Aqueous organic flow batteries for sustainable energy storage

Abstract

Aqueous Organic Redox Flow Batteries (RFBs) have the potential to address the large-scale need for storing electrical energy from intermittent sources like solar- and wind-based generation. Unlike metal-based redox systems, small organic molecules present the prospect of achieving sustainability, by being synthesizable from abundantly available carbon dioxide, water, nitrogen, sulfur, and renewable energy. This mini-review focuses on the progress and challenges in designing water-based RFBs based on small organic molecules that can address the requirements of large-scale energy storage. Much of the recent research in this area involves discovering new molecular architectures via computational screening, understanding degradation, and cell configurations to address the techno-economic challenges of extraordinary electrochemical durability, recyclability, low cost of precursor materials, and good solubility. Redox materials for the positive side of the cell are notably few. Future research must continue to focus on these techno-economic challenges through rapid materials discovery. • Redox molecules must satisfy competing requirements of durability, low cost, and good solubility. • Specific degradation pathways are avoidable by tuning of electronic and steric factors. • Symmetric cells with mixed electrolyte is a practical solution for mitigating effects of crossover. • The use of sustainable biomaterials and low-cost waste products is an exciting prospect.