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

Redox-mediated oxygen evolution reaction: Engineering oxygen vacancies and heterojunctions in CeFeCo-UiO-66/layered double hydroxide via a two-step corrosion strategy

Modifying metal-organic frameworks (MOFs)-based electrocatalysts remains crucial for enhancing oxygen evolution reaction (OER) performance. Although oxygen vacancies (VO) are recognized as important for OER, their concentration control and relationship with catalytic activity remain unclear. In this study, we employ the redox potential difference between Co2+/3+ (0.55 eV) and Ce3+/4+ (1.44 eV) to induce corrosion on iron foam (IF), driving the redox reaction Ce4+ + Co2+ → Ce3+ + Co3+ to generate VO. The VO content can be qualitatively controlled by adjusting corrosion time, as verified by electron paramagnetic resonance (EPR). The CeFeCo-UiO-66/LDH catalyst delivers exceptional catalytic activity (overpotential η = 273 ± 3 mV @ 100 mA cm-2). Combined X-ray photoelectron spectroscopy (XPS), EPR, in-situ Raman, and Density functional theory (DFT) analyses reveal that the redox interaction between Ce and Co generates VO. These VO species facilitate the formation of active CoOOH during the OER. This work offers insights for designing VO engineering strategies in electrocatalytic systems.

Enhanced Capacitive Deionization of Hollow Mesoporous Carbon Spheres/MOFs Derived Nanocomposites by Interface-Coating and Space-Encapsulating Design

Exploring new carbon-based electrode materials is quite necessary for enhancing capacitive deionization (CDI). Here, hollow mesoporous carbon spheres (HMCSs)/metal-organic frameworks (MOFs) derived carbon materials (NC(M)/HMCSs and NC(M)@HMCSs) are successfully prepared by interface-coating and space-encapsulating design, respectively. The obtained NC(M)/HMCSs and NC(M)@HMCSs possess a hierarchical hollow nanoarchitecture with abundant nitrogen doping, high specific surface area, and abundant meso-/microporous pores. These merits are conducive to rapid ion diffusion and charge transfer during the adsorption process. Compared to NC(M)/HMCSs, NC(M)@HMCSs exhibit superior electrochemical performance due to their better utilization of the internal space of hollow carbon, forming an interconnected 3D framework. In addition, the introduction of Ni ions is more conducive to the synergistic effect between ZIF(M)-derived carbon and N-doped carbon shell compared with other ions (Mn, Co, Cu ions). The resultant Ni-1-800-based CDI device exhibits excellent salt adsorption capacity (SAC, 37.82 mg g-1) and good recyclability. This will provide a new direction for the MOF nanoparticle-driven assembly strategy and the application of hierarchical hollow carbon nanoarchitecture to CDI.

Biomimetic Mineralization Synthesis of Flower-Like Cobalt Selenide/Reduced Graphene Oxide for Improved Electrochemical Deionization

Rationally and precisely tuning the composition and structure of materials is a viable strategy to improve electrochemical deionization (EDI) performances, which yet faces enormous challenges. Herein, an eco-friendly biomimetic mineralization synthetic strategy is developed to synthesize the flower-like cobalt selenide/reduced graphene oxide (Bio-CoSe2/rGO) composites and used as advanced sodium ion adsorption electrodes. Benefiting from the slow and controllable reaction kinetics provided by the biomimetic mineralization process, the flower-like CoSe2 is uniformly constructed in the rGO, which is endowed with robust architecture, substantial adsorption sites and rapid charge/ion transport. The Bio-CoSe2/rGO electrode yields the maximum salt adsorption capacity and salt adsorption rate of 56.3 mg g-1 and 5.6 mg g-1 min-1 respectively, and 92.5% capacity retention after 60 cycles. These results overmatch the pristine CoSe2 and irregular granular CoSe2/rGO synthesized by a hydrothermal method, proving the structural superiority of the Bio-CoSe2/rGO composites. Furthermore, the in-depth adsorption kinetics study indicates the chemisorption nature of sodium ion adsorption. The structures of the Bio-CoSe2/rGO composites after long term EDI cycles are intensively studied to unveil the mechanism behind such superior EDI performances. This study offers one effective method for constructing advanced EDI electrodes, and enriches the application of the biomimetic mineralization synthetic strategy.

Engineering Faradaic Electrode Materials for High-Efficiency Water Desalination

Water desalination technologies play a key role in addressing the global water scarcity crisis and ensuring a sustainable supply of freshwater. In contrast to conventional capacitive deionization, which suffers from limitations such as low desalination capacity, carbon anode oxidation, and co-ion expulsion effects of carbon materials, the emerging faradaic electrochemical deionization (FDI) presents a promising avenue for enhancing water desalination performance. These electrode materials employed faradaic charge-transfer processes for ion removal, achieving higher desalination capacity and energy-efficient desalination for high salinity streams. The past decade has witnessed a surge in the advancement of faradaic electrode materials and considerable efforts have been made to explore optimization strategies for improving their desalination performance. This review summarizes the recent progress on the optimization strategies and underlying mechanisms of faradaic electrode materials in pursuit of high-efficiency water desalination, including phase, doping and vacancy engineering, nanocarbon incorporation, heterostructures construction, interlayer spacing engineering, and morphology engineering. The key points of each strategy in design principle, modification method, structural analysis, and optimization mechanism of faradaic materials are discussed in detail. Finally, this work highlights the remaining challenges of faradaic electrode materials and present perspectives for future research.

Thiosalicylic-Acid-Mediated Coordination Structure of Nickel Center via Thermodynamic Modulation for Aqueous Ni-Zn Batteries

Uniquely functional nanocomplexes with rich coordination environments are critical in energy storage. However, the construction of structurally versatile nanocomplexes remains challenging. In this study, a nickel-based complex with structural variations is designed via thermodynamic modulation using a dual-ligand synthesis strategy. A nickel-based nanomaterial (NiSA-SSA-160) with a large specific surface area is synthesized around the competing coordination of the host and guest molecules that differ in terms of the chemical properties of the O and S elements. Concurrently, the coordination environment of NiSA-SSA-160 is investigated via X-ray absorption fine structure spectroscopy. The thiol functional groups synergistically induced an electron-rich Ni structure, thus increasing the electron density of the central atom. The electrochemical performance of an assembled NiSA-SSA-160//Zn@CC battery is shown to improve significantly, with a maximum energy density of 0.54 mWh cm-2 and a peak power density of 49.49 mW cm-2. This study provides a new perspective regarding coordination transformations and offers an idea for the design of functionally rich nanomaterials.

Coordination Confined Silver-Organic Framework for High Performance Electrochemical Deionization

Silver (Ag) is deemed a promising anode material for capacitive deionization (CDI) due to its high theoretical capacity and efficient selectivity to Cl-. However, the strong volume change during the conversion reaction significantly undermines the cycling performance of the Ag electrode. Additionally, achieving well-dispersed Ag in the active matrix is challenging, as Ag electrodes prepared by conventional thermal reduction tend to agglomerate. Herein, the organic linker confinement strategy is proposed, applying metal-organic framework (MOF) chemistry between Ag nodes and organic ligands to construct Ag-based MOF. The uniform dispersion of Ag at the molecular level, confined in the organic matrix, efficiently enhances the utilization of active sites, and strengthens the interfacial stability of Ag. Consequently, the Ag-MOF for the CDI anode exhibits an excellent Cl- removal capacity of 121.52 mg g-1 at 20 mA g-1 in 500 mg L-1 NaCl solution, and a high Ag utilization rate of 60.54%. After 100 cycles, a capacity retention of 96.93% is achieved. Furthermore, the Cl- capture mechanism of Ag-MOF is elucidated through density functional theory (DFT) calculations, ex situ XRD, ex situ Raman and XPS. This ingenious electrode design can offer valuable insights for the development of high-performance conversion electrodes for CDI applications.

Polyoxometalate-Intercalated Tremella-Like CoNi-LDH Nanocomposites for Electrocatalytic Nitrite-Ammonia Conversion

The electrocatalytic reduction of NO2- (NO2RR) holds promise as a sustainable pathway to both promoting the development of emerging NH3 economies and allowing the closing of the NOx loop. Highly efficient electrocatalysts that could facilitate this complex six-electron transfer process are urgently desired. Herein, tremella-like CoNi-LDH intercalated by cyclic polyoxometalate (POM) anion P8W48 (P8W48/CoNi-LDH) prepared by a simple two-step hydrothermal-exfoliation assembly method is proposed as an effective electrocatalyst for NO2- to NH3 conversion. The introduction of POM with excellent redox ability tremendously increased the electrocatalytic performance of CoNi-LDH in the NO2RR process, causing P8W48/CoNi-LDH to exhibit large NH3 yield of 0.369 mmol h-1 mgcat-1 and exceptionally high Faradic efficiency of 97.0% at -1.3 V vs the Ag/AgCl reference electrode in 0.1 M phosphate buffer saline (PBS, pH = 7) containing 0.1 M NO2-. Furthermore, P8W48/CoNi-LDH demonstrated excellent durability during cyclic electrolysis. This work provides a new reference for the application of POM-based nanocomposites in the electrochemical reduction of NO2- to obtain value-added NH3.