Developing sustainable organic electrode materials for energy storage applications is an urgent task.

Two self-doped conjugated polyelectrolytes, having semiconducting and metallic behaviors, respectively, have been blended from aqueous solutions in order to produce materials with enhanced optical and electrical properties. The intimate blend of two anionic conjugated polyelectrolytes combine the electrical and optical properties of these, and can be tuned by blend stoichiometry. In situ conductance measurements have been done during doping of the blends, while UV−vis and EPR spectroelectrochemistry allowed the study of the nature of the involved redox species. We have constructed an accumulation/depletion mode organic electrochemical transistor whose characteristics can be tuned by balancing the stoichiometry of the active material.

We report spectroelectrochemical studies to investigate the charge storage mechanism of composite polypyrrole/lignin electrodes. Renewable bioorganic electrode materials were produced by electropolymerization of pyrrole in the presence of a water-soluble lignin derivative acting as dopant. The resulting composite exhibited enhanced charge storage abilities due to a lignin-based faradaic processes, which was expressed after repeated electrochemical redox of the material. The in-situ FTIR spectroelectrochemistry results show the formation of quinone groups, and the reversible oxidation-reduction of these groups during charge-discharge experiments in the electrode materials. The most significant IR bands include carbonyl absorption near 1705 cm -1 , which is attributed to the creation of quinone moieties during oxidation, and absorption at 1045 cm -1 which is due to hydroquinone moieties.after the discovery of metallic polyacetylene by Shirakawa, McDiarmid, Heeger, et al. 10 A strong interest in the development of new storage devices emerged at this time. The benefits of conductive polymers are their high electrical conductivity, processability, low cost and electrochemical reversibility. This is due to the presence of fast charge transfer in the polymeric chain, associated with intercalation/deintercalation of counter-ions during the redox process. 11,12 For many of these reasons, polypyrrole (PPy) seems to be a good candidate for this purpose, as one of the more stable materials, with relatively high theoretical specific capacity 75 mAh g -1 (with dopant) and a specific energy density ranging from 80 to 390 Wh kg −1 . 13,14 However, PPy doped by small, mobile counteranions such as perchlorates, still suffer from self-discharge, from insufficient charge storage density compared to inorganic materials used in secondary batteries, † These authors contributed equally to this work.

Powering the future, while maintaining a cleaner environment and a strong socioeconomic growth, is going to be one of the biggest challenges faced by mankind in the 21st century. The first step in overcoming the challenge for a sustainable future is to use energy more efficiently so that the demand for fossil fuels can be reduced drastically. The second step is a transition from the use of fossil fuels to renewable energy sources. In this sense, organic electrode materials are becoming increasingly attractive compared to inorganic electrode materials which have reached a plateau regarding performance and have severe drawbacks in terms of cost, safety and environmental friendliness. Using organic composites based on conducting polymers, such as polypyrrole, and abundant, cheap and naturally occurring biopolymers rich in quinones, such as lignin, has recently emerged as an interesting alternative. These materials, which exhibit electronic and ionic conductivity, provide challenging opportunities in the development of new charge storage materials. This review presents an overview of recent developments in organic biopolymer composite electrodes as renewable electroactive materials towards sustainable, cheap and scalable energy storage devices.

Funding Agencies|Knut and Alice Wallenberg Foundation; Wallenberg Scholar grant

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lately. Supercapacitor devices allow a considerable amount of stored electric energy to be delivered rapidly, giving rise to high power capability in conjunction with long cycling life and high reversibility. [4][5][6][7] Nevertheless the demand for higher energy density supercapacitors is increasing, to be used as a storage device for renewable electricity.The development of new materials that improve the efficiency of energy conversion and storage is essential for a sustainable future. [8][9][10] These materials should be renewable, biodegradable, and have low cost. [11] Lignin is the second most abundant biopolymer on Earth, and complies with these characteristics. It is the largest natural source of quinone-aromatics chemical groups that can be employed to store and deliver charges by reversible Faradaic reactions. [12,13] However, the insulating nature of lignin limits the access to these functional redox groups. Therefore, it is necessary to form hybrids with other conductive materials such as conducting polymers [14] or carbon derivatives. [15][16][17] In order to harness the potential of conducting polymers as supercapacitor electrode materials, it is critical to improve their poor long-term stability and to increase their specific capacitance and energy density by fully utilizing the pseudo-capacitive redox processes. [18][19][20] In our previous work, we have constructed electrodes with hybrid materials based on electronic polymers and lignin derivatives. We found that the best combination was poly(3,4-ethylenedioxythiophene) PEDOT/lignin with a specific capacitance of 170 F g −1 . [21] We further investigated the interpenetrating network of poly(aminoanthraquinone) (PAAQ) and PEDOT with increased specific capacitance up to 383 F g −1 . [22] The development of hybrid electrode materials formed by electroactive and conducting components enable supercapacitor devices with intrinsic high specific power and improved energy density. These devices are described as symmetric SCs (SSCs) when both electrodes are identical, and asymmetric SCs (ASCs) when the material compositions of the positive and negative electrodes are different. The optimal performance is expected for asymmetric supercapacitors, because it may be possible to extend the operating voltage window of the cell, and its energy density thus becomes greater than that of the symmetric cells, as a consequence of electrodes operating reversibly in different potential ranges. [19,[23][24][25] A trihybrid bioelectrode composed of lignin, poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(aminoanthraquinone) (PAAQ) is prepared by a two-step galvanostatic electropolymerization, and characterized for supercapacitor applications. Using PEDOT/Lignin as a base layer, followed by the consecutive deposition of PAAQ, the hybrid electrode PEDOT/Lignin/PAAQ shows a high specific capacitance of 418 F g −1 with small self-discharge. This trihybrid electrode material can be assembled into symmetric and asymmetric supercapacitors. The asymmetric supercapacitor uses PED...

A water-soluble conjugated polyelectrolyte, PEDOT-S, is demonstrated to be an excellent hole transport material in several polymer solar cells with different donor HOMOs.