Enhanced Electrodesorption Performance via Cathode Potential Extension during Capacitive Deionization

Jie Fu,Zhumei Sun,Riya Jin,Pengxiao Liu,Yunyan Wang,Ying Li,Haifang Wang,Qingwei Wang

doi:10.3390/app12062874

Abstract

Complete desorption of contaminants from electrode materials is required for the efficient utilization and long service life of capacitive deionization (CDI) but remains a major challenge. The electrodesorption capacity of CDI in the conventional electrode configuration is limited by the narrow electrochemical stability window of water, which lowers the operating potential to approximately 1.2 V. Here, we report a graphite anode–titanium cathode electrode configuration that extends the cathode potential to −1.7 V and provides an excellent (100%) electrodesorption performance, which is maintained after five cycles. The improvement of the cathode potential depends on the redox property of the electrode. The stronger the oxidizability of the anode and reducibility of the cathode, the wider the cathode potential. The complete desorption potential of SO42− predicted by theoretical electrochemistry was the foundation for optimizing the electrode configuration. The desorption efficiency of Cl− depended on the ionic strength and was negligibly affected by circulating velocities above 112 mL min−1. This work can direct the design optimizations of CDI devices, especially for reactors undergoing chemisorption during the electrosorption process.

Highlights

Capacitive deionization (CDI), often referred to as electrosorption, is the process of driving counter ions toward an electrode by applying an electrical potential between two electrodes [1–4]
The Cl− adsorption capacity on granular activated carbon (GAC) increased from 12.76 μmol g−1 to 18.11 μmol g−1 as the anode potential rose from the open-circuit potential (OCP) to 1.2 V, reflecting the formation of an electric double layer between the electrode surface and chloride ions
17% of the residual Cl− failed to desorb from the GAC surface, even after extending the desorption time, implying that 100% desorption is almost impossible by chemical regeneration

Summary

Introduction

Capacitive deionization (CDI), often referred to as electrosorption, is the process of driving counter ions toward an electrode by applying an electrical potential between two electrodes [1–4]. In CDI based on EDL theory, contaminants from the electrodes can be removed by shorting or reversing the electrodes in the absence of chemicals [17]. This scenario is true only in ideal CDI operations, when the amount of charge during adsorption equals that during desorption.

Methods

Results

Conclusion