Electrolyte Engineering Applying Concentrated Chloride Ions with Mixed Buffer Solutions for a Versatile High-Productivity Water-Splitting System
Hiroki Komiya, Keisuke Obata, Melody Wada, Takeshi Nishimoto, Kazuhiro Takanabe
Abstract
High Resolution Image Download MS PowerPoint Slide Seawater electrolysis is an attractive way for green hydrogen production; however, it faces challenges in efficiency loss because of the overpotentials in the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), high concentration overpotential, and high ohmic potential ( iR ) drop. Here, our electrolyte engineering approach led to the introduction of a highly conductive Cl – -containing borate/carbonate mixed buffer electrolyte. At a borate/carbonate molar ratio of 1.0, this electrolyte has a new apparent p K a (p K a,app ) of pH 9.8. While a typical water electrolysis system removes Cl – to avoid competitive Cl – oxidation, we intentionally utilized concentrated Cl – to improve conductivity, reaching around 50 S m –1 at 353 K, making the value competitive with 30 wt % KOH (∼130 S m –1 ). In this mixed buffer electrolyte with Cl –, the performances for HER using RuNiO x H y /Ni felt and for OER using CoFeO x H y /Ti felt were, respectively, optimized by electrolyte engineering, tuning the concentration of cations and operating pH. The two electrodes, highly conductive electrolytes, and newly adopted polyethersulfone separator led to a zero-gap cell that worked stably at 2.00 V and 500 mA cm –2 with 106 mV iR loss and unity gas faradaic efficiency for 80 h under non-extreme pH conditions. This study provides a new design of electrolyte engineering for seawater splitting.