Common-Ion Effect Triggered Highly Sustained Seawater Electrolysis with Additional NaCl Production.

Pengsong Li,Shiyuan Wang,Yang Li,Zhiyi Lu,Xingheng Zhang,Imran Ahmed Samo,Xiaoming Sun,Yun Kuang,Xijun Liu,Yiyun Du,Cheng Wang,Congtian Cheng,Zhaolei Wang,Yang Zhong,Wenwen Xu

doi:10.34133/2020/2872141

Abstract

Developing efficient seawater-electrolysis system for mass production of hydrogen is highly desirable due to the abundance of seawater. However, continuous electrolysis with seawater feeding boosts the concentration of sodium chloride in the electrolyzer, leading to severe electrode corrosion and chlorine evolution. Herein, the common-ion effect was utilized into the electrolyzer to depress the solubility of NaCl. Specifically, utilization of 6 M NaOH halved the solubility of NaCl in the electrolyte, affording efficient, durable, and sustained seawater electrolysis in NaCl-saturated electrolytes with triple production of H2, O2, and crystalline NaCl. Ternary NiCoFe phosphide was employed as a bifunctional anode and cathode in simulative and Ca/Mg-free seawater-electrolysis systems, which could stably work under 500 mA/cm2 for over 100 h. We attribute the high stability to the increased Na+ concentration, which reduces the concentration of dissolved Cl− in the electrolyte according to the common-ion effect, resulting in crystallization of NaCl, eliminated anode corrosion, and chlorine oxidation during continuous supplementation of Ca/Mg-free seawater to the electrolysis system.

Highlights

Hydrogen, with a high gravimetric energy density of 142 MJ/kg, is considered one of the most promising clean energy carriers [1,2,3]
The common-ion effect is demonstrated in Figure S2: when NaOH were added into the saturated NaCl solution (~5.3 M), the NaCl crystals precipitated from the solution due to the increased concentration of Na+
In order to highlight the importance of the “common-ion effect,” we conduct a control experiment by adding KOH in saturated NaCl

Summary

Introduction

With a high gravimetric energy density of 142 MJ/kg, is considered one of the most promising clean energy carriers [1,2,3]. Electrochemical water splitting is a promising and green pathway that converts the sustainablerenewable energy resources into H2 [4,5,6,7]. Seawater splitting [8,9,10] receives great attention due to the abundant resources (~97% of water in our planet) on earth and avoiding the competition to drinking water [11,12,13], as well as concentrating high-value elements to maximize the utilization of seawater. Contemporary works employed mimic seawater in alkaline electrolyte (e.g., 0.5 M NaCl +1 M KOH) as water source and reported attractive electrolysis performance [9, 10, 20]. Pure water instead of seawater is usually fed in long-term stability testing (>100 hours) for Research

Methods

Results

Conclusion