hydrogen, but it has not been widely used because of its high operating cost. Various methods have been attempted to overcome this limitation and to reduce the energy required for water electrolysis.

In this study, a hybrid electrochemical system with three electrolyte chambers is constructed using an anion-exchange membrane (AEM), a cation-exchange membrane (CEM), and a buffer electrolyte between the AEM and the CEM. For simultaneous operation of desalination and water electrolysis, the hydrogen evolution reaction was performed under strongly acidic conditions, while the oxygen evolution reaction was performed under highly alkaline conditions.

In this system, the theoretical voltage required for water electrolysis was decreased from 1.229 V to 0.401 V based on the reaction potential changes depending on pH conditions. In addition, since ions are consumed in the electrode reactions, the movement of ions is essential to achieve charge equilibrium, which causes deionization in the buffer electrolyte. As a result, water electrolysis and desalination occurred simultaneously. The voltage for water electrolysis is lower than that of conventional water electrolysis systems.