Conducting Polymer Hydrogels Research Articles

Conductive and Thermo-Responsive Composite Hydrogels with Poly(N-isopropylacrylamide) and Carbon Nanotubes Fabricated by Two-Step Photopolymerization.

Biocompatible and conductive polymer hydrogels are the subject of intensive research in the bioengineering field because of their use in bioelectronic devices and for the fabrication of electro-responsive tissues and drug delivery systems. In this study, we report the synthesis of conductive composite hydrogels consisting of a poly(N-isopropylacrylamide) (PNIPAM) matrix embedding carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) using a two-step photopolymerization method. Thermo-responsive hydrogels with controlled hydrophilicity and conductivity were prepared by varying the carbon nanotube concentration in the range 0.5-3 wt%. The thermal response of the PNIPAM-based composite hydrogels was measured by differential scanning calorimetry with both ultrapure water and PBS solution as swelling liquid. Results show that the endothermic peak associated with the temperature-induced volume phase transition (VPT) shifts to higher temperatures upon increasing the concentration of the nanotubes, indicating that more energy is required to dissociate the hydrogen bonds of the polymer/filler network. In PBS solution, the swelling ratios and the VPT temperatures of the composite hydrogels are reduced because of salt-induced screening of the oppositely charged polymer/filler assembly, and the electrical resistivity decreases by a factor of 10 with respect to the water-swollen hydrogels.

The monitoring of plant physiology and ecology: From materials to flexible devices

Plant health monitoring has gotten increasing concerns in recent years. Flexible devices offer a more effective mean of monitoring plants. In order to obtain plant information, the relevant physiological and ecological parameters that need to be concerned are summarized in this review. The aim is to provide a more comprehensive and explorable perspective. The research results and progress of flexible devices for plant monitoring in recent years are presented. This paper focuses on conductive materials for flexible device fabrication, including carbon-based materials (e.g. carbon nanotubes (CNTs), graphene), metallic materials (e.g. gold, silver), conductive polymer materials (e.g. polypyrrole, polythiophene), composite materials, biomass materials and hydrogel materials. In the end, we discuss the challenges and future potential of flexible devices for plant sensing at this stage. It is hoped that this will provide further inspiration for research and development of flexible sensing devices in the plant sector.

Soft-hard interface design in super-elastic conductive polymer hydrogel containing Prussian blue analogues to enable highly efficient electrochemical deionization.

The poor cycling stability of faradaic materials owing to volume expansion and stress concentration during faradaic processes limits their use in large-scale electrochemical deionization (ECDI) applications. Herein, we developed a "soft-hard" interface by introducing conducting polymer hydrogels (CPHs), that is, polyvinyl alcohol/polypyrrole (PVA/PPy), to support the uniform distribution of Prussian blue analogues (e.g., copper hexacyanoferrate (CuHCF)). In this design, the soft buffer layer of the hydrogel effectively alleviates the stress concentration of CuHCF during the ion-intercalation process, and the conductive skeleton of the hydrogel provides charge-transfer pathways for the electrochemical process. Notably, the engineered CuHCF@PVA/PPy demonstrates an excellent salt-adsorption capacity of 22.7 mg g-1 at 10 mA g-1, fast salt-removal rate of 1.68 mg g-1 min-1 at 100 mA g-1, and low energy consumption of 0.49 kW h kg-1. More importantly, the material could maintain cycling stability with 90% capacity retention after 100 cycles, which is in good agreement with in situ X-ray diffraction tests and finite element simulations. This study provides a simple strategy to construct three-dimensional conductive polymer hydrogel structures to improve the desalination capacity and cycling stability of faradaic materials with universality and scalability, which promotes the development of high-performance electrodes for ECDI.

PEDOT:PSS hydrogels with high conductivity and biocompatibility for in situ cell sensing.

Conducting polymer hydrogels, especially poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hydrogels, show great promise in soft bioelectronics due to their high conductivity and the ability of electrical coupling with tissues for sensing and stimulation. However, it is challenging to solve the problem of poor biocompatibility of PEDOT:PSS hydrogels due to the existing harsh preparation methods with the use of toxic and harmful reagents. Herein, we report the synthesis of PEDOT:PSS hydrogels with positively charged conductive polymers as a cross-linker and the application of PEDOT:PSS hydrogels as in situ electrochemical sensors for living cells. The conductivities of PEDOT:PSS hydrogels prepared using this method without any toxic or harmful reagents can reach up to 3265 S m-1. The facile synthesis approach with a simple mixture of PEDOT:PSS aqueous solution and the monomers of conductive polymers at room temperature also enables the printability of PEDOT:PSS hydrogels to fabricate patterned electrodes. Moreover, all the proposed PEDOT:PSS hydrogels demonstrated good biocompatibility. The in situ electrochemical detection of dopamine secreted from PC12 cells cultured within PEDOT:PSS hydrogels suggests that our PEDOT:PSS hydrogels with high conductivity and biocompatibility offer great potential for the integration of biosensors within 3D cell culture.

Preparation and characterization of conductive and stretchable MXene-based nanocomposite hydrogels initiated by metal ions

Conductive hydrogels are emerging as an advanced electronic platform for wearable sensors by synergizing the advantageous features of conductivity and flexibility. Especially conductive polymer hydrogels have widespread applications in the fields of catalysis, biomedicine, monitoring, and wearable electronic skin owing to the outstanding strain sensitivity and resilience thereof. Nevertheless, how to maintain the conductivity of hydrogels and electronic skins under strain or deformation remains a significant challenge. To tackle the said bottleneck, a multiple H-bonding MXene-based conductive hydrogel was established in the present study. With the participation of MXene and Fe[Formula: see text] ions, the hydrogel network was strengthened, which might be attributed to the H-bonding among the polymer chain, MXene, and Fe[Formula: see text] ions. Meanwhile, the elongation at break and compression modulus of Poly(vinyl alcohol) (PVA)- M3F hydrogels increased to 513% and 85.6[Formula: see text]kPa compared with the initial PVA hydrogel, respectively. After incorporating Fe[Formula: see text] ions, the PVA-M3F hydrogels exhibited greater conductivity, which was [Formula: see text][Formula: see text]S/cm. Notably, the PVA-M3F hydrogels displayed good resilience, leading to stable conductivity and strain sensitivity. Subsequently, a finger joint was designed to verify the maintenance of conductivity and monitoring behaviors. PVA-M3F conductive hydrogel was found to possess an outstanding capability for electrical signals feedback and was expected to be applied to electronic sensors or monitors. In summary, the introduction of MXene and Fe[Formula: see text] ions into PVA hydrogels can not only tune the conductivity but also have promising prospects as a countermeasure for wearable electronics.

Electro-assisted assembly of conductive polymer and soft hydrogel into core-shell hybrids

Soft hydrogels have become an important class of materials for mimicking and interfacing biological soft tissues with potential applications in drug delivery, tissue engineering and bioelectronics. Creative methods for integrating hydrogels with other materials such as organic conductors are highly desired. Here, we describe the single-step electrosynthesis of PEDOT/alginate into core-shell hybrid structures via an electrochemical-chemical-chemical mechanism. Using a pulsed electropolymerisation protocol, we generated PEDOT in either oxidized or reduced form. By-products of this electrochemical step trigger the chemical reactions for the concomitant assembly of alginate hydrogels. Characterization evidences that PEDOT (core) and alginate (shell) compartments form an electrochemically integrated interface. During growth, both can be loaded with useful cargo. We loaded a negatively charged small molecule and investigated passive and electroactive release mechanisms from the two compartments. Our electro-assisted assembly/crosslinking of integrated PEDOT/alginate hybrids contributes a promising approach to the design of functional interfaces for applications in controlled release and soft electronics.

A general strategy to achieve high-fidelity electron-ion transduction

In a recent study published in <i>Matter</i>, Yao et al. propose a general strategy to resolve the intrinsic conflict among capacitance, conductivity, and mechanical properties in conventional electrode design by rationally designing the porous structure of conducting polymer hydrogel at micro- and nanoscales. Distinct from the inert metal electrodes, the designed conducting polymer hydrogel electrode renders high-fidelity ionic-electronic transduction and interfacial stability, paving the way for developing next-generation ionotronics devices.

Poly (Vinyl Alcohol)/Agar Hydrogel Electrolytes Based Flexible All-in-One Supercapacitors with Conducting Polyaniline/Polypyrrole Electrodes.

The major components of supercapacitor are electrodes and electrolytes which are fabricated using various materials and methods. Hydrogel is one such material that is used in supercapacitors as electrodes and electrolytes or both. Hydrogels are usually described as a soft and porous network of polymer materials that can swell in water because of the hydrophilic nature of its polymer chains, compriseng a 3D structure. It is well known that supercapacitors possess high-power density but low energy density. For enhancing energy density of these electrochemical cells and a boost in its electrochemical performance and specific capacity, binder free conducting polymer hydrogel electrodes have gained immense attention, especially polyaniline (PANI) and polypyrrole (PPy). Therefore, in this work, chemically crosslinked PVA/Agar hydrogel electrolytes have been prepared and employed. Agar has been added in PVA since it is environmentally friendly, biodegradable, and cost-effective natural polymer. Subsequently, the binder free polyaniline/polypyrrole electrodes were grown on the PVA/Agar hydrogel electrolytes to fabricate all-in-one flexible hydrogels. The synthesized hydrogels were characterized using X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) analysis, Field emission scanning electron microscope (FESEM) and mechanical studies. Then, the all-in-one flexible supercapacitors were fabricated using the hydrogels. The electrochemical studies such cyclic voltammetry (CV), galvanic charge discharge (GCD), and electrochemical impedance spectroscopy (EIS) studies. The fabricated all-in-one lamination free supercapacitors showed promising results and by comparing all four samples, PAP2 where 5 mL of PVA was used in combination with 3 mL of Agar and 5 mL of PANI and PPy each, exhibited the highest areal capacitance of 750.13 mF/cm2, energy density of 103.02 μWh/cm2, and 497.22 μW/cm2 power density. The cyclic stability study revealed the 149% capacity retention after 15,000 cycles.

Bioinspired fabrication of self-recovery, adhesive, and flexible conductive hydrogel sensor driven by dynamic borate ester bonds and tannic acid-mediated noncovalent network

Conductive polymer hydrogels have received enormous attention because of their promising applications in healthcare monitoring, soft robots, and wearable electronics. Development of hydrogel sensor with strong mechanical properties, excellent sensing capabilities, self-healing and adhesive properties is highly desirable and still remains a critical challenge. Herein, we report a borax crosslinked flexible hydrogel based on polyvinyl alcohol (PVA), sodium alginate (SA), and tannic acid (TA) modify barium titanate (BT) nanoparticles (T@BT) via a facile one-pot method. The crosslinking network was formed by dynamic reversible borate ester bond and TA-enabled interactions including hydrogen bonds and coordination bonds, which endowed the hydrogel with excellent self-healing and mechanical properties. Meanwhile, the combination of functional catechol groups in TA with the significantly improved cohesion of the hydrogel enabled the hydrogel to exhibit strong and residue-free adhesion to a variety of inorganic and organic materials. The adhesion strength to wood was up to 67.5 kPa. Furthermore, the addition of the T@BT not only rendered the hydrogel highly conductive (1.91 S/m) and sensitive for sensing, but also synergistically enhanced the toughness (587.1 KJ/m3) of the hydrogel. This work provides new ideas for the preparation of multifunctional conductive hydrogels.

Metal-Coordinated Hydrogels As Efficient Oxygen Evolution Electrocatalysts

Conductive polymer hydrogels have large surface area and high conductivity. Their properties can easily be tailored further by functionalizing them with metals and nonmetals. However, the potential of metal-conjugated hydrogels for electrocatalysis has rarely been investigated. In this work, we report the synthesis of transition metals-conjugated polyaniline-phytic acid (PANI-PA) hydrogels that show efficient electrocatalytic properties for the oxygen evolution reaction (OER). Among many transition metals studied, Fe is accommodated by the hydrogel the most because of the favorable affinity of the PA groups in the hydrogel for Fe. Meanwhile, those containing both Fe and Co are found to be the most effective for electrocatalysis of OER. The most optimized such hydrogel, NF@Hgel-Fe0.3Co0.1, which has 3:1 ratio of Fe and Co, needs an overpotential of only 280 mV to catalyze OER with a current density of 10 mV cm-2 in 1 M KOH solution. Furthermore, these metal-doped PANI-PA hydrogels can easily be loaded on nickel foam and carbon cloth via a simple soak-and-dry method to form free-standing electrodes. Overall, the work demonstrates a facile synthesis and fabrication of sustainable OER electrocatalysts and electrodes that are composed of easily processable hydrogels conjugated with various earth-abundant transition metals.Figure R. Schematic illustration of the synthesis of PA-PANI-Metal (Hgel-M x ) hydrogels for electrocatalysis of OER. Figure 1

Ultrastrong, highly conductive and capacitive hydrogel electrode for electron-ion transduction

<h2>Summary</h2> Electron-ion transduction is the cornerstone for promoting emerging ionotronic devices, ranging from basic electronic elements to bioelectronics. However, with commonly used metal electrodes, the electron-ion transduction suffers from high impedance, signal distortion, and poor voltage tolerance. Conductive porous electrodes could partially remedy these issues but are accompanied by mechanical weakness. Herein, a general strategy is discovered to ameliorate these issues by introducing a conducting polymer hydrogel electrode of ultrahigh strength and conductivity with a capacitive behavior. These features are derived from a nanoporous conductive matrix that has π-π interactions as both cross-linking sites and electron-transfer pathways and is formed through surface gelation coupled with chemical treatment and controlled densification. This strategy significantly decreases the low-frequency impedance and improves the signal fidelity, without affecting its high-frequency response. Furthermore, excellent biocompatibility and multifunctionality have also been demonstrated, showing the great potential of this strategy for bioelectronic applications and human-machine interfaces.

Conducting polymer host–guest hydrogels with bicontinuous electron/ion transport for boosted thickness–independent supercapacitance

The development of conducting polymer hydrogels with 3D ordering and hierarchical geometry is urgent yet challenging for the design of electrochemical/electronic systems with combined features of hydrogel structures and pseudocapacitive organic materials. Herein, a host–guest hybrid gel electrode that is composed of a polypyrrole (PPy) aerogel and its skeleton-surface-constrained Fe3+-coordinated poly(acrylic acid) (Fe-PAA) hydrogel is fabricated, which can readily work as a highly elastic and self-healable electrode for an all-gel-state supercapacitor with thickness-independent capacitive performance. An interfacial polymerization approach by restraining oxidative nucleation and promoting secondary growth reactions is presented for preparing the pseudocapacitive PPy aerogel as a host component with good elasticity. Upon an impregnation with the ionically conductive and self-healable Fe-PAA hydrogel as a guest component, the resultant PPy aerogel-hosting hydrogels (PAHH) exhibit a remarkable thickness-independent supercapacitance owing to the enhanced electron/ion transport kinetics induced by a bicontinuous electron/ion-conducting network. A proof-of-concept all-solid-state supercapacitor based on the host–guest hybrid electrodes demonstrates a remarkable remarkably high areal capacitance of 2033 mF cm−2 and extremely steady retention undergoing a 60 % compression deformation and cutting damage with high self-healing performance. The host–guest geometry design for the development of bicontinuous electron/ion conductive transport in conducting polymer-based electrodes might boost unprecedented electron and ion transport in high-mass-loading thick electrodes for smart energy storage devices.

Patternable Gelatin Methacrylate/PEDOT/Polystyrene Sulfonate Microelectrode Coatings for Neuronal Recording.

This manuscript addresses the need for new soft biomaterials that can be fabricated on the surface of microelectrodes to reduce the mechanical mismatch between biological tissues and electrodes and improve the performance at the neural interface. By electrochemical polymerization of poly(3,4-dioxythiophene) (PEDOT)/polystyrene sulfonate (PSS) through a gelatin methacrylate (GelMA) hydrogel, we demonstrate the synthesis of a conducting polymer hydrogel (CPH) to meet the performance criteria of bioelectrodes. The hybrid material can be photolithographically patterned and covalently attached to gold microelectrodes, forming an interpenetrating network, as confirmed by infrared spectroscopy. The GelMA/PEDOT/PSS coatings were found to be reversibly electroactive by cyclic voltammetry and had low impedance compared to bare gold and GelMA-coated microelectrodes. The CPH coatings showed impedance at levels similar to conventional PEDOT/PSS coatings at a frequency of 1000 Hz. CPH exhibited electrochemical stability over 1000 CV cycles, and its performance was maintained over 14 days. Biocompatibility of the CPH coatings was confirmed by primary hippocampal neuronal cultures via a neuronal viability assay. The CPH-coated microelectrode arrays (MEAs) successfully recorded neuronal activity from primary hippocampal neuronal cells. The CPH GelMA/PEDOT/PSS is a highly promising coating material to enhance microelectrode performance at the neural interface.

3D printable conductive polymer hydrogels with ultra-high conductivity and superior stretchability for free-standing elastic all-gel supercapacitors

Conductive polymer hydrogels (CPHs), especially poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) hydrogels, have become research hotspot because they demonstrate tremendous application potential in cutting-edge technologies such as flexible electrochemical energy storage, bioelectronics, and wearable electronics due to their unique electrical, electrochemical and mechanical properties. However, the existing gelation strategies generally fail to achieve excellent electrical and mechanical properties simultaneously in PEDOT:PSS hydrogels and limit their broad applications. Herein, an effective gelation strategy is developed to achieve a kind of free-standing PEDOT:PSS hydrogels by double-additive induced physical cross-linking. Through the interconnection and entanglement between conductive PEDOT nanofibril chains in the physical cross-linking network, the electrical, mechanical and electrochemical properties can be synergistically optimized. The resulting PEDOT:PSS hydrogels simultaneously show ultra-high electrical conductivity, excellent mechanical stretchability, high resilience, low Young’s moduli, superior swelling behavior, and extrusion 3D printability, demonstrating extensive applicability. As proof of concept applications, substrate-free, highly elastic all-gel supercapacitors (SCs) have been fabricated using the resulting PEDOT:PSS hydrogels as electrodes. The SCs exhibit simple structure, facile assembly process, high specific capacitance, excellent energy storage capacity, superior cyclic stability, and arbitrary deformability, holding great promise for wearable electronics.

Interface interaction-mediated design of tough and conductive MXene-composited polymer hydrogel with high stretchability and low hysteresis for high-performance multiple sensing

Conductive hydrogels based on two-dimensional (2D) nanomaterials, MXene, have emerged as promising materials for flexible wearable sensors. In these applications, the integration of high toughness, ultrastretchability, low hysteresis, self-adhesiveness, and multiple sensory functions into one gel is essential. However, serious issues, such as easy restacking and inevitable oxidation of MXene nanosheets in aqueous media and weak interfacial bindings between MXene and the gel network, make it almost impossible to achieve the multiple performances mentioned above. Here we present a conductive MXene-composited polymer (MCP) hydrogel by incorporating gelatin-modified MXene into polyacrylamide (PAAm) hydrogel for the fabrication of multifunctional sensors. The presence of gelatin not only greatly improves the stability of the MXene nanosheets by forming a protective sheath, but also largely enhances the interfacial interactions between the MXene and the hydrogel network as molecular glues. Thus, the MCP hydrogel exhibits a high strength (430 kPa), remarkable stretchability (1100%), low hysteresis (<10% at 500% cyclic tensile), and excellent repeatable adhesion. The resultant MCP hydrogel-based versatile sensors display a high strain sensitivity with a broad working range (gauge factor (GF) = 8.83, up to 1000%), realizing the detection of various human motions. Moreover, the prepared sensors possess superior thermosensitive capacities (1.110/°C) for the measurement of body temperature. This strategy opens horizons to designing high-performance MXene-based hydrogels for advanced sensing platforms.

High-Stretchability, Ultralow-Hysteresis ConductingPolymer Hydrogel Strain Sensors for Soft Machines.

Highly stretchable strain sensors based on conducting polymer hydrogel are rapidly emerging as a promising candidate toward diverse wearable skins and sensing devices for soft machines. However, due to the intrinsic limitations of low stretchability and large hysteresis, existing strain sensors cannot fully exploit their potential when used in wearable or robotic systems. Here, a conductingpolymer hydrogel strain sensor exhibiting both ultimate strain (300%) and negligible hysteresis (<1.5%) is presented. This is achieved through a unique microphase semiseparated network design by compositing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) nanofibers with poly(vinyl alcohol) (PVA) and facile fabrication by combining 3D printing and successive freeze-thawing. The overall superior performances of the strain sensor including stretchability, linearity, cyclic stability, and robustness against mechanical twisting and pressing are systematically characterized. The integration and application of such strain sensor with electronic skins are further demonstrated to measure various physiological signals, identify hand gestures, enable a soft gripper for objection recognition, and remote control of an industrial robot. This work may offer both promising conducting polymer hydrogels with enhanced sensing functionalities and technical platforms toward stretchable electronic skins and intelligent robotic systems.

Cryopolymerization-enabled self-wrinkled polyaniline-based hydrogels for highly stretchable all-in-one supercapacitors.

Conductive polymer hydrogels are attractive due to their combination of high theoretical capacitance, intrinsic electrical conductivity, fast ion transport, and high flexibility for supercapacitor electrodes. However, it is challenging to integrate conductive polymer hydrogels into an all-in-one supercapacitor (A-SC) simultaneously with large stretchability and superior energy density. Here, a self-wrinkled polyaniline (PANI)-based composite hydrogel (SPCH) with an electrolytic hydrogel and a PANI composite hydrogel as the core and sheath, respectively, was prepared through a stretching/cryopolymerization/releasing strategy. The self-wrinkled PANI-based hydrogel exhibited large stretchability (∼970%) and high fatigue resistance (∼100% retention of tensile strength after 1200 cycles at a 200% strain) ascribing to the formation of the self-wrinkled surfaces and the intrinsic stretchability of hydrogels. Upon cutting off the edge connections, the SPCH could directly work as an intrinsically stretchable A-SC maintaining high energy density (70µW h cm-2) and stable electrochemical outputs under a stretchability of 500% strain and a full-scale bending of 180°. After 1000 cycles of 100% strain stretching and releasing processes, the A-SC device could deliver highly stable outputs with high capacitance retention of 92%. This study might provide a straightforward method for fabricating self-wrinkled conductive polymer-based hydrogels for A-SCs with highly deformation-tolerant energy storage.

Conducting Polymer Hydrogel Driven By Sodium Chloride as High Performance Flexible Supercapacitor Electrode

With the rapid development of the wearable devices and flexible supercapacitors (FSCs), urgent demand for electrodes with high specific capacitance and excellent flexibility have been put forward. Herein, a self-standing conducting polymer hydrogel electrode has been successfully synthesized by in situ polymerization of aniline (ANI) in aqueous solution of polyvinyl alcohol (PVA), phytic acid (PA) and sodium chloride (NaCl). The prepared PANI/PVA/NaCl (PPN) hydrogel electrode shows high specific capacitance (1544 mF cm−2 at current density of 1 mA cm−2), good flexibility (elongation at fracture of 110%), satisfactory electrochemical stability (92% capacitance retention after 500 repeated bending cycles) and excellent cycling stability (78.2% capacitance retention after 10000 cycles) due to the uniform 3D interconnected structure driven by NaCl pseudo template. In order to further explore the potential application prospects of the synthesized hydrogel in flexible devices, a series of all-hydrogel-state FSCs are assembled based on the prepared PPN hydrogel electrodes and typical PVA/H2SO4 electrolyte. The assembled FSCs exhibit high energy density of 51.1 μWh cm−2 at power density of 250 μW cm−2 and long-life stability of 81.10% capacitance retention after 10000 charge/discharge cycles. This work provides a new synthesis strategy for the high performance energy storage electrodes and devices.

Solar steam generation by porous conducting polymer hydrogel

A hydrogel prepared with conductive polymer poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) is used as the photothermal material. Water molecules in the PEDOT:PSS hydrogel consumes less energy to evaporate due to the activation of PSS part to water molecules by polymer-water interaction. With a fully wrapped insulation structure to concentrate heat on the SSG surface, the average evaporation rate and the steam evaporation efficiency yield 2.76 kg·m−2·h−1 and 93.2 % under 1 sun illumination intensity, respectively. More importantly, after 30 days of continuous desalination in saline water, the average evaporation rate remains at 2.66 kg·m−2·h−1 in association with neglectable morphology changes. The frameworks of PEDOT carrying positive charges can intercept chlorine anions, which alleviates the blockage of salt particles. The simple fabrication method, efficient energy utilization, and excellent durability make our SSG system promising for practical use.

Metal-Functionalized Hydrogels as Efficient Oxygen Evolution Electrocatalysts.

Conductive polymer hydrogels have large surface areas and electrical conductivities. Their properties can be further tailored by functionalizing them with metals and nonmetals. However, the potential applications of metal-functionalized hydrogels for electrocatalysis have rarely been investigated. In this work, we report the synthesis of transition-metal-functionalized polyaniline-phytic acid (PANI-PA) hydrogels that show efficient electrocatalytic activities for the oxygen evolution reaction (OER). Among the many transition metals studied, Fe is accommodated by the hydrogel the most due to the favorable affinity of the PA groups in the hydrogel for Fe. Meanwhile, those containing both Fe and Co are found to be the most effective electrocatalysts for OER. The most optimized such hydrogel, NF@Hgel-Fe0.3Co0.1, which is made using a solution that has a 3:1 ratio of Fe and Co, needs an overpotential of only 280 mV to catalyze OER in 1 M KOH solution with a current density of 10 mV cm-2. Furthermore, these metal-functionalized PANI-PA hydrogels can easily be loaded on the nickel foam or carbon cloth via a simple soak-and-dry method to generate free-standing electrodes. Overall, this work demonstrates a facile synthesis and fabrication of sustainable and efficient OER electrocatalysts and electrodes that are composed of easily processable hydrogels functionalized with earth-abundant transition metals.