Redox-active Polymers Research Articles

A redox-active polymer material for superior capacitive storage in ionic liquid electrolyte

Supercapacitors based on ionic liquid (IL) electrolytes offer realistic possibilities for high-performance and sustainable energy storage systems with their unique electrochemical properties, especially wide operation voltage and high usage security. However, there is still a lack of suitable capacitive-storage electrode materials in IL electrolytes. Herein, we have synthesized a highly redox-active polymer (PDPPZ) material with extended conjugated imine-based backbones for superior capacitive storage. Theoretical calculations, such as localized orbital locator-π (LOL-π) and molecular orbital techniques, reveal extraordinary electron delocalization and excellent electron affinity throughout the highly extended π-conjugated polymeric backbones. As a result, the PDPPZ polymer as an organic electrode possesses a high capacitive storage of 135.6 F g−1 and long-term stability with as low as 0.003% decline per cycle in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) IL electrolyte, evidencing its shining in the electrochemical energy storage field.

Anthraquinone-Quinizarin Copolymer as a Promising Electrode Material for High-Performance Lithium and Potassium Batteries.

The growing demand for cheap, safe, recyclable, and environmentally friendly batteries highlights the importance of the development of organic electrode materials. Here, we present a novel redox-active polymer comprising a polyaniline-type conjugated backbone and quinizarin and anthraquinone units. The synthesized polymer was explored as a cathode material for batteries, and it delivered promising performance characteristics in both lithium and potassium cells. Excellent lithiation efficiency enabled high discharge capacity values of >400 mA g-1 in combination with good stability upon charge-discharge cycling. Similarly, the potassium cells with the polymer-based cathodes demonstrated a high discharge capacity of >200 mAh g-1 at 50 mA g-1 and impressive stability: no capacity deterioration was observed for over 3000 cycles at 11 A g-1, which was among the best results reported for K ion battery cathodes to date. The synthetic availability and low projected cost of the designed material paves a way to its practical implementation in scalable and inexpensive organic batteries, which are emerging as a sustainable energy storage technology.

Electropolymerization of D-A type monomers consisting of mono-triphenylamine moiety for electrochromic devices and supercapacitors

Redox active conjugated polymers have been received great research interest due to their potential applications in electrochromic devices and supercapacitors. In this work, three donor-acceptor (D-A) monomers (TPA-BY, TPAP-BY, TPAT-BY) consisting of single triphenylamine unit were synthesized and further deposited on ITO glass via electrochemical polymerization for electrochromic devices and supercapacitors. The obtained polymer films (PTPA-BY, PTPAP-BY, PTPAT-BY) exhibited reversible redox behavior and obvious color change upon voltage variation, especially the optical contrast of PTAP-BY reaching up to 81% at 720 nm. Moreover, the present novel conjugated polymers showed supercapacitor performance with areal specific capacitance among 2.2 ∼ 3.9 mF·cm−2 at a current density of 0.06 mA·cm−2, guaranteeing their potential application in energy saving smart windows.

Highly redox-active polymer with extensive electron delocalization and optimized molecular orbitals for extraordinary proton storage

Due to the unique “Grotthus mechanism” of the proton as the charge carrier, aqueous proton batteries (APBs) have the potential to become a type of feasible energy storage device with low cost and high security. Organic polymers with tunable molecule structures are promising for APB electrodes, whereas unsatisfactory redox capacity and low electron affinity hinder their real applications. Herein, a highly redox-active polymer, poly(diquinoxalino-phenazine) (PDQPZ), has been designed and synthesized with extended imine-conjugated polymeric backbones. Beneficial from the reasonable molecular configuration, the PDQPZ polymer shows extensive electron delocalization and optimized molecular orbitals with an extremely small LUMO value of −3.26 eV, leading to excellent electron affinity and high redox activity for fast, ultra-stable and extraordinary proton storage, which are further demonstrated by localized orbital locator-π (LOL-π) and iso-chemical shielding surface (ICSS) techniques. As such, the PDQPZ polymer as electrode material possesses a superior proton-storage capacity of 205.2 mAh g−1 and excellent cycling stability after 10,000 cycles with as low as 0.0008% decline per cycle. Multiple in-operando monitoring techniques further confirm highly reversible proton uptake/removal and the protonation pathways are proposed in detail. Finally, a high-performance and long-life APB device has been fabricated and operated over a wide temperature range.

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.

Oxidative-Reductive Near-Infrared Electrochromic Switching Enabled by Porous Vertically Stacked Multilayer Devices.

Here, we demonstrate for the first time the ability of a porous π-conjugated semiconducting polymer film to enable facile electrolyte penetration through vertically stacked redox-active polymer layers, thereby enabling electrochromic switching between p-type and/or n-type polymers. The polymers P1 and P2, with structures diketopyrrolopyrrole (DPP)-πbridge-3,4,-ethylenedioxythiophene (EDOT)-πbridge [πbridge = 2,5-thienyl for P1 and πbridge = 2,5-thiazolyl for P2] are selected as the p-type polymers and N2200 (a known naphthalenediimide-dithiophene semiconductor) as the n-type polymer. Single-layer porous and dense (control) polymer films are fabricated and extensively characterized using optical microscopy, atomic force microscopy, scanning electron microscopy, and grazing incidence wide-angle X-ray scattering. The semiconducting films are then incorporated into single and multilayer electrochromic devices (ECDs). It is found that when a p-type (P2) porous top layer is used in a multilayer ECD, it enables electrolyte penetration to the bottom layer, enabling oxidative electrochromic switching of the P1 bottom layer at low potentials (+0.4 V versus +1.2 V with dense P2). Importantly, when using a porous P1 as the top layer with an n-type N2200 bottom layer, dynamic oxidative-reductive electrochromic switching is also realized. These results offer a proof of concept for development of new types of multilayer electrochromic devices where precise control of the semiconductor film morphology and polymer electronic structure is essential.

Exploring a Redox-Active Ionic Porous Organic Polymer in Environmental Remediation and Electrochromic Application.

Here, we report the design and synthesis of a redox-active multifunctional ionic porous organic polymer iPOP-Bpy with exchangeable Br- ions, incorporating viologen as a redox-active building block. The material shows not only excellent iodine uptake capacity in the vapor phase (540 wt %) but also in the organic (1009.77 mg g-1) and aqueous phases (3921.47 mg g-1) with very fast adsorption kinetics in all cases. The material also shows its utility in being used as a solid-state NH3 vapor sensor as it shows very fast color switching in the presence of NH3 vapor. Furthermore, the material found application as a p-type complementary electrochromic electrode and was fabricated into a bilayer device. Excellent coloration efficiency, high switching speed, and good color contrast were obtained as investigated using bias-dependent optical and spectroelectrochemical studies, paving the way for fabricating power-efficient solid-state electrochromic devices.

Enhanced energy density quasi-solid-state supercapacitor based on an ionic liquid incorporated aqueous gel polymer electrolyte with a redox-additive trimethyl sulfoxonium iodide

Enhancing interfacial redox activities by introducing a redox-active species in electrolytes is a latest strategy to enhance the performance characteristics of supercapacitors. Herein, an aqueous redox-active gel polymer electrolyte (R-GPE) is synthesized by adding a redox-active salt (trimethyl-sulfoxonium iodide, TMSI) in an ionic liquid (1-ethyl-3-methylimidazolium chloride, EMICl), entrapping in a host polymer poly(vinyl alcohol). The free-standing film of R-GPE shows high flexibility and excellent electrochemical properties including high room temperature ionic conductivity (σRT = 15.4 mS cm−1) and wide electrochemical stability window (ESW ~ 2.9 V versus Ag/Ag+), which makes the R-GPE film suitable in supercapacitor application. Two supercapacitors are fabricated using gel polymer electrolytes (without and with TMSI, respectively), and activated carbon electrodes, produced from a bio-waste pollen-cone. Presence of TMSI as redox-additive in R-GPE enhances the performance of the device with almost 5-times higher value of specific capacitance (~613 F g−1) and specific energy (~69 Wh kg−1) as compared to the device with GPE (without TMSI). The supercapacitor cell with R-GPE demonstrates a moderate rate capability. The device offers a ~60 % (i.e. ~357 F g−1) capacitance retention after ~5000 charge-discharge cycles with initial fading of ~18 % and >95 % of Coulombic efficiency.

The role of the electrolyte in non-conjugated radical polymers for metal-free aqueous energy storage electrodes.

Metal-free aqueous batteries can potentially address the projected shortages of strategic metals and safety issues found in lithium-ion batteries. More specifically, redox-active non-conjugated radical polymers are promising candidates for metal-free aqueous batteries because of the polymers' high discharge voltage and fast redox kinetics. However, little is known regarding the energy storage mechanism of these polymers in an aqueous environment. The reaction itself is complex and difficult to resolve because of the simultaneous transfer of electrons, ions and water molecules. Here we demonstrate the nature of the redox reaction for poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide) by examining aqueous electrolytes of varying chao-/kosmotropic character using electrochemical quartz crystal microbalance with dissipation monitoring at a range of timescales. Surprisingly, the capacity can vary by as much as 1,000% depending on the electrolyte, in which certain ions enable better kinetics, higher capacity and higher cycling stability.

Redox-active 2D porous organic polymers for high-performance supercapacitor

Porous organic polymers (POPs) have been received considerable attention due to their advantages of large surface areas, good stability and functionalities, which are considered an ideal electrode material for the energy storage device that has been developed and applied in lithium batteries, zinc ion batteries and supercapacitors. Here we describe the synthesis of four kinds of redox-active 2D POPs via solvothermal Schiff base condensation using aniline oligomers with different chain lengths as building units that exhibit reversible electrochemical processes. Among them, the Tp-AT-POP based on 1,3,5-triformylphloroglucinol (Tp) and aniline trimer (AT) deliver high electrochemical performance mainly contributed by redox units exhibiting high specific capacitance up to 348.3 F/g at a current density of 0.5 A/g and possessing excellent cycling stability of 71% after 5000 cycles. In addition, the Tp-AT-POP is developed to assemble a symmetric supercapacitor with specific capacitances of 167 F/g at 0.3 A/g and good cycling stability. This work provides an efficient strategy for developing the redox-active 2D POPs with aniline oligomer structure for the next-generation advanced high-performance energy storage device.

Extended Conjugation Acceptors Increase Specific Energy Densities in π-Conjugated Redox Polymers

Organic materials are a sustainable alternative to replace inorganic transition metal-based cathodes in rechargeable intercalation batteries. Among the possible redox active organic materials, conjugated polymers with multiple redox sites per repeat unit are expected to afford high energy and power densities while being resistant to dissolution when in contact with battery electrolytes. However, accessing the full capacity of polymeric electrodes while ensuring electrochemical reversibility has been challenging. Using diketopyrrolopyrrole (DPP)-based donor–acceptor (D–A) polymers as model systems and complementary electrochemical experiments and first-principles calculations, we show that conjugated backbone moieties that minimize charge localization on the electron accepting repeat units lead to near theoretical discharge capacities. Further, the capacity enhancement is associated with better rate performance and improved electrochemical stability of the polymer over prolonged cycling. Our work suggests that charge density on the electron accepting moiety is a potential descriptor for rationally designing redox-active polymer electrodes that afford high discharge capacities along with a long cycle life.

Acceptor properties of "carbon nanotubes-redox-active polymer based on bovine serum albumin modified with ferrocenecarboxaldehyde" composite for creating a BOD biosensor with Blastobotrys adeninivorans BKM Y-2677 yeast.

The possibility of using a composite material based on bovine serum albumin (BSA) covalently bonded with ferrocenecarboxaldehyde and containing carbon nanotubes (CNT) for the immobilization of Blastobotrys adeninivorans BKM Y-2677 (B. adeninivorans) yeast is discussed. The optimal ratio of ferrocenecarboxaldehyde to BSA for the redox-active polymer synthesis is 1:2, since the heterogeneous electron transfer constant is 0.45 ± 0.01s-1. When carbon nanotubes (CNTs) are added to this polymer, the heterogeneous electron transfer constant increases: at a CNT specific density of 2.5µg/mm2, it reaches a maximum value of 0.55 ± 0.01s-1. The addition of CNTs into the conducting system leads to increasing of the rate constant of interaction redox species with B. adeninivorans yeast by an order: the rate constant of interaction between B. adeninivorans yeast and electroactive particles in a redox-active polymer is 0.056 ± 0.005 dm3/g × s and in a composite material based on CNTs is 0.51 ± 0.02 dm3/g × s. The yeast specific density at the electrode of 0.1mg/mm2 and electrolyte pH of 6.2 was chosen as the working value for the receptor system operation. Immobilized in a composite material, yeast oxidizes a wider range of substrates compared with a similar receptor element based on the ferrocene mediator. The biosensors formed on the basis of hybrid polymers have a high sensitivity with a lower limit of determined concentrations of 1.5mg/dm3 with an assay time of 5min and a high correlation (R = 0.9945) with the results of the standard method for determining biochemical oxygen demand (BOD) in nine real surface water samples of the Tula region.

High-capacity potassium-ion batteries using new rigid backbone quinone-based polymer electrode materials

We report the synthesis and electrochemical study of three quinone-based ladder-type redox-active polymers. These materials were applied as electrode materials in potassium half-cells and delivered high specific discharge capacities of up to 268 mAh g−1 at 0.66 A g−1. Using concentrated diglyme-based electrolyte formulation allowed us to suppress capacity fading and enable stable charge-discharge cycling of the batteries. The designed materials represent promising electrode materials for emerging scalable organic potassium-ion battery technology.

Redox-Active Polymers as Robust Electron-Shuttle Co-Catalysts for Fast Fe3+/Fe2+ Circulation and Green Fenton Oxidation.

Accelerating the rate-limiting Fe3+/Fe2+ circulation in Fenton reactions through the addition of reducing agents (or co-catalysts) stands out as one of the most promising technologies for rapid water decontamination. However, conventional reducing agents such as hydroxylamine and metal sulfides are greatly restricted by three intractable challenges: (1) self-quenching effects, (2) heavy metal dissolution, and (3) irreversible capacity decline. To this end, we, for the first time, introduced redox-active polymers as electron shuttles to expedite the Fe3+/Fe2+ cycle and promote H2O2 activation. The reduction of Fe3+ mainly took place at active N-H or O-H bonds through a proton-coupled electron transfer process. As electron carriers, H atoms at the solid phase could effectively inhibit radical quenching, avoid metal dissolution, and maintain long-term reducing capacity via facile regeneration. Experimental and density functional theory (DFT) calculation results indicated that the activity of different polymers shows a volcano curve trend as a function of the energy barrier, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap, and vertical ionization potential. Thanks to the appropriate redox ability, polyaniline outperforms other redox-active polymers (e.g., poypyrrole, hydroquinone resin, poly(2,6-diaminopyridine), and hexaazatrinaphthalene framework) with a highest iron reduction capacity up to 5.5 mmol/g, which corresponds to the state transformation from leucoemeraldine to emeraldine. Moreover, the proposed system exhibited high pollutant removal efficiency in a flow-through reactor for 8000 bed volumes without an obvious decline in performance. Overall, this work established a green and sustainable oxidation system, which offers great potential for practical organic wastewater remediation.

Electrolytes in Organic Batteries.

Organic batteries using redox-active polymers and small organic compounds have become promising candidates for next-generation energy storage devices due to the abundance, environmental benignity, and diverse nature of organic resources. To date, tremendous research efforts have been devoted to developing advanced organic electrode materials and understanding the material structure-performance correlation in organic batteries. In contrast, less attention was paid to the correlation between electrolyte structure and battery performance, despite the critical roles of electrolytes for the dissolution of organic electrode materials, the formation of the electrode-electrolyte interphase, and the solvation/desolvation of charge carriers. In this review, we discuss the prospects and challenges of organic batteries with an emphasis on electrolytes. The differences between organic and inorganic batteries in terms of electrolyte property requirements and charge storage mechanisms are elucidated. To provide a comprehensive and thorough overview of the electrolyte development in organic batteries, the electrolytes are divided into four categories including organic liquid electrolytes, aqueous electrolytes, inorganic solid electrolytes, and polymer-based electrolytes, to introduce different components, concentrations, additives, and applications in various organic batteries with different charge carriers, interphases, and separators. The perspectives and outlook for the future development of advanced electrolytes are also discussed to provide a guidance for the electrolyte design and optimization in organic batteries. We believe that this review will stimulate an in-depth study of electrolytes and accelerate the commercialization of organic batteries.

TEMPO-Modified Polymethacrylates as Mediators in Electrosynthesis: Influence of the Molecular Weight on Redox Properties and Electrocatalytic Activity.

Homogeneous catalysts ("mediators") are frequently employed in organic electrosynthesis to control selectivity. Despite their advantages, they can have a negative influence on the overall energy and mass balance if used only once or recycled inefficiently. Polymediators are soluble redox-active polymers applicable as electrocatalysts, enabling recovery by dialysis or membrane filtration. Using anodic alcohol oxidation as an example, we have demonstrated that TEMPO-modified polymethacrylates (TPMA) can act as efficient and recyclable catalysts. In the present work, the influence of the molecular size on the redox properties and the catalytic activity was carefully elaborated using a series of TPMAs with well-defined molecular weight distributions. Cyclic voltammetry studies show that the polymer chain length has a pronounced impact on the key-properties. Together with preparative-scale electrolysis experiments, an optimum size range was identified for polymediator-guided sustainable reaction control.

Radical polymeric p-doping and grain modulation for stable, efficient perovskite solar modules.

High-quality perovskite light harvesters and robust organic hole extraction layers are essential for achieving high-performing perovskite solar cells (PSCs). We introduce a phosphonic acid-functionalized fullerene derivative in mixed-cation perovskites as a grain boundary modulator to consolidate the crystal structure, which enhances the tolerance of the film against illumination, heat, and moisture. We also developed a redox-active radical polymer, poly(oxoammonium salt), that can effectively p-dope the hole-transporting material by hole injection and that also mitigates lithium ion diffusion. Power conversion efficiencies of 23.5% for 1-square-centimeter mixed-cation-anion PSCs and 21.4% for 17.1-square-centimeter minimodules were achieved. The PSCs retained 95.5% of their initial efficiencies after 3265 hours at maximum power point tracking under continuous 1-sun illumination at 70° ± 5°C.

Mechanism of CO2 Capture and Release on Redox-Active Organic Electrodes

The mechanism of faradaic electro-swing for CO2 capture/release on a redox-active organic electrode is studied from the point of view of realizing a reversible process for CO2 separation. First, the cyclic voltammograms (CVs) of two redox-active organic monomers, anthraquinone (AQ) and 2,1,3-benzothiadiazole (BTZ), were measured under a CO2 atmosphere. The waveforms of CVs of the two redox-active organic monomers are altered under a CO2 atmosphere relative to a N2 atmosphere. There is a change in the number of redox waves from two to one for AQ and a change from reversible to irreversible waves for BTZ. To further understand the mechanisms of CO2 capture/release on redox-active organic compounds, redox-active polymer electrodes coated with polyanthraquinone (PAQ) and polybenzothiadiazole (PBTZ) were investigated using a spectroscopic analysis known as in situ attenuated total reflectance–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) as well as density functional theory (DFT) calculations. The CVs measured with two redox-active polymer electrodes have more positive shifts of reduction potentials for PAQ and PBTZ under a CO2 atmosphere than under an N2 atmosphere, as measured versus Ag/AgNO3: −1.8 and −1.4 V → −1.4 and −0.9 V for PAQ and −2.5 V → −2.1 and −1.9 V for PBTZ. In addition, the oxidation current on the PBTZ electrode disappears only under a CO2 atmosphere. DFT calculations indicate that the positive shifts of reduction potentials in the two electrodes under CO2 conditions are due to an exergonic adsorption reaction of CO2 onto the redox-active organic compounds. To clarify the reaction behavior between CO2 and the redox-active organic electrode, an ATR–SEIRAS spectroscopic analysis was performed. Infrared peaks are observed at 2200 and 2100 cm–1 for PAQ and PBTZ electrodes, respectively, under a CO2 atmosphere, which have been confirmed by measurements under a 13CO2 atmosphere to have adsorbed CO2. The wavenumbers corresponding to the CO2 molecules adsorbed on the two electrodes are different. These findings indicate that one electron reduction and CO2 adsorption for each redox-active organic compound are occurring simultaneously. The calculated adsorption energy of CO2 for two redox-active organic electrodes indicates that the adsorption energies of two CO2 molecules for AQ and BTZ are −7.3 and −36.3 kJ/mol. The larger adsorption energy in BTZ than that in AQ is clearly related to the disappearance of the oxidation current. However, both adsorption energies indicating adsorption of CO2 onto organic units are less than the covalent bond energies of common organic compounds, indicating that such weak adsorptions are suitable for the faradaic electro-swing of CO2 capture/release on the redox-active organic units.

Structural organic battery cathodes comprised of organic redox active polymers, reduced graphene oxide, and aramid nanofibers

A fast-charging structural cathode comprised of a redox-active polymer PTMA–GMA coated on a rGO/BANF platform that exhibits an excellent specific power (∼4310 W kg−1 at 25C-rate) and specific modulus (∼4.33 GPa cm3 g−1).

Charge-transport kinetics of dissolved redox-active polymers for rational design of flow batteries.

Charge-transport kinetics of redox-active polymers is essential in designing electrochemical devices. We formulate the homogeneous and heterogeneous charge-transfer processes of the redox-active polymers dissolved in electrolytes. The critical electrochemical parameters, the apparent diffusion coefficient of charge transport (D app) and standard electrochemical reaction constant (k 0), are estimated by considering the physical diffusion D phys of polymer chains (D app, k 0 ∝ D phys). The models are validated with previously reported compounds and newly synthesized hydrophilic macromolecules. Solution-type cells are examined to analyze their primary responses from the electrochemical viewpoints.