Kenichi Oyaizu

Toward Flexible Batteries

clicking here. colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others here. following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles ): February 27, 2013 www.sciencemag.org (this information is current as of The following resources related to this article are available online at http://www.sciencemag.org/content/319/5864/737.full.html version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/content/319/5864/737.full.html#ref-list-1 , 2 of which can be accessed free: cites 11 articles This article 32 article(s) on the ISI Web of Science cited by This article has been http://www.sciencemag.org/content/319/5864/737.full.html#related-urls 4 articles hosted by HighWire Press; see: cited by This article has been http://www.sciencemag.org/cgi/collection/chemistry Chemistry subject collections: This article appears in the following

p- and n-Type Bipolar Redox-Active Radical Polymer: Toward Totally Organic Polymer-Based Rechargeable Devices with Variable Configuration

pand n-Type bipolar organic polymers have attracted remarkable interest in the development of organic-based devices, such as organic light-emitting diodes, organic thin-fi lm transistors, and photovoltaics, because they allow the proper balance of holeand electron-conduction and simplifi cation of device structure. [ 1 ] Bipolarity is mostly carried on separate donor and acceptor sites and a few exceptions are pand n-doped polythiophenes. [ 2 ] Insuffi cient stability of the n-doped state has limited the exploration of bipolar redox-active polymers, which are even accompanied by counterion migration. Stoichiometric bipolar redox activity for charge storage (long term) is challenging, but here we achieved three redox states (n-doped, neutral, and p-doped states) via judicious molecular design of the organic polymers. Recently, we successfully utilized redox polymers bearing robust, redox-active radical pendant groups, such as 2,2,6,6-tetramethylpiperidinyl-oxy (TEMPO) (p-type) [ 3 ] and galvinoxyl (n-type), [ 4 ] as cathodeand anode-active materials, respectively, and demonstrated high power rate capability in a totally organic-based rechargeable battery. We also reported either por n-type redox activity of poly(nitroxylstyrene) switched with substituent electronic effects, [ 5 ] however, these radical polymers did not show any bipolar redox activity, which is even more challenging than n-type redox activity. [ 6 ] Here we focus on redox reactions of nitronylnitroxide ( Figure 1 a ), [ 7 ] stabilized by the conjugated structure of two NO sites and by tuning the electrolyte conditions and report for the fi rst time poly(nitronylnitroxylstyrene) as the bipolar (pand n-dopable) electrode-active material. In this report, we construct two unprecedented battery confi gurations: a) a symmetric confi guration (poleless battery) composed of poly(nitronylnitroxylstyrene) 1 for both electrodes and b) a both n-type electrode confi guration (“rocking-chair-type”) utilizing poly(nitronylnitroxylstyrene) 1 and poly(galvinoxylstyrene) 2 [ 4 ] as the anodeand the cathode-active materials, respectively. A poleless battery confi guration is curious in the interest of simplifying

Nernstian Adsorbate-like Bulk Layer of Organic Radical Polymers for High-Density Charge Storage Purposes

Redox polymer layers with 2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl (TEMPO) groups showed nernstian adsorbate-like electrochemical behaviors up to submicrometer thicknesses, based on a fast charge propagation within the bulk layer and persistency in electrolyte solutions.

Aqueous electrochemistry of poly(vinylanthraquinone) for anode-active materials in high-density and rechargeable polymer/air batteries.

A layer of poly(2-vinylanthraquinone) on current collectors underwent reversible electrode reaction at -0.82 V vs Ag/AgCl in an aqueous electrolyte. A repeatable charging/discharging cycles with a redox capacity comparable to the formula weight-based theoretical density at the negative potential suggested that all of the anthraquinone pendants in the layer was redox-active, that electroneutralization by an electrolyte cation was accomplished throughout the polymer layer, and that the layer stayed on the current collector without exfoliation or dissolution into the electrolyte during the electrolysis. The charging/discharging behavior of the polymer layer in the aqueous electrolyte revealed the capability of undergoing electrochemistry even in the nonsolvent of the pendant group, which offered insight into the nature of the anthraquinone pendants populated on the aliphatic chain. Charging/discharging capability of air batteries was accomplished by using the polymer layer as an organic anode-active material. A test cell fabricated using the conventional MnO(2)/C cathode catalyst exhibited a discharging voltage at 0.63 V corresponding to their potential gap and a charging/discharging cycle of more than 500 cycles without loss of the capacity.

Oxovanadium(III–V) mononuclear complexes and their linear assemblies bearing tetradentate Schiff base ligands: structure and reactivity as multielectron redox catalysts

Abstract This review summarizes the recent advances in the chemistry of oxovanadium(III–V) mononuclear complexes and their linear assemblies bearing tetradentate Schiff base ligands. Structural parameters of the oxovanadium assemblies are compiled, which reveal the preference of specific coordination geometries around vanadium atoms according to the valence state. Emphasis is placed on the catalysis of multielectron redox reactions by oxovanadium(IV) complexes which disproportionate to vanadium(III) and oxovanadium(V) complexes under suitable conditions. Their biological implications and synthetic applications are described.

Radical polymer-wrapped SWNTs at a molecular level: high-rate redox mediation through a percolation network for a transparent charge-storage material.

The functionalization of carbon nanotubes (CNTs) has been widely investigated, [ 1–3 ] and, in particular, in conjunction with redox-active molecules this would lead to potential applications for electronic devices. [ 4 , 5 ] Attachment of redox molecules on CNTs is available due to relatively strong interactions, such as covalent bonding, π – π interactions, and π –cation interactions. [ 6–8 ] However, these interactions often require destructive and severe conditions that damage the CNTs and/or extra functional groups that interfere with the electrochemical and optical properties of the redox-active sites. An effi cient functionalization with a non-destructive interaction is required to maintain the inherent properties of both the CNTs and the redox-active molecules. Polymer wrapping, which interacts in 3D with CNTs by weak interactions, could be one of the best methods for functionalizing CNTs with redox-active molecules. Charge-storage materials or electrode-active materials for rechargeable batteries consisting of organics have been developed using redox-active molecules [ 9 ] and polymers. [ 10–14 ] We have been developing the organic radical battery, [ 10–20 ] utilizing a series of synthesized polymers containing redox-active organic radicals fenced by bulky alkyl groups. [ 15–18 ] Typically poly(2,2,6,6-tetramethylpiperidine-1-oxy-4-yl methacrylate) (PTMA) was employed as the organic cathode-active pendant group. [ 10 ] The PTMA ideally consists of the fl exible polymethacrylate backbone and the spherical pendant 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) group and could be expected to impart the TEMPO’s specifi c redox functionality to its CNT nanocomposite ( Figure 1 a). Here, we describe that PTMA-wrapped single-walled carbon nanotubes (SWNT) provide a high dispersibility of the SWNTs and successfully provide the nanocomposite electrode, which displays both a high electrical conductivity through the SWNT network and a quantitative and remarkably high-rate charge-storage capability while maintaining the high transparency of the nanocomposite. We focused on SWNTs with a diameter of 1–3 nm and a large surface area. To exfoliate the SWNT bundles without

A TEMPO-substituted polyacrylamide as a new cathode material: an organic rechargeable device composed of polymer electrodes and aqueous electrolyte

Poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide) was designed and synthesized as an electrode-active polymer for an organic rechargeable device containing an aqueous electrolyte. The device demonstrated a 1.2 V output voltage, exceeded 2000 charging–discharging cycles, and had a high charging rate performance within 1 min.

Nitroxide radicals as highly reactive redox mediators in dye-sensitized solar cells.

The organic radical 2-azaadamantan-N-oxyl (AZA) used as a stable and highly reactive redox mediator in a dye-sensitized solar cell (DSSC) is reported. AZA exhibits both an appropriate redox potential and significantly high values for the diffusivity, heterogeneous electron-transfer rate, and electron self-exchange reaction rate. These properties give rise to an enhanced electron-transfer mediation which leads to a high fill factor or low cell resistance and thus excellent photovoltaic performance to achieve a conversion efficiency of 8.6%. Organic radicals are usually highly reactive and have been considered unstable and intractable. However, some of these radicals have been converted to stable compounds through chemical modification to provide steric protection around the unpaired electrons and/or resonance structures involving the unpaired electrons. 2,2,6,6-Tetramethylpiperidin-N-oxyl (TEMPO) is a typical example of a stable radical, in which the oxygen-centered unpaired electron is sterically protected by the surrounding tetramethyl groups and is stabilized by the resonance structure of the N O group. Stable radicals have been studied in the field of organic magnetism and as catalytic reagents based on their unpaired electron spin and their electron-releasing and electron-accepting character in redox reactions. For example, TEMPO was applied as an organic, metal-free oxidizing catalyst of primary alcohols. To enhance the catalytic activity, 2-azaadamantan-N-oxyl was also employed, which exhibits a much higher reactivity because of the reduced steric hindrance around its radical center compared to that of TEMPO. Recently, we successfully used radical polymers bearing redox-active TEMPO moieties in their repeating units as a cathode-active organic material and demonstrated an amazingly high power rate capability in an organic secondary battery. The high charging and discharging rates were analyzed and ascribed to fast charge propagation and transport through the TEMPO moieties derived from their reversible and rapid redox reactivity and their efficient electron self-exchange reaction. The reactivity and redox potential of the redox reagents were tunable by the molecular structure of the nitroxide derivatives. DSSCs have recently received much attention because of their ease in wet-chemical fabrication and their still improvable conversion efficiency. In DSSCs, photoexcitation of the dye sensitizer molecule is followed by electron injection into the conduction band of titanium oxide (TiO2) on which the dye is adsorbed. The dye molecule is then regenerated or reduced by a redox mediator in the electrolyte solution. The most widely used mediator is the iodide/triiodide (I /I3 ) redox couple, which is regenerated at the counter electrode. The redox mediator acts as a shuttle transporting the electrons (hole charges) through diffusion in the solution. The charge separation at the interface between TiO2/dye solid phase and the mediator solution and the charge transport in the solution play important roles in the current generation in DSSCs. Recently, attention has focused on the redox mediator of DSSCs, because the open-circuit voltage (Voc) of DSSCs is dominated by the energy difference between the Fermi level of TiO2 and the redox potential of the mediator. One drawback of the iodide mediator is the mismatch of its redox potential (about 0.4 V vs. Ag/AgCl), that is, it has an excess driving force or energy loss of 0.6 V for the dye regeneration process, resulting in a limited Voc value (up to 0.9 V as previously reported). Undesirable corrosion of the electrode metals and the strong visible absorption of the iodide mediator are also problematic. Many redox couples have been explored as alternatives to the iodide redox mediator in the past decade. For example, Spiccia and co-workers used the ferrocene/ferrocenium redox couple and demonstrated 7.5% conversion efficiency by optimizing the additives and the composition of the electrolyte and by synthesizing carbazole derivatives as new dye sensitizers. Redox couples of metal complexes, such as Co/ Co, Cu/Cu, and Ni/Ni, have also been widely investigated. Recently, Gr tzel and co-workers achieved the highest record for the conversion efficiency (12.3%) in DSSCs by incorporating cobalt tris(bipyridyl) complexes as redox couple and appropriately designed porphyrin derivatives as organic dye sensitizers. TEMPO has also been applied as a redox mediator in a DSSC by Gr tzel et al. To search for an appropriate redox potential of the mediator for dye regeneration, we examined a series of TEMPO derivatives and succeeded in improving the Voc by modifying the molecular structure of TEMPO with various 4-substituents. Nitroxide derivatives were further studied as DSSC mediators by other groups. However, the Voc was enhanced at the expense of the short-circuit current [*] Dr. F. Kato, A. Kikuchi, T. Okuyama, Prof. K. Oyaizu, Prof. H. Nishide Department of Applied Chemistry, Waseda University Tokyo 169-8555 (Japan) E-mail: nishide@waseda.jp

Environmentally benign batteries based on organic radical polymers

A radical polymer is an aliphatic organic polymer bearing densely populated unpaired electrons in the pendant robust radical groups per repeating unit. These radicals’ unpaired electrons are characterized by very fast electron-transfer reactivity, allowing reversible charging as the electrode-active materials for secondary batteries. Organic-based radical batteries have several advantages over conventional batteries, such as increased safety, adaptability to wet fabrication processes, easy disposability, and capability of fabrication from less-limited resources, which are described along the fashion of green chemistry.

Redox-active polyimide/carbon nanocomposite electrodes for reversible charge storage at negative potentials: expanding the functional horizon of polyimides

The reversible n-type charge-storage capability of polyimides was significantly enhanced in a polyimide/carbon nanocomposite prepared by cyclodehydration of the corresponding polyamic acid which was solution-processed into a composite layer on an electrode surface with a vapor-grown carbon nanofiber. The stepwise preparation process gave the first polyimide-based electrode-active material with a sufficient dispersion of the polyimide particles at the carbon nanofiber surface, while a simple grinding of the polyimide and the carbon nanofiber gave mixtures without charge retention capability due to gradual dissolution in the reduced state. The polyimide/carbon nanocomposites were characterized by negative redox potentials at −1.36 and −0.76 V vs. Ag/AgCl for poly(4,4′-oxydiphthalimido-1,4-phenylene) (1) and poly(pyromellitimido-1,4-phenylene) (2), respectively, which corresponded to a charging per repeating unit of the neutral polymers to radical polyanions. The 2/carbon nanocomposite underwent further reduction at −1.34 V to produce a dianion per repeating unit, giving rise to a high-density charging with a redox capacity of 185 mAh g−1 based on the formula weight of 2. The typical redox capacity of the electrolyzed nanocomposites amounted to ca. 60% of the formula weight-based capacity, which was still larger than those of typical redox polymers with negative potentials, such as viologen-based polyelectrolytes. Additional advantages originated from the robustness of the polyimide framework, which allowed excellent charging/discharging cyclability. The polyimide/carbon nanocomposite electrodes would be highly promising as anode-active materials in organic rechargeable devices, owing to these excellent redox properties.