Desalination by Electrodialysis Using a Stack of Patterned Ion‐Selective Hydrogels on a Microfluidic Device

This study reports a novel approach for separation of charged species using anion‐exchange hydrogel (AEH) and cation‐exchange hydrogel (CEH) in a microfluidic device. The capillary line pinning technique, which is applied in this study, enables in situ fabrication of alternating AEH and CEH that are placed in confined compartments. Adjacent enriched and depleted streams are obtained in continuous flow when a potential difference is applied over the hydrogel stack. The desalination performance of the microchip is demonstrated at different salt concentrations (0.01 × 10^?3–1× 10^?3m sodium chloride), potentials (10–100 V), current densities (12–28 A m^?2), and liquid flow rates (0–5 µL min^?1). It is shown that the microchip is able to remove ≈75% of the salt initially present in the depleted outlet streams at inlet stream concentrations of 1 × 10^?3m sodium chloride. Besides desalination, the microchip allows study of ion transport in the ion‐selective hydrogels to elucidate the interplay of transport phenomena at the electrolyte–hydrogel interface during the desalination process.     

An investigation of fluidized bed electrowinning of cobalt using 50 and 1000 Amp cells

50 Amp and 1000 Amp cells equipped with fluidized bed cathodes were used to investigate the electrowinning of cobalt from sulfate solutions. The catholytes employed ranged in cobalt concentration from 100 to 4.8 grams per liter of cobalt and from acid (pH ≏1) to near neutral (pH^-6). Superficial current densities up to 1.09 A cm^-2 were used. The cells were equipped with a nearly impermeable diaphragm, permitting the use of an anolyte of composition different from that of the catholyte. The current efficiency for cobalt deposition (as conveniently determined by measuring the rate of hydrogen evolution), electrical energy consumption, and appearance of the deposit were studied as a function of catholyte composition. Reasonable current efficiencies were observed. The electrical energy consumptions were much higher than that of conventional electrowinning, but this was shown to be due to the anode chamber and diaphragm resistance losses rather than the fluidized cathode. Formerly with the Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA     

An Energy‐Dense Solvent‐Free Dual‐Ion Battery

Ever‐increasing energy demands call for alternative energy storage technologies with balanced performance and cost characteristics to meet current and emerging applications. Dual‐ion batteries (DIBs) are considered particularly attractive owing to the potentially high specific energy, a rich variety of charge carrier combinations, and the applicability of metal‐free cathode and earth‐abundant anode materials. However, their performance falls far below expectations because of a large excess of solvent needed to dissolve electroactive species that induces side reactions and contributes parasitic weight, which penalizes the reversible capacity and cell‐level energy density. Herein, a solvent‐free DIB utilizing a binary alkali metal molten salt based on bis(fluorosulfonyl)amide as the electrolyte to solve these issues is demonstrated. The cell (NaK‐DIB) operates in a temperature range of 90–120 °C and exhibits high theoretical energy densities of 246 Wh kg^?1 and 533 Wh L^?1 based on active materials and capacity‐matched electrolyte, far surpassing those of reported DIBs. Further improvements could realize affordable grid‐scale energy storage.     

Sodium Biphenyl as Anolyte for Sodium–Seawater Batteries

Sodium‐based battery systems have recently attracted increasing research interest due to the abundant resources employed. Among various material candidates for the negative electrode, sodium metal provides the highest capacity of theoretically 1165 mAh g^?1 and a very low redox potential of ?2.71 versus the standard hydrogen electrode. However, the high reactivity of sodium metal toward the commonly used electrolytes results in severe side reactions, including the evolution of gaseous decomposition products, and, in addition, the risk of dendritic sodium growth, potentially causing a disastrous short circuit of the cell. Herein, the use of sodium biphenyl (Na‐BP) as anolyte for the Na–seawater batteries (Na–SWB) is investigated. The catholyte for the open‐structured positive electrode is natural seawater with sodium cations dissolved therein. Remarkably, the significant electronic and ionic conductivities of the Na‐BP anolyte enable a low overpotential for the sodium deposition upon charge, allowing for high capacity and excellent capacity retention for 80 cycles in full Na–SWB. Additionally, the Na‐BP anolyte suppresses gas evolution and dendrite growth by forming a homogeneous surface layer on the metallic negative electrode.     

A High‐Potential Anion‐Insertion Carbon Cathode for Aqueous Zinc Dual‐Ion Battery

Aqueous dual‐ion batteries (DIBs) are promising for large‐scale energy storage due to low cost and inherent safety. However, DIBs are limited by low capacity and poor cycling of cathode materials and the challenge of electrolyte decomposition. In this study, a new cathode material of nitrogen‐doped microcrystalline graphene‐like carbon is investigated in a water‐in‐salt electrolyte of 30 m ZnCl₂, where this carbon cathode stores anions reversibly via both electrical double layer adsorption and ion insertion. The (de)insertion of anions in carbon lattice delivers a high‐potential plateau at 1.85 V versus Zn²⁺/Zn, contributing nearly 1/3 of the capacity of 134 mAh g^?1 and half of the stored energy. This study shows that both the unique carbon structure and concentrated ZnCl₂ electrolyte play critical roles in allowing anion storage in carbon cathode for this aqueous DIB.     

Five-Membered Ring Nitroxide Radical: A New Class of High-Potential,Stable Catholytes for Neutral Aqueous Organic Redox Flow Batteries

The utilization of redox-active and stable cyclic nitroxide radicals (CNRs) holds a great promise in neutral aqueous organic redox flow batteries (AORFBs) for large-scale energy storage. Herein, a new class of CNRs with five-membered ring pyrrolidine and pyrroline motifs for AORFBs is reported. By rational molecular engineering of introducing CC double bond into the pyrrolidine-based molecule, 3-carbamoyl-2,2,5,5-tetramethylpyrroline-1-oxyl (CPL) with a high redox potential of 0.76 V (vs Ag/AgCl) is demonstrated, which is 160 mV higher than the common 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives with a six-membered ring as the core structure. Density functional theory calculations reveal that the much enhanced redox potential for CPL is largely contributed by lowered standard free energy in reduction reaction and charge population sum of N O radical head. When paired with the BTMAP-viologen anolyte, the CPL-based AORFB delivers constant capacity retention of up to 99.96%/cycle over 500 cycles.     

High-Performance Flow Alkali-Al/Acid Hybrid Fuel Cell for High-Rate H2 Generation

Hydrogen (H₂) has been utilized as a versatile feedstock or promising energy carrier in a variety of fields, yet the implementation of high-rate H₂ production presents a grand challenge for its readily accessible application. Herein, a newly alkali-Al/acid hybrid fuel cell (3AHFC) that shows the capability of rapidly producing H₂ upon delivering a considerably high energy density is reported, which is set up by paring Al anode in alkaline anolyte with acidic catholyte and a relatively cheap nanohybrid of Ru nanoparticle decorating crumpled reduced graphene oxide (Ru/c-rGO) as cathode catalysts. It is demonstrated that the 3AHFC can release a power density of up to 240.6 mW cm⁻² with a Faradic efficiency of approaching 99% for fast H₂ generation (300 mA cm⁻²). Such hybrid electrolyte H₂-generation fuel cell can also be extended for either seawater anolyte or metallic Mg anode, presenting great promise for the practice feasibility of on-site H₂ production for applications in tough or even extreme environments.     

Continuously Producing Watersteam and Concentrated Brine from Seawater by Hanging Photothermal Fabrics under Sunlight

Solar‐enabled evaporation for seawater desalination is an attractive, renewable, and environment‐friendly technique, and tremendous progress has been achieved by developing various photothermal membranes. However, traditional photothermal membranes directly float on water, resulting in some limitations such as unavoidable heat‐loss to bulk water and severe salt accumulation. To solve these problems, a hydrophilic, polymer nanorod‐coated photothermal fabric is designed and fabricated, and then an indirect‐contact evaporation system by hanging the fabric is demonstrated. The two ends of the fabric are designed to be in contact with seawater to guide water flow through capillary suction. Both arc‐shaped top/bottom surfaces of the hanging fabrics are exposed to air, which can prevent heat dissipation to bulk seawater and facilitate the double‐surface evaporation upon sunlight irradiation. Our design leads to an efficient evaporation rate of 1.94 kg m^?2 h^?1 and high solar efficiency of 89.9% upon irradiation with sunlight (1.0 kW m^?2). Importantly, the highly concentrated brine can drip from the bottom of the arc‐shaped fabric, without the appearance of solid‐salt accumulation. This indirect‐contact evaporation system establishes a new path to continuously and economically produce watersteam from seawater for fresh‐water and concentrated brine for the chlor‐alkali industry.     

Osmotic Power Generation with Positively and Negatively Charged 2D Nanofluidic Membrane Pairs

In nature, hierarchically assembled nanoscale ionic conductors, such as ion channels and ion pumps, become the structural and functional basis of bioelectric phenomena. Recently, ion‐channel‐mimetic nanofluidic systems have been built into reconstructed 2D nanomaterials for energy conversion and storage as effective as the electrogenic cells. Here, a 2D‐material‐based nanofluidic reverse electrodialysis system, containing cascading lamellar nanochannels in oppositely charged graphene oxide membrane (GOM) pairs, is reported for efficient osmotic energy conversion. Through preassembly modification, the surface charge polarity of the 2D nanochannels can be efficiently tuned from negative (?123 mC m^?2) to positive (+147 mC m^?2), yielding strongly cation‐ or anion‐selective GOMs. The complementary two‐way ion diffusion leads to an efficient charge separation process, creating superposed electrochemical potential difference and ionic flux. An output power density of 0.77 W m^?2 is achieved by controlled mixing concentrated (0.5 m ) and diluted ionic solutions (0.01 m ), which is about 54% higher than using commercial ion exchange membranes. Tandem alternating GOM pairs produce high voltage up to 2.7 V to power electronic devices. Besides simple salt solutions, various complex electrolyte solutions can be used as energy sources. These findings provide insights to construct cascading nanofluidic circuits for energy, environmental, and healthcare applications.     

Sodium Storage Behavior in Natural Graphite using Ether‐based Electrolyte Systems

This work reports that natural graphite is capable of Na insertion and extraction with a remarkable reversibility using ether‐based electrolytes. Natural graphite (the most well‐known anode material for Li–ion batteries) has been barely studied as a suitable anode for Na rechargeable batteries due to the lack of Na intercalation capability. Herein, graphite is not only capable of Na intercalation but also exhibits outstanding performance as an anode for Na ion batteries. The graphite anode delivers a reversible capacity of ≈150 mAh g^?1 with a cycle stability for 2500 cycles, and more than 75 mAh g^?1 at 10 A g^?1 despite its micrometer‐size (≈100 μm). An Na storage mechanism in graphite, where Na⁺‐solvent co‐intercalation occurs combined with partial pseudocapacitive behaviors, is revealed in detail. It is demonstrated that the electrolyte solvent species significantly affect the electrochemical properties, not only rate capability but also redox potential. The feasibility of graphite in a Na full cell is also confirmed in conjunction with the Na_1.5VPO_4.8F_0.7 cathode, delivering an energy of ≈120 Wh kg^?1 while maintaining ≈70% of the initial capacity after 250 cycles. This exceptional behavior of natural graphite promises new avenues for the development of cost‐effective and reliable Na ion batteries.     

Lubricant-Interface Induced Mobile Crystallization for Hypersaline Wastewater Management

Hypersaline wastewater management is a crucial issue for water-energy nexus. Evaporation-based zero liquid discharge (ZLD) desalination shows great promise to detoxify the hypersaline wastewater. However, salt formed on the evaporation surface compromises the efficiency and continuity of desalination. Here, the study reports a photothermal lubricant-infused surface (PLIS), capable of inducing mobile salt crystallization and eliminating salt scaling during desalination. Few nuclei initiate away from the PLIS, followed by migration inward as salt growth, leading to compact crystal. The final dewetting process leaves only scattered protrusions from crystal bottom contacting with the PLIS. Such a converged small area plus pinpoint contacting mode produce an ultralow adhesion of salt to the substrate (≈2 mN mg⁻¹), ≈40 times lower than that on a regular-used hydrophobic surface. The salt crystal precipitated on the PLIS can be blown off easily by air flow, refreshing the evaporating surface for continuous desalination and realizing ZLD.     

ZnCl2 “Water‐in‐Salt” Electrolyte Transforms the Performance of Vanadium Oxide as a Zn Battery Cathode

Zn batteries potentially offer the highest energy density among aqueous batteries that are inherently safe, inexpensive, and sustainable. However, most cathode materials in Zn batteries suffer from capacity fading, particularly at a low current rate. Herein, it is shown that the ZnCl₂ “water‐in‐salt” electrolyte (WiSE) addresses this capacity fading problem to a large extent by facilitating unprecedented performance of a Zn battery cathode of Ca_0.20V₂O₅?0.80H₂O. Upon increasing the concentration of aqueous ZnCl₂ electrolytes from 1 m to 30 m, the capacity of Ca_0.20V₂O₅?0.80H₂O rises from 296 mAh g^?1 to 496 mAh g^?1; its absolute working potential increases by 0.4 V, and most importantly, at a low current rate of 50 mA g^?1, that is, C/10; its capacity retention increases from 8.4% to 51.1% over 100 cycles. Ex situ characterization results point to the formation of a new ready‐to‐dissolve phase on the electrode in the dilute electrolyte. The results demonstrate that the Zn‐based WiSE may provide the underpinning platform for the applications of Zn batteries for stationary grid‐level storage.     

Modular Deformable Steam Electricity Cogeneration System with Photothermal,Water, and Electrochemical Tunable Multilayers

Capturing solar energy for thermal conversion in a highly efficient manner for steam‐electricity cogeneration is particularly opportune in the context of optimal solar energy utilization for concurrent water‐energy harvesting. Herein, an integrative photothermal evaporator/thermogalvanic cell with the desired optical, heat, water, and electrochemical management for synergistic steam‐electricity production is reported. Versatile layer by‐layer assembly is employed to integrate a hydrogel/metal‐oxide/polymer into a multilayer film with individually addressable thickness, composition, and structure. As such, the ultimate integrative multilayer film cell demonstrates a unified high surface area and conductive electrodes, broadband absorption, rapid water suction‐ion exchange, and thermal insulation properties. Thus, the designed cell immensely suppresses heat losses, achieving a high solar thermal conversion efficiency of 91.4% and maximum power outputs of ≈1.6 mW m^?2. Additionally, the self‐floating, deformable, modular integral device presents appealing attributes such as salt‐rejection for viable seawater desalination, high mechanical stability, and resilience to demanding operating conditions, and configurable on‐demand/point‐of‐use tandem structure to maximize clean water and power generation value per area. This integrated strategy may provide prospective opportunities to reduce dependence on fossil fuels and freshwater inputs and solutions for renewable and decentralized clean water and electricity.     

Metal (Ni,Co)‐Metal Oxides/Graphene Nanocomposites as Multifunctional Electrocatalysts

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) along with hydrogen evolution reaction (HER) have been considered critical processes for electrochemical energy conversion and storage through metal‐air battery, fuel cell, and water electrolyzer technologies. Here, a new class of multifunctional electrocatalysts consisting of dominant metallic Ni or Co with small fraction of their oxides anchored onto nitrogen‐doped reduced graphene oxide (rGO) including Co‐CoO/N‐rGO and Ni‐NiO/N‐rGO are prepared via a pyrolysis of graphene oxide and cobalt or nickel salts. Ni‐NiO/N‐rGO shows the higher electrocatalytic activity for the OER in 0.1 m KOH with a low overpotential of 0.24 V at a current density of 10 mA cm^?2, which is superior to that of the commercial IrO₂. In addition, it exhibits remarkable activity for the HER, demonstrating a low overpotential of 0.16 V at a current density of 20 mA cm^?2 in 1.0 m KOH. Apart from similar HER activity to the Ni‐based catalyst, Co‐CoO/N‐rGO displays the higher activity for the ORR, comparable to Pt/C in zinc‐air batteries. This work provides a new avenue for the development of multifunctional electrocatalysts with optimal catalytic activity by varying transition metals (Ni or Co) for these highly demanded electrochemical energy technologies.     

Sponge‐Templated Preparation of High Surface Area Graphene with Ultrahigh Capacitive Deionization Performance

Capacitive deionization (CDI) is a competent water desalination technique offering an appropriate route to obtain clean water. However, a rational designed structure of the electrode materials is essentially required for achieving high CDI performance. Here, a novel sponge‐templated strategy is developed for the first time to prepare graphene sheets with high specific surface area and suitable pore size distribution. Sponge is used as the support of graphene oxide to prevent the restack of graphene sheets, as well as to suppress the agglomerate during the annealing process. Importantly, the as‐fabricated graphene sheets possess high specific surface area of 305 m² g^?1 and wide pore size distribution. Ultrahigh CDI performance, a remarkable electrosorptive capacity of 4.95 mg g^?1, and siginificant desorption rate of 25 min, is achieved with the sponge‐templated prepared graphene electrodes. This work provides an effective solution for the synthesis of rational graphene architectures for general applications in CDI, energy storage and conversion.     

Kinetically Controlled Coprecipitation for General Fast Synthesis of Sandwiched Metal Hydroxide Nanosheets/Graphene Composites toward Efficient Water Splitting

The development of cost‐effective and applicable strategies for producing efficient oxygen evolution reaction (OER) electrocatalysts is crucial to advance electrochemical water splitting. Herein, a kinetically controlled room‐temperature coprecipitation is developed as a general strategy to produce a variety of sandwich‐type metal hydroxide/graphene composites. Specifically, well‐defined α‐phase nickel cobalt hydroxide nanosheets are vertically assembled on the entire graphene surface (NiCo‐HS@G) to provide plenty of accessible active sites and enable facile gas escaping. The tight contact between NiCo‐HS and graphene promises effective electron transfer and remarkable durability. It is discovered that Ni doping adjusts the nanosheet morphology to augment active sites and effectively modulates the electronic structure of Co center to favor the adsorption of oxygen species. Consequently, NiCo‐HS@G exhibits superior electrocatalytic activity and durability for OER with a very low overpotential of 259 mV at 10 mA cm^?2. Furthermore, a practical water electrolyzer demonstrates a small cell voltage of 1.51 V to stably achieve the current density of 10 mA cm^?2, and 1.68 V to 50 mA cm^?2. Such superior electrocatalytic performance indicates that this facile and manageable strategy with low energy consumption may open up opportunities for the cost‐effective mass production of various metal hydroxides/graphene nanocomposites with desirable morphology and competing performance for diverse applications.     

In Situ Preparation of Sandwich MoO3/C Hybrid Nanostructures for High‐Rate and Ultralong‐Life Supercapacitors

This work presents a design of sandwich MoO₃/C hybrid nanostructure via calcination of the dodecylamine‐intercalated layered α‐MoO₃, leading to the in situ production of the interlayered graphene layer. The sample with a high degree of graphitization of graphene layer and more interlayered void region exhibits the most outstanding energy storage performance. The obtained material is capable of delivering a high specific capacitance of 331 F g^?1 at a current density of 1 A g^?1 and retained 71% capacitance at 10 A g^?1. In addition, nearly no discharge capacity decay between 1000 and 10 000 continuous charge–discharge cycles is observed at a high current density of 10 A g^?1, indicating an excellent specific capacitance retention ability. The exceptional rate capability endows the electrode with a high energy density of 41.2 W h kg^?1 and a high power density of 12.0 kW kg^?1 simultaneously. The excellent performance is attributed to the sandwich hybrid nanostructure of MoO₃/C with broad ion diffusion pathway, low charge‐transfer resistance, and robust structure at high current density for long‐time cycling. The present work provides an insight into the fabrication of novel electrode materials with both enhanced rate capability and cyclability for potential use in supercapacitor and other energy storage devices.     

A General Metal‐Organic Framework (MOF)‐Derived Selenidation Strategy for In Situ Carbon‐Encapsulated Metal Selenides as High‐Rate Anodes for Na‐Ion Batteries

On account of increasing demand for energy storage devices, sodium‐ion batteries (SIBs) with abundant reserve, low cost, and similar electrochemical properties have the potential to partly replace the commercial lithium‐ion batteries. In this study, a facile metal‐organic framework (MOF)‐derived selenidation strategy to synthesize in situ carbon‐encapsulated selenides as superior anode for SIBs is rationally designed. These selenides with particular micro‐ and nanostructured features deliver ultrastable cycling performance at high charge–discharge rate and demonstrate ultraexcellent rate capability. For example, the uniform peapod‐like Fe₇Se₈@C nanorods represent a high specific capacity of 218 mAh g^?1 after 500 cycles at 3 A g^?1 and the porous NiSe@C spheres display a high specific capacity of 160 mAh g^?1 after 2000 cycles at 3 A g^?1. The current simple MOF‐derived method could be a promising strategy for boosting the development of new functional inorganic materials for energy storage, catalysis, and sensors.     

Layered P2‐Type K0.65Fe0.5Mn0.5O2 Microspheres as Superior Cathode for High‐Energy Potassium‐Ion Batteries

Potassium‐ion batteries have been regarded as the potential alternatives to lithium‐ion batteries (LIBs) due to the low cost, earth abundance, and low potential of K (?2.936 vs standard hydrogen electrode (SHE)). However, the lack of low‐cost cathodes with high energy density and long cycle life always limits its application. In this work, high‐energy layered P2‐type hierarchical K_0.65Fe_0.5Mn_0.5O₂ (P2‐KFMO) microspheres, assembled by the primary nanoparticles, are fabricated via a modified solvent‐thermal method. Benefiting from the unique microspheres with primary nanoparticles, the K⁺ intercalation/deintercalation kinetics of P2‐KFMO is greatly enhanced with a stabilized cathodic electrolyte interphase on the cathode. The P2‐KFMO microsphere presents a highly reversible potassium storage capacity of 151 mAh g^?1 at 20 mA g^?1, fast rate capability of 103 mAh g^?1 at 100 mA g^?1, and long cycling stability with 78% capacity retention after 350 cycles. A full cell with P2‐KFMO microspheres as cathode and hard carbon as anode is constructed, which exhibits long‐term cycling stability (>80% of retention after 100 cycles). The present high‐performance P2‐KFMO microsphere cathode synthesized using earth‐abundant elements provides a new cost‐effective alternative to LIBs for large‐scale energy storage.     

Self-Assembled Nanofibrous Hydrogels with Tunable Porous Network for Highly Efficient Solar Desalination in Strong Brine

Hydrogel-based solar evaporators (HSEs) emerged as energy-efficient designs for water purification due to the reduced vaporization enthalpy in the hydrated polymeric network. However, it remains challenging for HSEs to achieve stable performance in desalination, partly due to the tradeoff between desired evaporation dynamics and salt tolerance. Here, composite hydrogels with tunable self-assembled nanofiber networks are exploited for the engineering of solar evaporators with both high evaporation performance and resistance to salt accumulation. The nanofibrous hydrogel solar evaporators (NHSEs) present an intrinsic open network with high porosity, above 90%, enabling continuous water channels for efficient mass transfer. Theoretical modeling captures the complex nexus between microstructures and evaporation performance by coupling water transfer, thermal conduction, and vaporization enthalpy during evaporation. The mechanistic understanding and engineering tuning of the composites lead to an optimum configuration of NHSEs, which demonstrate a stable evaporation rate of 2.85 kg m⁻² h⁻¹ during continuous desalination in 20% brine. The outstanding performance of NHSEs and the underlying design principles may facilitate further development of practical desalination systems.