Polypeptide organic radical batteries.

In only a few decades, lithium-ion batteries have revolutionized technologies, enabling the proliferation of portable devices and electric vehicles1, with substantial benefits for society. However, the rapid growth in technology has highlighted the ethical and environmental challenges of mining lithium, cobalt and other mineral ore resources, and the issues associated with the safe usage and non-hazardous disposal of batteries2. Only a small fraction of lithium-ion batteries are recycled, further exacerbating global material supply of strategic elements3-5. A potential alternative is to use organic-based redox-active materials6-8 to develop rechargeable batteries that originate from ethically sourced, sustainable materials and enable on-demand deconstruction and reconstruction. Making such batteries is challenging because the active materials must be stable during operation but degradable at end of life. Further, the degradation products should be either environmentally benign or recyclable for reconstruction into a new battery. Here we demonstrate a metal-free, polypeptide-based battery, in which viologens and nitroxide radicals are incorporated as redox-active groups along polypeptide backbones to function as anode and cathode materials, respectively. These redox-active polypeptides perform as active materials that are stable during battery operation and subsequently degrade on demand in acidic conditions to generate amino acids, other building blocks and degradation products. Such a polypeptide-based battery is a first step to addressing the need for alternative chemistries for green and sustainable batteries in a future circular economy.

Safer Polyurethane Foams with Cyclic Carbonates.

Polyurethanes (PUs) are a class of materials usually synthesized from isocyanates, diols, and water. Water is essential for producing carbon dioxide (CO2 ) which is used for the self-blowing of the foams. Due to safety concerns with the production of isocyanates, alternative chemistries have been evaluated and cyclic carbonate systems have shown great promise. In a recent advancement by Bourguignon, Grignard, and Detrembleur, a cyclic carbonate and diamine system is capable of generating CO2 for self-blowing through hydrolysis of the carbonate-based monomer. The authors demonstrate that with a simple variation of the diamine monomer a wide range of physical and thermo-mechanical properties were achievable. This work represents a significant step towards safer and more environmentally friendly PUs.

Real-time insight into the doping mechanism of redox-active organic radical polymers.

Organic radical polymers for batteries represent some of the fastest-charging redox active materials available. Electron transport and charge storage must be accompanied by ion transport and doping for charge neutrality, but the nature of this process in organic radical polymers is not well understood. This is difficult to intuitively predict because the pendant radical group distinguishes organic radical polymers from conjugated, charged or polar polymers. Here we show for the first time a quantitative view of in situ ion transport and doping in organic radical polymers during the redox process. Two modes dominate: doping by lithium ion expulsion and doping by anion uptake. The dominance of one mode over the other is controlled by anion type, electrolyte concentration and timescale. These results apply in any scenario in which electrolyte is in contact with a non-conjugated redox active polymer and present a means of quantifying doping effects.

Multifunctional Shape-Memory Polymer Foams with Bio-inspired Antimicrobials.

Despite a number of clinically available hemostats, uncontrolled bleeding is the primary cause of trauma-related death. Shape-memory polymer (SMP) foams have a number of desirable properties for use as hemostats, including shape recovery to enable delivery into bleed sites, biocompatibility, and rapid blood clotting. To expand upon this material system, the current work aims to incorporate phenolic acids, which are honey-based antimicrobial agents, into SMP foams. We showed that cinnamic acid (CA) can be utilized as a monomer in SMP synthesis to provide foams with comparable pore structure and retained cytocompatibility. The addition of CA enabled tuning of thermal and shape-memory properties within clinically relevant ranges. Furthermore, the modified foams demonstrated initial and sustained antimicrobial effects against gram-positive and gram-negative bacteria. These multifunctional scaffolds demonstrate potential for use as hemostats to improve upon current hemorrhage treatments and provide a new tool in tuning the biological and material properties of SMP foams.

Recyclable Organic Radical Electrodes for Metal-Free Batteries.

Organic batteries are one of the possible routes for transitioning to sustainable energy storage solutions. However, the recycling of organic batteries, which is a key step toward circularity, is not easily achieved. This work shows the direct recycling of poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl) (PTMA) and poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide) (PTAm) based composite electrodes. After charge-discharge cycling, the electrodes are deconstructed using a solubilizing-solvent and then reconstructed using a casting-solvent. The electrochemical properties of the original and recycled electrodes are compared using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) cycling, from which it is discovered using time-of-flight secondary ion mass spectrometry (ToF-SIMS) that recycling can be challenged by the formation of a cathode electrolyte interphase (CEI). In turn, an additive is proposed to modify the CEI layer and improve the properties after recycling. Last, an anionic rocking chair battery consisting of PTAm electrodes as both positive and negative electrodes is demonstrated, in which the electrodes are recycled to form a new battery. This work demonstrates the recycling of composite electrodes for organic batteries and provides insights into the challenges and possible solutions for recycling the next-generation electrochemical energy storage devices.

Nonconjugated Redox-Active Polymers: Electron Transfer Mechanisms, Energy Storage, and Chemical Versatility.

The storage of electric energy in a safe and environmentally friendly way is of ever-growing importance for a modern, technology-based society. With future pressures predicted for batteries that contain strategic metals, there is increasing interest in metal-free electrode materials. Among candidate materials, nonconjugated redox-active polymers (NC-RAPs) have advantages in terms of cost-effectiveness, good processability, unique electrochemical properties, and precise tuning for different battery chemistries. Here, we review the current state of the art regarding the mechanisms of redox kinetics, molecular design, synthesis, and application of NC-RAPs in electrochemical energy storage and conversion. Different redox chemistries are compared, including polyquinones, polyimides, polyketones, sulfur-containing polymers, radical-containing polymers, polyphenylamines, polyphenazines, polyphenothiazines, polyphenoxazines, and polyviologens. We close with cell design principles considering electrolyte optimization and cell configuration. Finally, we point to fundamental and applied areas of future promise for designer NC-RAPs.

100th Anniversary of Macromolecular Science Viewpoint: Fundamentals for the Future of Macromolecular Nitroxide Radicals.

Macromolecular radicals, radical polymers, and polyradicals bear unique functionalities derived from their pendant radical groups. The increasing need for organic functional materials is driving the growth in research interest in macromolecular radicals for batteries, electronics, memory, and imaging. This Viewpoint summarizes the current state-of-knowledge regarding the macromolecular nitroxide radicals' redox mechanism, conductivity, chain conformation, controlled polymerization, network structure, conjugated forms, and applications. The nitroxide radical group is the focus because it is the most widely studied. Although most literature focuses upon applications, an emerging body of work is highlighting the fundamental physicochemical properties of macromolecular radicals. To this end, this Viewpoint recommends areas of opportunity in fundamental studies and best practices in reporting.

Quantifying internal charge transfer and mixed ion-electron transfer in conjugated radical polymers.

Macromolecular radicals are receiving growing interest as functional materials in energy storage devices and in electronics. With the need for enhanced conductivity, researchers have turned to macromolecular radicals bearing conjugated backbones, but results thus far have yielded conjugated radical polymers that are inferior in comparison to their non-conjugated partners. The emerging explanation is that the radical unit and the conjugated backbone (both being redox active) transfer electrons between each other, essentially "quenching" conductivity or capacity. Here, the internal charge transfer process is quantified using a polythiophene loaded with 0, 25, or 100% nitroxide radicals (2,2,6,6-tetramethyl-1-piperidinyloxy [TEMPO]). Importantly, deconvolution of the cyclic voltammograms shows mixed faradaic and non-faradaic contributions that contribute to the internal charge transfer process. Further, mixed ion-electron transfer is determined for the 100% TEMPO-loaded conjugated radical polymer, from which it is estimated that one triflate anion and one propylene carbone molecule are exchanged for every electron. Although these findings indicate the reason behind their poor conductivity and capacity, they point to how these materials might be used as voltage regulators in the future.

Solution-Processable Thermally Crosslinked Organic Radical Polymer Battery Cathodes.

Organic radical polymers are promising cathode materials for next-generation batteries because of their rapid charge transfer and high cycling stability. However, these organic polymer electrodes gradually dissolve in the electrolyte, resulting in capacity fade. Several crosslinking methods have been developed to improve the performance of these electrodes, but they are either not compatible with carbon additives or compromise the solution processability of the electrodes. A one-step post-synthetic, carbon-compatible crosslinking method was developed to effectively crosslink an organic polymer electrode and allow for easy solution processing. The highest electrode capacity of 104 mAh g-1 (vs. a theoretical capacity of 111 mAh g-1 ) is achieved by introducing 1 mol % of the crosslinker, whereas the highest capacity retention (99.6 %) is obtained with 3 mol % crosslinker. In addition, mass transfer was observed in situ by using electrochemical quartz crystal microbalance with dissipation monitoring. These results may guide future electrode design toward fast-charging and high-capacity organic electrodes.

Shape memory polyurethane-urea foams with improved toughness.

Current vascular aneurysm treatments often require either highly invasive strategy to surgically occlude an aneurysm or endovascular occlusion via metal coils. While endovascular coils are safer, they have limited efficacy. Endovascular coils that are integrated with shape memory polymer (SMP) foams have the potential to improve occlusion and reduce coil risks; however, the mechanical performance and limited homogeneity of SMP foams can hinder their effective use. To address this issue, SMP foams are synthesized using the monomer diethanolamine (DEA) in place of triethanolamine (TEA) to provide improved mechanical properties for medical device applications. Mechanical testing and micro-fracture analysis were performed on DEA and TEA foams. DEA foams show improved toughness and reduced micro-fractures compared to the control. This work presents the utility of DEA in SMP synthesis to enable the potential production of safer aneurysm treatment.

Development of siloxane-based amphiphiles as cell stabilizers for porous shape memory polymer systems.

HYPOTHESIS: Polyurethane foaming surfactants are cell stabilized at the polymer-gas interface during foam blowing to prevent bubble coalescence. Siloxane-based surfactants are typically used to generate a surface tension gradient at the interface. The chemical structure of the hydrophobic and hydrophilic units affects surfactant properties, which can further influence foam morphology. EXPERIMENTS: Siloxane-polyethylene glycol (PEG) ether amphiphiles were synthesized in high yield via hydrosilylation to serve as surfactants for shape memory polymer (SMP) foams. Hydrophobic units consisted of trisiloxane and polydimethyl siloxane, and PEG allyl methyl ether (n=8 or 25) was the hydrophilic component. Upon confirming successful synthesis of the surfactants, their surface tension was measured to study their suitability for use in foaming. SMP foams were synthesized using the four surfactants, and the effects of surfactant structure and concentration on foam morphology were evaluated. FINDINGS: Spectroscopic data confirmed successful siloxane-PEG coupling. All surfactants had a low surface tension of 20-21mN/m, indicating their ability to reduce interfacial tension. SMP foams were successfully fabricated with tunable cell size and morphology as a function of surfactant type and concentration.