Organic redox flow batteries are large-scale energy storage devices that store energy in organic solutions. The key components of the battery are electrolyte, separator and electrodes. Quinone is an organic compound with a highly conjugated structure. Natural quinones include benzoquinone, naphthoquinone, and anthraquinone. Quinones and analogues are structurally designable and have important applications in the field of organic redox flow batteries. Quinones and analogues have good electrochemical reversibility, and their redox mechanism is the reciprocal conversion between enolation and carbonylation promoted by the conjugated structure. During charging, the carbonyl group on the aromatic ring gets electrons and protons to combine and reduce to phenolic hydroxyl group. During discharge, the phenolic hydroxyl group loses electrons and protons and transforms into a carbonyl group. The introduction of quinone and analogues makes the flow battery have the advantages of high capacity, good cyclability, environmental protection, and low cost.
Figure 1. The charge-discharge reaction equation of hydroxyanthraquinone
- Electrode material: Environmentally friendly and durable organic redox flow batteries can be prepared by using quinone organic compounds as the active material of the electrode of the battery. This battery utilizes a fast proton transfer electron coupling process that does not require noble metals as catalysts. In addition, quinone compounds have good chemical stability in acidic solutions. These properties enable quinone-based electrode materials to be applied in high-efficiency non-metal redox batteries, which are inexpensive, environmentally friendly, and sustainable organic non-metal secondary batteries.
- Electrolyte: Organics can be directly extracted from natural organisms or artificially synthesized, and their electrochemical properties and solubility are tunable. Organic matter as electrolyte has the advantages of high power density, diverse structure and environmental protection. Quinones and analogues have stable structures and properties, and can be used as electrolytes to improve the stability and overall performance of batteries.
- Lin K X, Chen Q, Gerhardt. Alkaline quinone flow battery [J]. Science, 2015, 349, 2529-1532.