A clean and membrane-free chlor-alkali process with decoupled Cl2 and H2/NaOH production

Mengyan Hou,Zhaowei Guo,Yonggang Wang,Yongyao Xia,Xiaoli Dong,Long Chen

doi:10.1038/s41467-018-02877-x

Abstract

Existing chlor-alkali processes generally use asbestos, mercury or fluorine-containing ion-exchange membranes to separate the simultaneous chlorine production on the anode and hydrogen production on the cathode, and form sodium hydroxide in the electrolyte. Here, using the Na+ de-intercalation/intercalation of a Na0.44MnO2 electrode as a redox mediator, we decouple the chlor-alkali process into two independent steps: a H2 production step with the NaOH formation in the electrolyte and a Cl2 production step. The first step involves a cathodic H2 evolution reaction (H2O → H2) and an anodic Na+ de-intercalation reaction (Na0.44MnO2 → Na0.44−xMnO2), during which NaOH is produced in the electrolyte solution. The second step depends on a cathodic Na+ intercalation reaction (Na0.44−xMnO2 → Na0.44MnO2) and an anodic Cl2 production (Cl → Cl2). The cycle of the two steps provides a membrane-free process, which is potentially a promising direction for developing clean chlor-alkali technology.

Highlights

Existing chlor-alkali processes generally use asbestos, mercury or fluorine-containing ionexchange membranes to separate the simultaneous chlorine production on the anode and hydrogen production on the cathode, and form sodium hydroxide in the electrolyte
Typical chlor-alkali electrolysis consists of two half reactions: the hydrogen evolution reaction (HER) on the cathode and the chlorine evolution reaction (CER) on the anode, which is accompanied by sodium hydroxide (NaOH) formation in the electrolyte
We report a membrane-free chlor-alkali electrolysis process, where the Cl2 evolution and H2/NaOH production are decoupled by the reversible Na-ion intercalation/de-intercalation reaction of the Na0.44MnO2 electrode

Summary

Introduction

Existing chlor-alkali processes generally use asbestos, mercury or fluorine-containing ionexchange membranes to separate the simultaneous chlorine production on the anode and hydrogen production on the cathode, and form sodium hydroxide in the electrolyte. The general applications of this membranebased chlor-alkali process remain challenging This method can facilitate the separation of the products because of its chemical resistance, the expensive ion exchange membrane generally exhibits limited useful life[20,21,22,23,24,25,26,27]. The old mercury cell can be considered as a typical membrane-free chlor-alkali technology, where the redox mediator of amalgam/sodium amalgam (Hg/ NaHg) decouples the H2 (and NaOH) production and Cl2 production. The reversible Na+ intercalation/de-intercalation of the electrode is expected to be used as a redox mediator to decouple the chlor-alkali technology

Methods

Results

Conclusion