Bio-Inspired Isoalloxazine Redox Moieties for Rechargeable Aqueous Zinc-Ion Batteries

Organic electrode materials hold great potential for fabricating sustainable energy storage systems, however, the development of organic redox-active moieties for rechargeable aqueous zinc-ion batteries is still at an early stage. Here, we report a bio-inspired riboflavin-based aqueous zinc-ion battery utilizing an isoalloxazine ring as the redox center for the first time. This battery exhibits a high capacity of 145.5 mAh g⁻¹ at 0.01 A g⁻¹ and a long-life stability of 3000 cycles at 5 A g⁻¹. We demonstrate that isoalloxazine moieties are active centers for reversible zinc-ion storage by using optical and photoelectron spectroscopies as well as theoretical calculations. Through molecule-structure tailoring of riboflavin, the obtained alloxazine and lumazine molecules exhibit much higher theoretical capacities of 250.3 and 326.6 mAh g⁻¹, respectively. Our work offers an effective redox-active moiety for aqueous zinc batteries and will enrich the valuable material pool for electrode design.