Towards the all organic Na-ion battery, using naturally occurring amino- and Hydroxy substituted Anthraquinones

This study investigates the redox potential tunability of hydroxy‑ and amino-substituted anthraquinones (AQs) for their potential application in sodium-ion batteries (SIBs). As hydroxy‑AQs are naturally occurring pigments and amino-AQs are commonly used in toners and inks, AQ and its derivatives have the potential to be a cost-effective, abundant, and environmentally friendly cathode material for SIBs. A comparative analysis of ten distinct (di)hydroxy‑ and (di)amino-substituted AQs revealed substantial redox potential shifts of up to 700 mV in solution and 440 mV in a half-cell battery setup, depending on the substitution pattern. The most positive reduction potential in solution was observed for 1,5-dihydroxyanthraquinone (1,5-OH-AQ), while 2,6-diaminoanthraquinone (2,6-NH₂-AQ) exhibited the most negative value. OH-substituted AQs demonstrate anodic shifts, whereas NH₂-substituted AQs induce cathodic shifts, which can be attributed to the combined effects of inductive (-I) and mesomeric (+ M ) influences, as well as intramolecular hydrogen bonding. To further understand the electronic and structural impact of these functional groups, ATR-FTIR analysis was conducted, revealing that the substitution position significantly affects the strength of the carbonyl bonds, leading to shifts in the C = O stretching vibration. Detailed electrochemical investigations, including cyclic voltammetry (CV) and galvanostatic charge/discharge cycling demonstrate that 1,5-OH-AQ and 2,6-NH₂-AQ exhibit distinct and complementary redox properties. Their pronounced potential differences suggest a viable pathway for an all-organic AQ-based SIB, offering a promising alternative for sustainable energy storage.