Electrolyte Engineering Applying Concentrated Chloride Ions with Mixed Buffer Solutions for a Versatile High-Productivity Water-Splitting System

Developing highly active electrocatalystsand conductiveelectrolytes can boost the overall water-splitting efficiency in thepresence of chloride ions. Seawater electrolysisis an attractive way for green hydrogen production;however, it faces challenges in efficiency loss because of the overpotentialsin the oxygen evolution reaction (OER) and the hydrogen evolutionreaction (HER), high concentration overpotential, and high ohmic potential(iR) drop. Here, our electrolyte engineering approachled to the introduction of a highly conductive Cl--containing borate/carbonate mixed buffer electrolyte. At a borate/carbonatemolar ratio of 1.0, this electrolyte has a new apparent pK (a) (pK (a,app)) of pH 9.8. Whilea typical water electrolysis system removes Cl- toavoid competitive Cl- oxidation, we intentionallyutilized concentrated Cl- to improve conductivity,reaching around 50 S m(-1) at 353 K, making the valuecompetitive with 30 wt % KOH (& SIM;130 S m(-1)).In this mixed buffer electrolyte with Cl-, the performancesfor HER using RuNiO (x) H (y) /Ni felt and for OER using CoFeO (x) H (y) /Ti felt were, respectively, optimizedby electrolyte engineering, tuning the concentration of cations andoperating pH. The two electrodes, highly conductive electrolytes,and newly adopted polyethersulfone separator led to a zero-gap cellthat worked stably at 2.00 V and 500 mA cm(-2) with106 mV iR loss and unity gas faradaic efficiencyfor 80 h under non-extreme pH conditions. This study provides a newdesign of electrolyte engineering for seawater splitting.