Novel Inorganic Integrated Membrane Electrodes for Membrane Capacitive Deionization

Abstract

In capacitive deionization (CDI), coion repulsion and Faradaic reactions during charging reduce the charge efficiency (CE), thus limiting the salt adsorption capacity (SAC) and energy efficiency. To overcome these issues, membrane CDI (MCDI) based on the enhanced permselectivity of the anode and cathode is proposed using the ion-exchange polymer as the independent membrane or coating. To develop a novel and cost-effective MCDI system, we fabricated an integrated membrane electrode using a thin layer of the inorganic ion-exchange material coated on the activated carbon (AC) electrode, which effectively improves the ion selectivity. Montmorillonite (MT, Al2O9Si3) and hydrotalcite (HT, Mg6Al2(CO3)­(OH)16·4H2O) were selected as the main active anion- and cation-exchange materials, respectively, for the cathode and anode. The HT–MT MCDI system employing HT–AC and MT–AC electrodes obtained a CE of 90.5% and an SAC of 15.8 mg g–1 after 100 consecutive cycles (50 h); these values were considerably higher than those of the traditional CDI system employing pristine AC electrodes (initially, a CE of 55% and an SAC of 10.2 mg g–1, which attenuated continuously to zero, and even “inverted work” occurs after 50 h, i.e., desorption during charging and adsorption during discharging). The HT–MT MCDI system showed moderate tolerance to organic matters during desalination and retained 84% SAC and 89% CE after 70 cycles in 50–200 mg L–1 sodium alginate. This study demonstrates a simple and cost-effective method for fabricating high-CE electrodes for desalination with great application potential.

Metal–Organic Framework with a Redox-Active Bridge Enables Electrochemically Highly Selective Removal of Arsenic from Water

“…For example, directly utilizing redox-active organic ligands to connect the adjacent Fe trinuclear secondary building units can be an effective strategy to shorten the redox-active bridge and thus improve the redox efficiency between multiple active sites. As for the counter electrode, an integrated membrane assembly (i.e., an ion exchange layer coated on the electrode, with the layer thickness being less than 1/10 of the free-standing CEM) can be used as a cost-effective alternative to facilitate the wider application of the proposed technology. , The development of more highly selective and highly conductive platform materials is also critical to improve the selective removal efficiency of As­(III). A new type of iron-based conductive MOF is a potential electrode material.…”

“…As for the counter electrode, an integrated membrane assembly (i.e., an ion exchange layer coated on the electrode, with the layer thickness being less than 1/10 of the free-standing CEM) can be used as a cost-effective alternative to facilitate the wider application of the proposed technology. 62,63 The development of more highly selective and highly conductive platform materials is also critical to improve the selective removal efficiency of As(III). A new type of iron-based conductive MOF is a potential electrode material.…”

Electrode Materials for Desalination of Water via Capacitive Deionization

“…To address this issue, Wu et al attempted to prepare AC electrode coated with a thin layer of ionexchange polymer for mCDI (Figure 9). [120] In this direction, they have employed montmorillonite (MT, Al 2 O 9 Si 3 ) as an anion-exchange material and hydrotalcite (HT, Mg 6 Al 2 -(CO 3 )(OH) 16 .4H 2 O) as a cation-exchange material for the preparation of electrode. A charge efficiency of 90.5 % and SAC value of 15.8 mg g À 1 , compared to the pristine sample (CE of 55 % and SAC of 10.2 mg g À 1 ), suggest the potential of montmorillonite and hydrotalcite as ion exchange materials for the fabrication of high-performance charge efficient electrodes for mCDI.…”

Poly(arylene alkylene)-Based Ion-Exchange Polymers for Enhancing Capacitive Desalination Capacity and Electrode Stability

“…Moreover, the coating method using the membrane precursor solution is feasible to adjust the thickness of the layer, has controllable cost, and can build module integration in scale, playing a crucial role in the industrial realization of MCDI. However, the desalination capacity by IEM coatings achieves only 5–25 mg g –1 and the endurance time is too short or not mentioned in previous reports. − The exploration of high-performance ion-exchange materials for MCDI devices, hence, is necessary and challenging.…”