• Energy Research

The electrochemical reduction and oxidation of cyclohexanedione is evaluated for the first time as the negative electrode reaction in an organic redox flow battery. Electrochemical characterization indicates that the redox reaction of cyclohexanedione is a proton-coupled electron transfer process with quasi-reversible behavior in acidic media (pH 2 M) and exhibit reduction process with up to 4 electrons transferred.\ud

DFT calculations reveal interesting structure–property relationships of the redox potentials of phenazines in non-aqueous media.

Organic macromolecules bearing redox-active units are projected to be promising candidates as safe and sustainable alternatives to current inorganic intercalation electrodes in Li-ion batteries (LIBs). Although a range of redox polymers with various sizes, architectures, and topologies have been successfully evaluated in LIBs, cost-effective polymerization routes toward their synthesis are rarely considered. Here, a cost-effective synthetic route was employed to synthesize a hypercrosslinked polymeric network bearing a representative p-type organic redox functionality known as phenothiazine. This hypercrosslinked phenothiazine polymer (named IEP-29) was subsequently evaluated as an organic cathode in a lithium battery. The hereby used “knitting” polymerization technique operating through the Friedel–Crafts mechanism allowed us to produce the final atom-economic polymeric network. The material features a remarkably high density of phenothiazine redox units connected by only allylic carbons (−CH2−), unlike bulky crosslinkers used for the production of common hyperbranched/porous polymers. The IEP-29 cathode delivered high capacity (106 mAh g–1 at 0.5C), close to the theoretical value, high potential output (3.6 V vs Li/Li+), excellent rate capability (60 mAh g–1 at 15C), and good cycle stability (79% capacity retention after 1000 cycles at 2C). Since the hereby used “knitting” method is a quite facile method to polymerize low-cost materials in high yields, the findings pave the way for valorization of the organic electrode materials for scalable applications without compromising the performance. Authors thank the European Union's Horizon 2020 under the Мarie Skłodowska-Curie Grant agreement (Grant No 860403) and the Spanish Government through MCIN/AEI/FEDER (PID2021-124974OB-C21 and PID2022-141688OB-I00) and Maria de Maetzu Unit of Excellence award (Ref: CEX2019-000931-M) for the funding. NP appreciates fellowship

Redox-flow batteries, based on their particular ability to decouple power and energy, stand as prime candidates for cost-effective stationary storage, particularly in the case of long discharges and long storage times. Integration of renewables and subsequent need for energy storage is promoting effort on the development of mature and emerging redox-flow technologies. This review aims at providing a critical analysis of redox-flow technologies that can potentially fulfill cost requirements and enable large scale storage, mainly aqueous based systems. A comprehensive overview of the status of those technologies, including advantages and weaknesses, is presented. Compiled data on the market permeability, performance and cost should serve, together with the perspective included, to understand the different strategies to reach the successful implementation, from component development to innovative designs. European Union under HIGREEW, Affordable High-performance Green Redox Flow batteries (Grant Agreement no. 875613) and CuBER, Copper-Based Flow Batteries for energy storage renewables integration (Grant agreement no: 875605) projects. Basque Government (GV-ELKARTEK-2020 KK-2020/00078), Spanish MINECO (RTI2018-099228-A-I00 and RYC2018-026086-I (Ramon y Cajal fellowship) E.V.) and CDTI (Centro para el Desarrollo Tecnológico Industrial, CER-20191006) are also acknowledged for funding this work. R.M. thanks the European Research Council (ERC) through “MFreeB” project (grant agreement no. 726217)

New redox-active polymer nanoparticles present that the redox potential of the catechol group is affected by the presence of the pyridine. This positive potential gain is associated to the proton trap effect, which benefits the performance of lithium-ion–polymer batteries.

Abstract A series of new sequenced sulfonated naphthalenic polyimides were synthesized containing a flexible aromatic–aliphatic diamine. The obtained membranes present the advantage of being soluble in N -methyl pyrrolidone (NMP) which is a less toxic solvent than the previously used m -cresol. In this work, we report on the solvent and acidification method effects on the properties of the membranes such as density, water uptake, proton conductivity as well as on the performance of these membranes in fuel cell operation. The membranes prepared from NMP solution and acidified with ion-exchange resins give the best results. They have good mechanical properties as well as high ionic conductivity (14.4 × 10 −2 S cm −1 at 80 °C) and good performances as proton exchange membrane (PEM) in fuel cell at 70 °C.