Redox Active Polymers as Soluble Nanomaterials for Energy Storage

Area of Science:

• Electrochemistry and Materials Science
• Energy Storage Technologies
• Polymer Science

Background:

• Nonaqueous flow batteries (NRFBs) face challenges with redox active species crossover, leading to capacity fade and underutilization.
• Current membranes struggle to balance fast ion transport with effective separation of anolyte and catholyte.
• Developing new strategies for efficient and stable energy storage is crucial for widespread adoption of alternative energy sources.

Purpose of the Study:

• To introduce redox active polymers (RAPs) as soluble nanoscopic energy storage units for NRFBs.
• To demonstrate the size-exclusion concept for suppressing redox component crossover using RAPs and commercial separators.
• To explore the fundamental electrochemistry of solubilized RAPs and their potential for grid energy storage.

Main Methods:

• Utilized viologen-, ferrocene-, and nitrostyrene-based polymers in various formats.
• Employed electrochemical techniques including voltammetry (macro- and microelectrodes), rotating disk electrode voltammetry, bulk electrolysis, and scanning electrochemical microscopy.
• Investigated the influence of molecular features like redox moiety, size, and backbone structure on RAP electrochemical characteristics.

Main Results:

• RAP solutions demonstrated efficient and reversible energy storage with chemical modularity and size versatility.
• High molecular weight RAPs effectively suppressed crossover when paired with nanoporous separators.
• RAPs exhibit unique electrochemical behavior distinct from small molecules, enabling efficient 3D charge transfer up to ~800 nm radius particles.

Conclusions:

• RAPs provide a promising strategy for overcoming crossover limitations in NRFBs, enhancing performance and stability.
• The fundamental electrochemistry of RAPs offers insights into charge transfer mechanisms and electrolyte interactions in nanostructured redox systems.
• Further investigation into RAP interactions and single-particle electrochemistry can unlock advanced understanding of charge storage mechanisms.