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An affordable, safe, and scalable battery system is presented, which uses organic polymers as the charge-storage material in combination with inexpensive dialysis membranes and an aqueous sodium chloride solution as the electrolyte. An affordable redox-flow battery Redox-flow batteries are seen as a promising technology for storing energy from renewable resources: they are rechargeable and are easily adapted to larger scales simply by increasing the volume of the liquid electrolytes. Most redox-flow batteries are based on metals, usually vanadium, in acidic media, and charge generation is based on ion-selective membranes separating the two electrolytes. Now Ulrich Schubert and colleagues have developed a redox-flow battery that uses organic polymers as the charge-storage material, in combination with inexpensive dialysis membranes and an aqueous sodium chloride solution as the electrolyte. The battery is non-toxic and cheaper to produce than traditional flow batteries. For renewable energy sources such as solar, wind, and hydroelectric to be effectively used in the grid of the future, flexible and scalable energy-storage solutions are necessary to mitigate output fluctuations 1 . Redox-flow batteries (RFBs) were first built in the 1940s 2 and are considered a promising large-scale energy-storage technology 1 , 3 , 4 . A limited number of redox-active materials 4 , 5 , 6 , 7 , 8 , 9 , 10 —mainly metal salts, corrosive halogens, and low-molar-mass organic compounds—have been investigated as active materials, and only a few membrane materials 3 , 5 , 11 , 12 , 13 , 14 , such as Nafion, have been considered for RFBs. However, for systems that are intended for both domestic and large-scale use, safety and cost must be taken into account as well as energy density and capacity, particularly regarding long-term access to metal resources, which places limits on the lithium-ion-based and vanadium-based RFB development 15 , 16 . Here we describe an affordable, safe, and scalable battery system, which uses organic polymers as the charge-storage material in combination with inexpensive dialysis membranes, which separate the anode and the cathode by the retention of the non-metallic, active (macro-molecular) species, and an aqueous sodium chloride solution as the electrolyte. This water- and polymer-based RFB has an energy density of 10 watt hours per litre, current densities of up to 100 milliamperes per square centimetre, and stable long-term cycling capability. The polymer-based RFB we present uses an environmentally benign sodium chloride solution and cheap, commercially available filter membranes instead of highly corrosive acid electrolytes and expensive membrane materials.

The presence of metal centres in synthetic polymers can impart interesting functionality on the resultant material. This Review Article focuses on the use of metal-containing polymers in a diverse range of applications, for example, in emissive and optical materials, in nanomaterials, as sensors, stimuli-responsive gels, catalysts and artifical metalloenzymes. Synthetic polymers containing metal centres are emerging as an interesting and broad class of easily processable materials with properties and functions that complement those of state-of-the-art organic macromolecular materials. A diverse range of different metal centres can be harnessed to tune macromolecular properties, from transition- and main-group metals to lanthanides. Moreover, the linkages that bind the metal centres can vary almost continuously from strong, essentially covalent bonds that lead to irreversible or 'static' binding of the metal to weak and labile, non-covalent coordination interactions that allow for reversible, 'dynamic' or 'metallosupramolecular', binding. Here we review recent advances and challenges in the field and illustrate developments towards applications as emissive and photovoltaic materials; as optical limiters; in nanoelectronics, information storage, nanopatterning and sensing; as macromolecular catalysts and artificial enzymes; and as stimuli-responsive materials. We focus on materials in which the metal centres provide function; although they can also play a structural role, systems where this is solely their purpose have not been discussed.

Healable materials could play an important role in reducing the environmental footprint of our modern technological society through extending the life cycles of consumer products and constructions. However, as most healing processes are carried out by heat alone, the ability to heal damage generally kills the parent material’s thermal and mechanical properties. Here we present a dynamic covalent polymer network whose thermal healing ability can be switched ‘on’ and ‘off’ on demand by light, thereby providing local control over repair while retaining the advantageous macroscopic properties of static polymer networks. We employ a photoswitchable furan-based crosslinker, which reacts with short and mobile maleimide-substituted poly(lauryl methacrylate) chains forming strong covalent bonds while simultaneously allowing the reversible, spatiotemporally resolved control over thermally induced de- and re-crosslinking. We reason that our system can be adapted to more complex materials and has the potential to impact applications in responsive coatings, photolithography and microfabrication. Healable materials are typically repaired by heat, which can affect the properties of the substance. Here the authors report a dynamic covalent polymer network in which light can switch the healing abilities on or off, allowing healing at defined locations without affecting the polymer as a whole.

Biology offers a valuable inspiration toward the development of self-healing engineering composites and polymers. In particular, chemical level design principles extracted from proteinaceous biopolymers, especially the mussel byssus, provide inspiration for design of autonomous and intrinsic healing in synthetic polymers. The mussel byssus is an acellular tissue comprised of extremely tough protein-based fibers, produced by mussels to secure attachment on rocky surfaces. Threads exhibit self-healing response following an apparent plastic yield event, recovering initial material properties in a time-dependent fashion. Recent biochemical analysis of the structure–function relationships defining this response reveal a key role of sacrificial cross-links based on metal coordination bonds between Zn2+ ions and histidine amino acid residues. Inspired by this example, many research groups have developed self-healing polymeric materials based on histidine (imidazole)–metal chemistry. In this review, we provide a detailed overview of the current understanding of the self-healing mechanism in byssal threads, and an overview of the current state of the art in histidine- and imidazole-based synthetic polymers.

Cost- and energy-efficient long-term storage of excess solar energy remains a major bottleneck in the transition to a sustainable society. Here, we present a water-soluble redox-active copolymer containing viologen moieties that can be charged with electrons upon visible light irradiation using a tris[4,4’-bis( tert -butyl)−2,2’-bipyridine]ruthenium(II) complex as chromophore. In the presence of a sacrificial donor, the system achieves charging efficiencies above 80% and fully maintains this state for several days. Subsequent acidification and the addition of various catalysts enable on-demand usage of the stored electrons for proton reduction to hydrogen with up to 72% efficiency. The system further demonstrates reversibility via a simple pH switch, allowing multiple charging, storage, and catalysis cycles without time-consuming polymer isolation. The present study presents a direct on-demand hydrogen evolution method through discharging of a water-soluble polymer that functions as a temporary energy and electron storage material. The study presents a recyclable polymer system that stores solar energy and releases it as hydrogen on demand, offering an efficient and sustainable route for renewable energy storage and fuel generation.

Besides a stable phase, shape‐memory polymers require an additional switchable moiety. In addition to thermal transitions and supramolecular interactions, these units can also be based on covalent bonds. Herein, the use of the reversible thiol‐ene reaction as reversible cross‐linker for the design of shape‐memory polymers is demonstrated. A facile route to polymer networks with a thiol‐ene acceptor and a comonomer (butyl methacrylate or 2‐ethylhexyl methacrylate) cross‐linked by dithiols is introduced. The thermal and mechanical properties of the resulting polymers are characterized in detail. Hereby, the polymers feature excellent shape‐memory behavior with fixity and recovery rates above 90%. This study shows that the thiol‐ene cross‐linker can function as both, the stable and the switchable structural moiety rendering the usage of a covalent cross‐linker unnecessary. This partial reversibility can also be proven by temperature‐depending Raman spectroscopy. The reversible thiol‐ene reaction is used for the design of shape‐memory polymers. Thermal treatment leads to a partial opening of the bonds, which can be monitored by temperature‐dependent Raman spectroscopy. Consequently, the thermal bond activation is correlated with the excellent shape‐memory behavior of the polymers.

Owing to their broad range of redox potential, quinones/hydroquinones can be utilized for energy storage in redox flow batteries. In terms of stability, organic catholytes are more challenging than anolytes. The two-electron transfer feature adds value when building all-quinone flow battery systems. However, the dimerization of quinones/hydroquinones usually makes it difficult to achieve a full two-electron transfer in practical redox flow battery applications. In this work, we designed and synthesized four new hydroquinone derivatives bearing morpholinomethylene and/or methyl groups in different positions on the benzene ring to probe molecular stability upon battery cycling. The redox potential of the four molecules were investigated, followed by long-term stability tests using different supporting electrolytes and cell cycling methods in a symmetric flow cell. The derivative with two unoccupied ortho positions was found highly unstable, the cell of which exhibited a capacity decay rate of ~50% per day. Fully substituted hydroquinones turned out to be more stable. In particular, 2,6-dimethyl-3,5-bis(morpholinomethylene)benzene-1,4-diol (asym-O-5) displayed a capacity decay of only 0.45%/day with four-week potentiostatic cycling at 0.1 M in 1 M H3PO4. In addition, the three fully substituted hydroquinones displayed good accessible capacity of over 82%, much higher than those of conventional quinone derivatives.

By combining a viologen unit and a 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO) radical in one single combi‐molecule, an artificial bipolar redox‐active material, 1‐(4‐(((1‐oxyl‐2,2,6,6‐tetramethylpiperidin‐4‐yl)oxy)carbonyl)benzyl)‐1′‐methyl‐[4,4′‐bipyridine]‐1,1′‐diium‐chloride (VIOTEMP), was created that can serve as both the anode (−0.49 V) and cathode (0.67 V vs. Ag/AgCl) in a water‐based redox‐flow battery. While it mimics the redox states of flow battery metals like vanadium, the novel aqueous electrolyte does not require strongly acidic media and is best operated at pH 4. The electrochemical properties of VIOTEMP were investigated by using cyclic voltammetry, rotating disc electrode experiments, and spectroelectrochemical methods. A redox‐flow battery was built and the suitability of the material for both electrodes was demonstrated through a polarity‐inversion experiment. Thus, an organic aqueous electrolyte system being safe in case of cross contamination is presented. Toward replacing vanadium: By combining a viologen unit and a TEMPO radical in a single molecule, a bipolar, redox‐active material is created that can serve as both the anode and cathode of a water‐based redox‐flow battery (RFB). It mimics the redox states of vanadium salts and can, therefore, simplify the operation of organic RFBs. The material is electrochemically investigated and a test RFB cell is built.

For this paper, the self-healing ability of poly(methacrylate)s crosslinked via reversible urea bonds was studied in detail. In this context, the effects of healing time and temperature on the healing process were investigated. Furthermore, the impact of the size of the damage (i.e., area of the scratch) was monitored. Aging processes, counteracting the self-healing process, result in a decrease in the mechanical performance. This effect diminishes the healing ability. Consequently, the current study is a first approach towards a detailed analysis of self-healing polymers regarding the influencing parameters of the healing process, considering also possible aging processes for thermo-reversible polymer networks.

Polymeric single chloride-ion conductor networks based on acrylic imidazolium chloride ionic liquid monomers AACXImCYCl as reported previously are prepared. The chemical structure of the polymers is varied with respect to the acrylic substituents (alkyl spacer and alkyl substituent in the imidazolium ring). The networks are examined in detail with respect to the influence of the chemical structure on the resulting properties including thermal behavior, rheological behavior, swelling behavior, and ionic conductivity. The ionic conductivities increase (by two orders of magnitude from 10 −6 to 10 −4 S·cm −1 with increasing temperature), while the complex viscosities of the polymer networks decrease simultaneously. After swelling in water for 1 week the ionic conductivity reaches values of 10 −2 S·cm −1 . A clear influence of the spacer and the crosslinker content on the glass transition temperature was shown for the first time in these investigations. With increasing crosslinker content, the T g values and the viscosities of the networks increase. With increasing spacer length, the T g values decrease, but the viscosities increase with increasing temperature. The results reveal that the materials represent promising electrolytes for batteries, as proven by successful charging/discharging of a p(TEMPO-MA)/zinc battery over 350 cycles.