Efficient and Durable Sodium, Chloride‐doped Iron Oxide‐Hydroxide Nanohybrid‐Promoted Capacitive Deionization of Saline Water via Synergetic Pseudocapacitive Process

Abstract

Recently, the rational design and development of efficient faradaic deionization electrodes with high theoretical capacitance, natural abundance, and attractive conductivity have shown great promise for outstanding capacitive deionization (CDI)‐based desalination applications. Herein, the construction of novel FeOOH hybrid heterostructures with Na and Cl dopants (e.g., Na‐FeOOH and Cl‐FeOOH) via a robust hydrothermal strategy is reported, and an asymmetric CDI cell (Na‐FeOOH//Cl‐FeOOH) comprising Na‐FeOOH and Cl‐FeOOH working as the cathode and anode, respectively, is assembled. The multiple coupling effects of the specific structural features (e.g., enriched porosity, hierarchical pore alignment, and highly open crystalline framework), enhanced electrochemical conductivity, and optimized ion‐transfer property endow the FeOOH hybrid electrode with improved electrochemical performance. Impressively, the Na‐FeOOH//Cl‐FeOOH cell demonstrates a superior salt adsorption capacity (SACNaCl) of 35.12 mg g−1 in a 500 mg L−1 NaCl solution, a faster removal rate, and remarkable cycling stability. Moreover, the pseudocapacitive removal mechanism from the synergetic contribution of the Na‐FeOOH cathode and Cl‐FeOOH anode account for the significant desalination promotion of the Na‐FeOOH//Cl‐FeOOH cell.

Core–shell 2D nanoarchitectures: engineering N, P-doped graphitic carbon/MXene heterostructures for superior capacitive deionization

“…Especially, such a high MSAR value for N, P-GC/ MXene indicated that the desalination of NaCl could be rapidly accomplished in a short time, which was very essential for the desalination process of actual water. 8,9 Furthermore, we also studied the areal SAC of N, P-GC/MXene under different mass loadings. The results presented in Fig.…”

“…[1][2][3][4] Capacitive deionization (CDI) with merits such as low energy consumption, ease of operation, and environmental friendliness, has attracted considerable attention for saline water desalination, especially for low-salinity solutions. [5][6][7][8] Electrode materials are known to play a signicant role in achieving high efficiency, rapid desalination rate, and excellent cycling stability for CDI, and thereby the design and innovation of advanced electrode materials have always been a research hotspot. 9,10 Generally, CDI electrode materials can be divided into two categories: (I) electrochemical double-layer (EDL) capacitive materials, e.g., carbon materials like activated carbon (AC), 11 porous carbon, 12 graphene, 13 and carbon nanotubes (CNTs); 14 (II) pseudocapacitive materials such as metal oxides, 15 suldes, 16 and hydroxides.…”

“…18,19 Nevertheless, some pseudocapacitive materials, which also possess inherent low conductivity and inadequate CDI cycling stability, require further optimization through multiple strategies such as the material composition, morphology, and microstructure regulation, heteroatom doping, or composite engineering. 8,20 MXenes are an emerging group of 2D transition metal carbides and nitrides with a formula M n+1 X n T x , where M represents an early transition metal, X denotes carbon and/or nitrogen, T x stands for the surface terminations, and n ranges from 1 to 3. [21][22][23] Owing to their exceptional metallic conductivity, high hydrophilic surface functionalities, and tunable interlayer spacing, MXenes together with their composites have proven to be promising candidates for facilitating diverse electrochemical applications such as supercapacitors, 24,25 lithium-ion/sulfur batteries, 26,27 and electrocatalysis,.…”

Enhanced Pseudo-Capacitance Process in Nanoarchitectural Layered Double Hydroxide Nanoarrays Hollow Nanocages for Improved Capacitive Deionization Performance

“…Freshwater scarcity heavily harms the sustainable development of society, and energy-efficient technology is therefore critically in demand to tackle this challenge . Capacitive deionization (CDI) is a robust process for producing clean water from brackish water with low energy input and high efficiency. − The most important part of CDI is the electrode, which determines the desalination performance. − In recent years, CDI faradic electrodes emerged as a hot topic due to their strong deionization ability. − While several materials have been explored for the selective removal of sodium (Na + ) ions, faradic materials for the removal of chloride (Cl – ) ions are limited . Materials like Ag and Bi, − which are often used for Cl – capture, face challenges like high costs and poor cycle performance. , …”

Efficient Removal of Chlorine Ions by Ultrafine Fe3C Nanoparticles Encapsulated in a Graphene/N-Doped Carbon Hybrid Electrode: Redox and Confinement Effect

“…In pursuit of efficient and stable CDI performance, many efforts have been focused on the optimization and innovation of devices and electrode materials, suggesting that CDI performance is closely related to electrode materials. , The traditional Cl-storage electrodes are carbon materials based on the electric double-layer mechanism, such as porous carbon, carbon nanotubes, graphene, and so forth. − However, the lower adsorption capacity (3–20 mg g –1 ) and co-ion repulsion effect of carbon materials seriously hinder their further CDI applications. − Recently, several explorations have been made in redox pseudocapacitance-based Cl-storage electrodes, which exhibit stronger electro-absorption capacity, a faster adsorption rate, and better stability. − Particularly, iron-/nitrogen-doped carbon (Fe/NC) hybrid composites with abundant sources, environmental friendliness, high conductivity, and rich valence states have shown great potential as an efficient electrode for batteries, supercapacitors, and CDI applications. − For instance, Wang et al have prepared a Fe–N–C composite that exhibits a desalination capacity of 36.25 mg g –1 and good regeneration ability in 30 cycles . A three-dimensional (3D)-FeNC tube has been constructed for CDI electrodes, which demonstrates a high capacity of 40.70 mg g –1 and stable cycling over 200 cycles .…”