Enhanced salt removal performance of flow-electrode capacitive deionization via NaOH activation of coffee waste-derived carbonaceous electrodes: Roles of surface textural features

Frequency analysis and resonant operation for efficient capacitive deionization

Magnetic-assisted strategy for performance enhancement of flow-by capacitive deionization

A study of the effect of carbon characteristics on capacitive deionization (CDI) performance

Water scarcity is one of the most severe global challenges in our generation. Electrochemical capacitive deionization (CDI), a green water desalination system, has emerged as a promising technology for producing clean water due to its low energy consumption and environmentally friendly. Prussian blue analogues (PBAs), a class of coordination compounds which can accommodate Na+ ions into their nanoscale interspaces of skeleton frameworks, promise their extraordinary functionalities in CDI technology. Volume expansion that occurs during the ion-insertion/extraction process and inherent low conductivity of PBA electrodes, however, still inevitably lead to their sluggish desalination kinetics and capacity fading. Herein, preparation of trimetallic PBA containing copper, cobalt, and iron with nanoframe superstructures (CuCoFe-PBA NFs) via a multi-step in-situ structural conversion is reported. Comparable experiments indicate that successful conversion via this route is attributable to a self-templated epitaxial growth triggered by the additional introduction of Cu ions into the reaction system. The optimal composition and three-dimensional (3D) opened nanoframe structure of CuCoFe-PBA NFs offer the electrode with rich redox active species, abundant accessible adsorption sites, and fast ion transport that enhance its capacitive deionization (CDI) performance. As a result, the CuCoFe-PBA NFs demonstrate an exceptional CDI performance with a desalination capacity of 46.8 mg g-1 at an applied potential of 1.4 V and superior cyclability with negligible decay on the desalination capacity even after 100 cycle tests. Figure 1

Integrating MnO2 with carbon is a reliable strategy to improve capacitive deionization (CDI) performance by leveraging the unique properties of both components (i.e., MnO2 and carbon). However, the influences of preliminary functionalization of carbon (e.g., nitrogen doping, KOH activation) and pairing of cathodes and anodes on the CDI performance have yet to be systematically explored. Herein, we prepared a group of MnO2-decorated mesoporous carbon composites with nitrogen as a dopant (i.e., MK-NMCS, K-NMCS, NMCS, and CS), and systematically evaluated the desalination performance of various cathode//anode pairs in a hybrid capacitive deionization (HCDI) for capturing Na+, Cu2+, and Pb2+, respectively. Of all electrodes, the MK-NMCS//K-NMCS pair demonstrates the optimum desalination performance based on salt adsorption capacity (SAC) and cycling stability, offering a SAC of 25.4 mg g-1 and a SAC retention of 102.4% after 50 consecutive charge-discharge cycles at 1.2 V in 500 ppm of NaCl solution. In addition, the MK-NMCS//K-NMCS electrodes also show the maximum ion adsorption capacity (IAC) toward Cu2+ and Pb2+ ions compared to other cathode//anode pairs, attaining an IAC of 37.0 and 30.0 mg Cu2+ per gram electrode materials at 1.2 V in 500 and 200 ppm of Cu2+ solutions, respectively (cf. 32.2 mg of Pb2+ per gram of electrode materials in 200 ppm of Pb2+ solution). Besides, these electrodes exhibit excellent cycling stability when applied in removing each heavy metal ion separately, with IAC retentions of 90.0 and 98.5% after 50 cycles toward Cu2+ and Pb2+ ions, respectively. Mechanical analysis reveals that both heavy metals are likely to be sequestered via capacitive electrosorption by carbon, intercalation with MnO2, and surface complexation at the external surface of the [MnO6] octahedral layers. Our results demonstrated a great potential of the MnO2-decorated N-doped carbon//prefunctionalized carbon pairs, in particular, the MK-NMCS//K-NMCS electrode pair for capturing heavy metal ions via HCDI platforms. Such prefunctionalization and pairing strategies are very promising for screening high-performance composite electrodes for wastewater remediation.

Optimizing the energetic performance of capacitive deionization devices with unipolar and bipolar connections under constant current charging

Capacitive deionization with Ca-alginate coated-carbon electrode for hardness control

Optimized desalination performance of high voltage flow-electrode capacitive deionization by adding carbon black in flow-electrode

Enhanced salt removal performance of flow electrode capacitive deionization with high cell operational potential

Water desalination performance of capacitive deionization (CDI) largely depends on electrode materials properties. Rational design and regulation of the structure and composition of electrode materials to acquire high CDI performance is of great significance. Herein, nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) were investigated as electrode material for CDI application. To understand the effect of structure and composition on CDI performance, another two CDI electrode materials, i.e., hollow mesoporous carbon spheres (HMCSs) and solid mesoporous carbon spheres (SMCSs) were prepared for comparison. The obtained N-HMCSs possessed unique hollow cavity and excellent nitrogen doping property, resulting in fast ion diffusion, good charge transfers ability and fine wettability. Compared with HMCSs and SMCSs electrodes, N-HMCSs electrode exhibited an improved electrosorption capacity and rate, demonstrating the dependence of CDI performance on the synergistic effect of hollow structure and nitrogen ...

Carbon nanotubes/activated carbon hybrid as a high-performance suspension electrode for the electrochemical desalination of wastewater

Analysis of the desalting performance of flow-electrode capacitive deionization under short-circuited closed cycle operation

Capacitive deionization (CDI) using a flow-electrode primarily composed of porous materials and an aqueous electrolyte, exhibits continuous deionization and a high desalting efficiency. The development of flow-electrodes with high capacitance and low resistance is essential for achieving an efficient flow-electrode capacitive deionization (FCDI) system with low energy consumption. For this purpose, studies on conductive additives (CAs) that do not clog the flow-channel must be conducted. Here, we evaluated the desalting performance of flow-electrodes with spherical and plate-type conductive additives having sizes between 1 and 10 μm and possessing powder conductivities similar to or higher than nano-sized carbon black, which is often used as the CA in solid fixed electrodes in conventional CDI systems. We confirmed that plate-shaped CAs reduced resistance near the pores and enhanced the desalting performance of the flow-electrodes in FCDI systems. The positive effect of such plate-shaped CAs appears to originate from efficient charge percolation between the ACs via the electrical conductive direction of the graphite and the alignment of the exposed graphite edges to the pumping direction of the flow-electrode. Finally, we verified that the flow-electrode with the newly discovered micro-sized CA could be operated without clogging the flow-channel in FCDI and showed an improved desalting performance of around 1.5 times compared the flow-electrode without the micro-sized CA for extended periods of time.

A newly designed graphite-polyaniline composite current collector to enhance the performance of flow electrode capacitive deionization

The desalination performance of flow electrode capacitive deionization (FCDI) is determined by the ion adsorption on the powdered activated carbon (PAC) and the electron transfer between the current collector and PAC. However, a comprehensive understanding of rate-limiting steps is lacking, let alone to enhance FCDI desalination by regulating the PAC characteristics. This study showed that the electron transfer between PAC and the current collector on the anode side was the rate-limiting step of FCDI desalination. Compared with W900, the desalination performance of FCDI decreased by 95% when W1200 with weak electron transfer ability was used as a flow electrode. The PAC selected in this study transferred electrons directly through the conductive carbon matrix in FCDI and was mainly affected by graphitization. The desalination performance of FCDI was improved by 20 times when the graphitization degree of PAC increased from 0.69 to 1.03. The minimum energy required for electrons to escape from the PAC surface was reduced by the high degree of graphitization, from 4.27 to 3.52 eV, thus improving the electron transfer capacity of PAC on the anode side. This study provides a direction for the optimization of flow electrodes and further promotes the development of FCDI.