Electrochemical characterizations of conducting redox polymers with proton traps : Enabling proton cycling in aprotic systems for high potential energy storage

Abstract: Floods, droughts and unpredictable weather could be the new reality for millions of people in a near future, unless we drastically decrease our greenhouse gas emissions to prevent the global average temperature from increasing even further. Material innovations will most certainly be essential for many of the technical solutions needed in order to tackle environmental issues. One major challenge is how to deal with the massive energy demand, following the average lifestyle of today, in a way that is both reliable and sustainable. Renewable energy sources have a varying output over time, hence cannot meet the demand for electricity by themselves. To buffer between demand and production, new ways to store the renewably produced energy are crucial. From a life cycle aspect conventional battery types are far from sustainable, and, with the increasing number of electronic devices for numerous applications, we need new options.This thesis explores conducting redox polymers (CRPs), which can be utilized as organic cathode materials in high potential energy storage. Hydroquinone (HQ) was applied as the capacity carrying pendant group, and by the introduction of a proton trap functionality the high reduction potential of quinone-proton cycling was achieved also in aprotic electrolytes. The high reduction potential allows for redox matching with the polymer backbone, crucial for CRPs to work as energy storage materials without any additives, and this was studied by in situ conductance with IDA. In situ EQCM was applied in order to examine the cycling chemistry, and the constant mass uptake during the full oxidation cycle (and reverse during the reduction cycle) indicated uptake of charge compensating ions. Further, the proton trap functionality and its effectiveness were investigated by compositional variation, FTIR and variation of electrolyte. In situ UV/Vis was applied in order to study the electronic transitions of the bandgap, the charge carriers and the pendant group redox conversion.The results presented introduce a new route for utilizing protonated forms of quinones as capacity carriers in aprotic media, by incorporating a proton trap in the material. The battery prototypes point to the versatility of the proton trap materials, having reversible proton cycling also when the electrolyte contains metal salts. With dual-ion type batteries the cycling chemistry of the anode is disconnected from the cathode, which allows for free choice of anode material.