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

Renewable materials are requested for large scale electrical storage, a coming necessity with the growth of intermittent solar and wind renewable electricity generation. Biopolymers are a source of inexpensive materials, in particular through the use of black liquor from paper production, a waste product. Interpenetrating networks of the biopolymer lignosulfonate (Lig) and conjugated polymer polypyrrole (Ppy) are synthesized by galvanostatic polymerization from pyrrole/lignosulfonate mixture in acidic aqueous electrolyte. Methoxy and phenolic functional group present in the non‐conducting lignosulfonate are converted to quinone groups. The redox chemistry of quinones is used for charge storage, along with charge storage in polypyrrole. A large variation of the electrochemical activity between lignosulfonates obtained from different sources is observed. The charge storage capacities are significantly enhanced by also including another electroactive dopant, anthraquinone sulfonate (AQS). AQS redox peaks act as an internal reference (standard) to probe the redox electrochemistry of Lig. The synthesized Ppy(Lig) and Ppy(Lig‐AQS) electrodes are characterized by cyclic voltammetry, galvanostatic charge‐discharge cycling, electrochemical quartz crystal microbalance, and atomic force microscopy.

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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.

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