Schiff-bases for sustainable battery and supercapacitor electrodes

The quest for more efficient ways to store electrical energy prompted the development of different storage devices over the last decades. This includes but is not limited to different battery concepts and supercapacitors. However, modern batteries rely on electrochemical principles that often involve transition metals which can for instance suffer from toxicity or limited availability. More sustainable alternatives are needed. This sparked the search for organic electrode materials. Nevertheless, compared to their inorganic counterparts, organic electrode materials remain less intensely investigated. Besides the often more complicated electrochemical principles, one likely reason for that are the complex synthetic skills required to develop novel organic materials. Here we review materials synthesized by an old and comparably simple reaction from the field of organic chemistry, namely Schiff-base formation. This reaction can often yield materials under relatively mild conditions, making them especially interesting for the formation of sustainable electrodes. The main weakness of Schiff-base materials, susceptibility to hydrolysis, is of limited concern in most of the battery systems as they mostly anyways require water-free conditions. This review gives an overview of some selected nanomaterials obtained from Schiff-base formation as well as their carbonized derivatives which are of interest for energy storage. Firstly, the general chemistry of Schiff-bases is introduced, followed by an in-depth survey of the most important breakthroughs in the formation of organic battery electrodes that involve materials based on Schiff-base reaction. Lastly, an outlook considering the main hurdles as well as future perspectives of this research area is given.