Martin D. Hager

Self-Healing Materials

Self-healing materials are able to partially or completely heal damage inflicted on them, e.g., crack formation; it is anticipated that the original functionality can be restored. This article covers the design and generic principles of self-healing materials through a wide range of different material classes including metals, ceramics, concrete, and polymers. Recent key developments and future challenges in the field of self-healing materials are summarised, and generic, fundamental material-independent principles and mechanism are discussed and evaluated.

Powering up the Future: Radical Polymers for Battery Applications

Our societys dependency on portable electric energy, i.e., rechargeable batteries, which permit power consumption at any place and in any time, will eventually culminate in resource wars on limited commodities like lithium, cobalt, and rare earth metals. The substitution of conventional metals as means of electric charge storage by organic and polymeric materials, which may ultimately be derived from renewable resources, appears to be the only feasible way out. In this context, the novel class of organic radical batteries (ORBs) excelling in rate capability (i.e., charging speed) and cycling stability (>1000 cycles) sets new standards in battery research. This review examines stable nitroxide radical bearing polymers, their processing to battery systems, and their promising performance.

An aqueous, polymer-based redox-flow battery using non-corrosive, safe, and low-cost materials.

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. Redox-flow batteries (RFBs) were first built in the 1940s and are considered a promising large-scale energy-storage technology. A limited number of redox-active materials—mainly metal salts, corrosive halogens, and low-molar-mass organic compounds—have been investigated as active materials, and only a few membrane materials, 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. 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.

Self‐Healing Polymer Coatings Based on Crosslinked Metallosupramolecular Copolymers

Self-healing coating based on metallopolymers are prepared and fully characterized. Iron bisterpyridine complexes are incorporated into a polymer network based on methacrylates, resulting in self-healing properties of these materials. Moreover, the influence of the comonomers on the thermal properties is studied in detail.

Redox‐Flow Batteries: From Metals to Organic Redox‐Active Materials

Abstract Research on redox‐flow batteries (RFBs) is currently experiencing a significant upturn, stimulated by the growing need to store increasing quantities of sustainably generated electrical energy. RFBs are promising candidates for the creation of smart grids, particularly when combined with photovoltaics and wind farms. To achieve the goal of “green”, safe, and cost‐efficient energy storage, research has shifted from metal‐based materials to organic active materials in recent years. This Review presents an overview of various flow‐battery systems. Relevant studies concerning their history are discussed as well as their development over the last few years from the classical inorganic, to organic/inorganic, to RFBs with organic redox‐active cathode and anode materials. Available technologies are analyzed in terms of their technical, economic, and environmental aspects; the advantages and limitations of these systems are also discussed. Further technological challenges and prospective research possibilities are highlighted.

2-(1 H-1,2,3-Triazol-4-yl)-Pyridine Ligands as Alternatives to 2,2'-Bipyridines in Ruthenium(II) Complexes

The synthesis of a variety of 2-(1H-1,2,3-triazol-4-yl)-pyridines by click chemistry is demonstrated to provide straightforward access to mono-functionalized ligands. The ring-opening polymerization of epsilon-caprolactone initiated by such a mono-functionalized ligand highlights the synthetic potential of this class of bidentate ligands with respect to polymer chemistry or the attachment onto surfaces and nanoparticles. The coordination to Ru(II) ions results in homoleptic and heteroleptic complexes with the resultant photophysical and electrochemical properties strongly dependent on the number of these ligands attached to the Ru(II) core.

Metal‐containing Polymers via Electropolymerization

Electropolymerization represents a suitable and well-established approach for the assembly of polymer structures, in particular with regard to the formation of thin, insoluble films. Utilization of monomers that are functionalized with metal complex units allows the combination of structural and functional benefits of polymers and metal moieties. Since a broad range of both electropolymerizable monomers and metal complexes are available, various structures and, thus, applications are possible. Recent developments in the field of synthesis and potential applications of metal-functionalized polymers obtained via electropolymerization are presented, highlighting the significant advances in this field of research.

Self-healing metallopolymers based on cadmium bis(terpyridine) complex containing polymer networks

The utilization of metal–ligand interactions within polymers generates materials which are of interest for several applications, including self-healing materials. In this work we use methacrylate copolymers containing terpyridine moieties in the side chain for the formation of self-healing metallopolymer networks. The materials were synthesized using the reversible addition–fragmentation chain transfer (RAFT) polymerization technique and subsequent crosslinking by the addition of a metal salt, here cadmium(II) salts, with different counter-ions. The influence of the counter-ions on the self-healing process within these structures was analyzed. The research resulted in a new polymeric material featuring a high (intrinsic) healing efficiency at relatively low temperatures (<75 °C).

Synthesis and characterization of TEMPO- and viologen-polymers for water-based redox-flow batteries

Redox-flow batteries that employ redox-active polymers (pRFB) represent a novel energy storage technology requiring innovative materials. Polymers bearing a viologen unit (N,N′-dialkyl-4,4′-bipyridines) or a TEMPO radical are synthesized. Acrylamide, poly(ethyleneglycol) methyl acrylates, di(ethylene glycol) methacrylate and 2-(methacryloyloxy)-N,N,N-trimethylethane ammonium chloride are studied as water-solubility-enhancing comonomers. The rheological and electrochemical properties of these polymers in aqueous solutions are evaluated, revealing poly(1-methyl-1′-(4-vinylbenzyl)-[4,4′-bipyridine]-1,1′-diium dichloride) (P2a) and poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl-co-2-(methacryloyloxy)-N,N,N-trimethylethane ammonium chloride) (P4e) to be most suited as anode and cathode materials, respectively, for a pRFB.

Correlation between scratch healing and rheological behavior for terpyridine complex based metallopolymers

Certain metallopolymers possess the ability to close scratches by a simple thermal treatment. The present study comprehensively explores the structure–property relationship of these materials by variation of the corresponding metal salts. The scratch-healing properties are studied in detail and correlated to the rheological behavior. Rheological measurements are utilized to determine the supramolecular bond life time (τb). A crossover of G′ and G′′ is found for the scratch healing metallopolymers, whereas this is absent in materials displaying no healing under the investigated conditions. Thus, this study provides a first step for the fundamental understanding of the dynamic behavior of metallopolymers and the impact on the self-healing properties. Furthermore, the effect of the chosen cation and anion on the self-healing behavior is illustrated and studied in detail.