Redox Polymers: Opportunities and Challenges in their Unique Functionalities

The growing demand for energy-storage devices has raised inevitable concerns regarding the availability of redox-active inorganic compounds and metals. It is expected that some of the inorganic compounds will be replaced by organic redox polymers, which are produced from abundant sources using environmentally benign processes, and they exhibit inherent advantages, including flexibility, processability, and biocompatibility. Redox polymers contain groups that can be reversibly reduced and oxidized by gaining and releasing electrons, respectively, and constitute an emerging class of functional organic materials. This article begins with a retrospective discussion of polymers and their electron exchange concepts, presenting them as old but new materials. The basics of electrochemical redox couples are briefly reintroduced, and the chemical design strategies for extending them to redox polymers are summarized. Subsequently, the efficient and reversible charge propagation and storage in densely populated redox-active sites on soft polymer platforms are discussed. The potential to employ redox polymers in rechargeable charge-storage applications and next-generation devices is discussed, along with the current challenges and prospects. This outlook suggests fundamental questions and proposes interesting topics for redox polymers to facilitate their development as valuable materials for use in sustainable technologies.