Electrosynthesis of chlorine from seawater-like solution through single-atom catalysts.

The chlor-alkali process plays an essential and irreplaceable role in the modern chemical industry due to the wide-ranging applications of chlorine gas. However, the large overpotential and low selectivity of current chlorine evolution reaction (CER) electrocatalysts result in significant energy consumption during chlorine production. Herein, we report a highly active oxygen-coordinated ruthenium single-atom catalyst for the electrosynthesis of chlorine in seawater-like solutions. As a result, the as-prepared single-atom catalyst with Ru-O4 moiety (Ru-O4 SAM) exhibits an overpotential of only ~30 mV to achieve a current density of 10 mA cm-2 in an acidic medium (pH = 1) containing 1 M NaCl. Impressively, the flow cell equipped with Ru-O4 SAM electrode displays excellent stability and Cl2 selectivity over 1000 h continuous electrocatalysis at a high current density of 1000 mA cm-2. Operando characterizations and computational analysis reveal that compared with the benchmark RuO2 electrode, chloride ions preferentially adsorb directly onto the surface of Ru atoms on Ru-O4 SAM, thereby leading to a reduction in Gibbs free-energy barrier and an improvement in Cl2 selectivity during CER. This finding not only offers fundamental insights into the mechanisms of electrocatalysis but also provides a promising avenue for the electrochemical synthesis of chlorine from seawater electrocatalysis.

A polymeric hydrogel electrocatalyst for direct water oxidation.

Metal-free electrocatalysts represent a main branch of active materials for oxygen evolution reaction (OER), but they excessively rely on functionalized conjugated carbon materials, which substantially restricts the screening of potential efficient carbonaceous electrocatalysts. Herein, we demonstrate that a mesostructured polyacrylate hydrogel can afford an unexpected and exceptional OER activity - on par with that of benchmark IrO2 catalyst in alkaline electrolyte, together with a high durability and good adaptability in various pH environments. Combined theoretical and electrokinetic studies reveal that the positively charged carbon atoms within the carboxylate units are intrinsically active toward OER, and spectroscopic operando characterizations also identify the fingerprint superoxide intermediate generated on the polymeric hydrogel backbone. This work expands the scope of metal-free materials for OER by providing a new class of polymeric hydrogel electrocatalysts with huge extension potentials.

Polymeric Single-Ion Conductors with Enhanced Side-Chain Motion for High-Performance Solid Zinc-Ion Batteries.

Zn-based solid polymer electrolytes (SPEs) have enormous potential in realizing high-performance zinc-ion batteries. Polymeric single-ion conductor (PSIC)-based SPEs can largely eradicate anion migration and side reactions of electrodes with decreased polarization, but the ionic conductivity is still unsatisfactory due to the tight localized ion interactions and sluggish chain motion. Herein, by employing the heterocyclic tetrazole as the anionic center of the side chain, a novel PSIC is fabricated with optimized charge delocalization and enhanced side-chain motion. The as-prepared PSIC delivers an ionic conductivity up to 5.4 × 10-4 S cm-1 with an ultrahigh Zn2+ transference number of 0.94. Based on the PSIC, dendrite-free and hydrogen-free Zn plating/stripping cycling (2000 h) is achieved. A further assembled Zn‖V2 O5 battery exhibits superior performances to other solid ZIBs, including a high discharge capacity, excellent rate capability, and long cycling life. In addition, a remarkable shelf-life (90 d), low self-discharge rate, and good temperature adaptability of the solid battery can be achieved benefiting from the high stability of the SPE during operation. The PSIC-based SPEs with advanced ion-transport structure endow solid ZIBs with significant performance improvement, high safety, and durability.

Cation-Vacancy-Enriched Nickel Phosphide for Efficient Electrosynthesis of Hydrogen Peroxides.

Electrocatalytic hydrogen peroxide (H2 O2 ) synthesis via the two-electron oxygen reduction reaction (2e ORR) pathway is becoming increasingly important due to the green production process. Here, cationic vacancies on nickel phosphide, as a proof-of-concept to regulate the catalyst's physicochemical properties, are introduced for efficient H2 O2 electrosynthesis. The as-fabricated Ni cationic vacancies (VNi )-enriched Ni2- x P-VNi electrocatalyst exhibits remarkable 2e ORR performance with H2 O2 molar fraction of >95% and Faradaic efficiencies of >90% in all pH conditions under a wide range of applied potentials. Impressively, the as-created VNi possesses superb long-term durability for over 50 h, suppassing all the recently reported catalysts for H2 O2 electrosynthesis. Operando X-ray absorption near-edge spectroscopy (XANES) and synchrotron Fourier transform infrared (SR-FTIR) combining theoretical calculations reveal that the excellent catalytic performance originates from the VNi -induced geometric and electronic structural optimization, thus promoting oxygen adsorption to the 2e ORR favored "end-on" configuration. It is believed that the demonstrated cation vacancy engineering is an effective strategy toward creating active heterogeneous catalysts with atomic precision.

Toward Flexible Zinc-Ion Hybrid Capacitors with Superhigh Energy Density and Ultralong Cycling Life: The Pivotal Role of ZnCl2 Salt-Based Electrolytes.

Zinc ion hybrid capacitors (ZIHCs) are promising energy storage devices for emerging flexible electronics, but they still suffer from trade-off in energy density and cycling life. Herein, we show that such a dilemma can be well-addressed by deploying ZnCl2 based electrolytes. Combining experimental studies and density functional theory (DFT) calculations, for the first time, we demonstrate an intriguing chloride ion (Cl- ) facilitated desolvation mechanism in hydrated [ZnCl]+ (H2 O)n-1 (with n=1-6) clusters. Based on this mechanism, a water-in-salt type hydrogel electrolyte filled with ZnCl2 was developed to concurrently improve the energy storage capacity of porous carbon materials and the reversibility of Zn metal electrode. The resulting ZIHCs deliver a battery-level energy density up to 217 Wh kg-1 at a power density of 450 W kg-1 , an unprecedented cycling life of 100 000 cycles, together with excellent low-temperature adaptability and mechanical flexibility.

Electronic Modulation of Nickel Disulfide toward Efficient Water Electrolysis.

Developing highly efficient earth-abundant nickel-based compounds is an important step to realize hydrogen generation from water. Herein, the electronic modulation of the semiconducting NiS2 by cation doping for advanced water electrolysis is reported. Both theoretical calculations and temperature-dependent resistivity measurements indicate the semiconductor-to-conductor transition of NiS2 after Cu incorporation. Further calculations also suggest the advantages of Cu dopant to cathodic water electrolysis by bringing Gibbs free energy of H adsorption at both Ni sites and S sites much closer to zero. It is noteworthy that water dissociation on Cu-doped NiS2 (Cu-NiS2 ) surface is even more favorable than those on NiS2 and Pt(111). Thus, the prepared Cu-NiS2 shows noticeably improved performance toward alkaline hydrogen and oxygen evolution reactions (HER and OER). Specifically, it requires merely 232 mV OER overpotential to drive 10 mA cm-2 ; in parallel with Tafel slopes of 46 mV dec-1 . Regarding HER, an onset overpotential of only 68 mV is achieved. When integrated as both electrodes for water electrolysis, Cu-NiS2 needs only 1.64 V to drive 10 mA cm-2 , surpassing the state-of-the-art Ir/C-Pt/C couple (1.71 V). This work opens up an avenue to engineer low-cost and earth-abundant catalysts performing on par with the noble-metal-based one for water splitting.

A Flexible Rechargeable Zinc-Air Battery with Excellent Low-Temperature Adaptability.

Flexible zinc-air batteries (ZAB) are a promising battery candidate for emerging flexible electronic devices, but the catalysis-based working principle and unique semi-opened structure pose a severe challenge to their overall performance at cold temperature. Herein, we report the first flexible rechargeable ZAB with excellent low-temperature adaptability, based on the innovation of an efficient electrocatalyst to offset the electrochemical performance shrinkage caused by decreased temperature and a highly conductive hydrogel with a polarized terminal group to render the anti-freezing property. The fabricated ZABs show excellent electrochemical performances that outperform those of many aqueous ZABs at room temperature. They also deliver a high capacity of 691 mAh g-1 and an energy density of 798 Wh kg-1 at -20 °C (92.7 % and 87.2 % retention of the room temperature counterparts, respectively), together with excellent flexibility and reverting capability.

1D Supercapacitors for Emerging Electronics: Current Status and Future Directions.

1D supercapacitors (SCs) have emerged as promising candidates to power emerging electronics in recent years because of their unique advantages in energy storage and mechanical flexibility. There are four main research fronts in the development of 1D SCs: 1) enhancing mechanical characteristics, 2) achieving superior electrochemical performance, 3) enabling multiple device integration, and 4) demonstrating multifunctionality. Here, a brief history of 1D SCs is presented and significant research achievements regarding the four fronts identified as the main pillars of the development of 1D SCs are highlighted. The current challenges of the fabrication and utilization of 1D SCs are critically examined and potential solutions are analyzed. Plus, the performance inconsistencies arising from the improper use and extreme diversity of performance evaluation and reporting methods are highlighted. Beyond, perspectives on future efforts are provided and goals regarding the four research fronts are set, to further push 1D SCs toward practical applications. The development of 1D SCs is summarized here, with existing obstacles diagnosed, corresponding solutions proposed, and future directions indicated accordingly.

Flexible Zinc-Ion Hybrid Fiber Capacitors with Ultrahigh Energy Density and Long Cycling Life for Wearable Electronics.

Emerging wearable electronics require flexible energy storage devices with high volumetric energy and power densities. Fiber-shaped capacitors (FCs) offer high power densities and excellent flexibility but low energy densities. Zn-ion capacitors have high energy density and other advantages, such as low cost, nontoxicity, reversible Faradaic reaction, and broad operating voltage windows. However, Zn-ion capacitors have not been applied in wearable electronics due to the use of liquid electrolytes. Here, the first quasisolid-state Zn-ion hybrid FC (ZnFC) based on three rationally designed components is demonstrated. First, hydrothermally assembled high surface area and conductive reduced graphene oxide/carbon nanotube composite fibers serve as capacitor-type positive electrodes. Second, graphite fibers coated with a uniform Zn layer work as battery-type negative electrodes. Third, a new neutral ZnSO4 -filled polyacrylic acid hydrogel act as the quasisolid-state electrolyte, which offers high ionic conductivity and excellent stretchability. The assembled ZnFC delivers a high energy density of 48.5 mWh cm-3 at a power density of 179.9 mW cm-3 . Further, Zn dendrite formation that commonly happens under high current density is efficiently suppressed on the fiber electrode, leading to superior cycling stability. Multiple ZnFCs are integrated as flexible energy storage units to power wearable devices under different deformation conditions.

Flexible Waterproof Rechargeable Hybrid Zinc Batteries Initiated by Multifunctional Oxygen Vacancies-Rich Cobalt Oxide.

Although both are based on Zn, Zn-air batteries and Zn-ion batteries are good at energy density and power density, respectively. Here, we adopted Ar-plasma to engrave a cobalt oxide with abundant oxygen vacancies (denoted as Co3O4- x). The introduction of oxygen vacancies to cobalt oxide not only promotes its reversible Co-O ↔ Co-O-OH redox reaction but also leads to good oxygen reduction reaction and oxygen evolution (ORR/OER) performance (a half-wave potential of 0.84 V, four-electron transfer process for ORR, and 330 mV overpotential, 58 mV·dec-1 Tafel slope for OER). We then constructed a battery system based on both Zn-Co3O4- x and Zn-air electrochemical reactions. The hybrid battery reveals both a high-power density of 3200 W·kg-1 and high-energy density of 1060 Wh·kg-1. Furthermore, the developed flexible solid-state hybrid batterydemonstrates good waterproof and washable ability (99.2% capacity retention of after 20 h water soaking test and 93.2% capacity retention after 1 h washing test). Interestingly, the fabricated flexible battery can work under water, and after the power is exhausted, the battery can automatically recover electricity output as long as it is exposed to air. The developed device is suitable for wearable applications considering its electrochemical performances, great environmental adaptation, and "air recoverability". In addition, this study underscores the approach to develop hybrid energy-storage technologies through modification of electrode materials.

A Wearable Supercapacitor Engaged with Gold Leaf Gilding Cloth Toward Enhanced Practicability.

Flexible energy storage devices have attracted wide attention because of the increasing requirement of wearable electronics. However, comfortability, productivity, and feasibility, to name a few, are still far from satisfactory in the current wearable supercapacitors (SCs). This is largely due to the missing of an ideal low-cost flexible substrate/current collector that should not only exhibit high conductivity, but also be compatible with modern textile technologies. Herein, we apply the traditional gilding technique to cloth and successfully convert the cloth to be an excellent current collector which is available at a reasonable cost and compatible with textile technologies. Thanks to the strong electrostatic interaction, we found that a positively charged gold leaf could be laminated on a negatively charged polyester cloth intimately. This substrate could perfectly act as an integrated compact electrode after the electrodeposition of polypyrrole nanorods. The resulting electrode is mechanically strong enough to withstand the tortures of repeated bending, cutting, or puncturing, and is readily assembled into wearable SCs and energy cloth with outstanding practicability, for example, safety and breathability. It is foreseeable that our work will inspire a series design of wearable electronics based on the fascinating gilding art.

Waterproof and Tailorable Elastic Rechargeable Yarn Zinc Ion Batteries by a Cross-Linked Polyacrylamide Electrolyte.

Emerging research toward next-generation flexible and wearable electronics has stimulated the efforts to build highly wearable, durable, and deformable energy devices with excellent electrochemical performances. Here, we develop a high-performance, waterproof, tailorable, and stretchable yarn zinc ion battery (ZIB) using double-helix yarn electrodes and a cross-linked polyacrylamide (PAM) electrolyte. Due to the high ionic conductivity of the PAM electrolyte and helix structured electrodes, the yarn ZIB delivers a high specific capacity and volumetric energy density (302.1 mAh g-1 and 53.8 mWh cm-3, respectively) as well as excellent cycling stability (98.5% capacity retention after 500 cycles). More importantly, the quasi-solid-state yarn ZIB also demonstrates superior knittability, good stretchability (up to 300% strain), and superior waterproof capability (high capacity retention of 96.5% after 12 h underwater operation). In addition, the long yarn ZIB can be tailored into short ones, and each part still functions well. Owing to its weavable and tailorable nature, a 1.1 m long yarn ZIB was cut into eight parts and woven into a textile that was used to power a long flexible belt embedded with 100 LEDs and a 100 cm2 flexible electroluminescent panel.

Single-Site Active Iron-Based Bifunctional Oxygen Catalyst for a Compressible and Rechargeable Zinc-Air Battery.

The exploitation of a high-efficient, low-cost, and stable non-noble-metal-based catalyst with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) simultaneously, as air electrode material for a rechargeable zinc-air battery is significantly crucial. Meanwhile, the compressible flexibility of a battery is the prerequisite of wearable or/and portable electronics. Herein, we present a strategy via single-site dispersion of an Fe-Nx species on a two-dimensional (2D) highly graphitic porous nitrogen-doped carbon layer to implement superior catalytic activity toward ORR/OER (with a half-wave potential of 0.86 V for ORR and an overpotential of 390 mV at 10 mA·cm-2 for OER) in an alkaline medium. Furthermore, an elastic polyacrylamide hydrogel based electrolyte with the capability to retain great elasticity even under a highly corrosive alkaline environment is utilized to develop a solid-state compressible and rechargeable zinc-air battery. The creatively developed battery has a low charge-discharge voltage gap (0.78 V at 5 mA·cm-2) and large power density (118 mW·cm-2). It could be compressed up to 54% strain and bent up to 90° without charge/discharge performance and output power degradation. Our results reveal that single-site dispersion of catalytic active sites on a porous support for a bifunctional oxygen catalyst as cathode integrating a specially designed elastic electrolyte is a feasible strategy for fabricating efficient compressible and rechargeable zinc-air batteries, which could enlighten the design and development of other functional electronic devices.

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes.

Thermal runaway has been a long-standing safety issue impeding the development of high-energy-density batteries. Physical safety designs such as employing circuit-breakers and fuses to batteries are limited by small operating voltage windows and no resumption of original working condition when it is cooled down. Here we report a smart thermoresponsive polymer electrolyte that can be incorporated inside batteries to prevent thermal runaway via a fast and reversible sol-gel transition, and successfully combine this smart electrolyte with a rechargeable Zn/α-MnO2 battery system. At high temperature, battery operation is inhibited as a result of the increased internal resistance caused by the gelation of liquid electrolyte. After cooling down, the electrolyte is spontaneously reversed to sol state and the electrochemical performance of the battery is restored. More importantly, sol-gel transition enables the smart battery to experience different charge-discharge rates under various temperature levels, providing a smart and active strategy to achieve dynamic and reversible self-protection.

Recent Progress on Flexible and Wearable Supercapacitors.

Recently, wearable electronic devices including electrical sensors, flexible displays, and health monitors have received considerable attention and experienced rapid progress. Wearable supercapacitors attract tremendous attention mainly due to their high stability, low cost, fast charging/discharging, and high efficiency; properties that render them value for developing fully flexible devices. In this Concept, the recent achievements and advances made in flexible and wearable supercapacitors are presented, especially highlighting the promising performances of yarn/fiber-shaped and planar supercapacitors. On the basis of their working mechanism, electrode materials including carbon-based materials, metal oxide-based materials, and conductive polymers with an emphasis on the performance-optimization method are introduced. The latest representative techniques and active materials of recently developed supercapacitors with superior performance are summarized. Furthermore, the designs of 1D and 2D electrodes are discussed according to their electrically conductive supporting materials. Finally, conclusions, challenges, and perspective in optimizing and developing the electrochemical performance and function of wearable supercapacitors for their practical utility are addressed.

Weavable, Conductive Yarn-Based NiCo//Zn Textile Battery with High Energy Density and Rate Capability.

With intrinsic safety and much higher energy densities than supercapacitors, rechargeable nickel/cobalt-zinc-based textile batteries are promising power sources for next generation personalized wearable electronics. However, high-performance wearable nickel/cobalt-zinc-based batteries are rarely reported because there is a lack of industrially weavable and knittable highly conductive yarns. Here, we use scalably produced highly conductive yarns uniformly covered with zinc (as anode) and nickel cobalt hydroxide nanosheets (as cathode) to fabricate rechargeable yarn batteries. They possess a battery level capacity and energy density, as well as a supercapacitor level power density. They deliver high specific capacity of 5 mAh cm-3 and energy densities of 0.12 mWh cm-2 and 8 mWh cm-3 (based on the whole solid battery). They exhibit ultrahigh rate capabilities of 232 C (liquid electrolyte) and 116 C (solid electrolyte), which endows the batteries excellent power densities of 32.8 mW cm-2 and 2.2 W cm-3 (based on the whole solid battery). These are among the highest values reported so far. A wrist band battery is further constructed by using a large conductive cloth woven from the conductive yarns by a commercial weaving machine. It powers various electronic devices successfully, enabling dual functions of wearability and energy storage.

Component Matters: Paving the Roadmap toward Enhanced Electrocatalytic Performance of Graphitic C3N4-Based Catalysts via Atomic Tuning.

Atomically precise understanding of componential influences is crucial for looking into the reaction mechanism and controlled synthesis of efficient electrocatalysts. Herein, by means of comprehensive experimental and theoretical studies, we carefully examine the effects of component dopants on the catalytic performance of graphitic C3N4 (g-C3N4)-based electrocatalysts. The g-C3N4 monoliths with three types of dopant elements (B, P, and S) embedded in different sites (either C or N) of the C-N skeleton are rationally designed and synthesized. The kinetics, intrinsic activity, charge-transfer process, and intermediate adsorption/desorption free energy of the selected catalysts in oxygen reduction reaction and hydrogen evolution reaction are investigated both experimentally and theoretically. We demonstrate that the component aspect within the g-C3N4 motifs has distinct and substantial effects on the corresponding electroactivities, and proper component element engineering can be a viable yet efficient protocol to render the metal-free composites as competent catalysts rivaling the metallic counterparts. We hope that this study may shed light on the empirical trial-and-error exploration in design and development of g-C3N4-based materials as well as other metal-free catalysts for energy-related electrocatalytic reactions.

A Highly Durable, Transferable, and Substrate-Versatile High-Performance All-Polymer Micro-Supercapacitor with Plug-and-Play Function.

A highly durable high-performance all-polymer micro-supercapacitor with plug-and-play function is developed. Through the newly developed technology, these micro-supercapacitors can be transferred to any substrate with all functions well retained.

Photoluminescent Ti3 C2 MXene Quantum Dots for Multicolor Cellular Imaging.

The fabrication of photoluminescent Ti3 C2 MXene quantum dots (MQDs) by a facile hydrothermal method is reported, which may greatly extend the applications of MXene-based materials. Interestingly, the as-prepared MQDs show excitation-dependent photoluminescence spectra with quantum yields of up to ≈10% due to strong quantum confinement. The applications of MQDs as biocompatible multicolor cellular imaging probes and zinc ion sensors are demonstrated.

Multifunctional Energy Storage and Conversion Devices.

Multifunctional energy storage and conversion devices that incorporate novel features and functions in intelligent and interactive modes, represent a radical advance in consumer products, such as wearable electronics, healthcare devices, artificial intelligence, electric vehicles, smart household, and space satellites, etc. Here, smart energy devices are defined to be energy devices that are responsive to changes in configurational integrity, voltage, mechanical deformation, light, and temperature, called self-healability, electrochromism, shape memory, photodetection, and thermal responsivity. Advisable materials, device designs, and performances are crucial for the development of energy electronics endowed with these smart functions. Integrating these smart functions in energy storage and conversion devices gives rise to great challenges from the viewpoint of both understanding the fundamental mechanisms and practical implementation. Current state-of-art examples of these smart multifunctional energy devices, pertinent to materials, fabrication strategies, and performances, are highlighted. In addition, current challenges and potential solutions from materials synthesis to device performances are discussed. Finally, some important directions in this fast developing field are considered to further expand their application.