The introduction of Prussian blue (PB), an inexpensive pigment material, elegantly breaks the solubility limit of the [Fe(CN) 6 ] 4À/3À electrolyte, and substantially boosts the capacity via an off-electrode chemical reaction. In the reversible redoxtargeting reaction cycles, PB acts as the energy reservoir, while [Fe(CN) 6 ] 4À/3À plays a role in mediating the reactions between the electrode and storage tank. The volumetric capacity surpasses other reported [Fe(CN) 6 ] 4À/3À -based and most other organic aqueous redox flow batteries.

Aqueous organic redox flow batteries (AORFBs) have received considerable attention for large‐scale energy storage. Quinone derivatives, such as 9,10‐anthraquinone‐2,7‐disulphonic acid (2,7‐AQDS), have been explored intensively owing to potentially low cost and swift reaction kinetics. However, the low solubility in pH‐neutral electrolytes restricts their application to corrosive acidic or caustic systems. Herein, the single molecule redox‐targeting reactions of 2,7‐AQDS anolyte are presented to circumvent its solubility limit in pH‐neutral electrolytes. Polyimide was employed as a low‐cost high‐capacity solid material to boost the capacity of 2,7‐AQDS electrolyte to 97 Ah L−1. Through in situ FTIR spectroscopy, a hydrogen‐bonding mediated reaction mechanism was disclosed. In conjunction with NaI as catholyte and nickel hexacyanoferrate as the catholyte capacity booster, a single‐molecule redox‐targeting reaction‐based full cell with energy density up to 39 Wh L−1 was demonstrated.

Zinc–air batteries (ZABs) have recently attracted revived interest. However, critical issues pertaining to the labile zinc anode and sluggish air cathode have yet to be adequately addressed. Here, we demonstrate a redox-mediated zinc–air fuel cell (RM-ZAFC) to tackle the above problems. Upon operation, the complex cobalt triisopropanolamine serves as an electrolyte-borne electron carrier and homogeneous catalyst to boost the 4e– oxygen reduction reaction in a separate gas diffusion tank, which makes the system free of a sophisticated air electrode. With mediation by the ultrafast reaction with a phenazine derivative, zinc could be liberated from the electrode to a separate “fuel” tank at high utilization (>90%), making it feasible to be “refueled” after it is depleted. Above all, RM-ZAFC has the combined advantages of both ZABs and alkaline fuel cells and can operate with high energy density, good flexibility, scalability and safety at low cost and thus is promising for various energy storage applications.

Aqueous organic redox flow batteries (AORFBs) are a promising technology for large-scale electricity energy storage to realize efficient utilization of intermittent renewable energy. In particular, organic molecules are a class of metal-free compounds that consist of earth-abundant elements with good synthetic tunability, electrochemical reversibility and reaction rates. However, the short cycle lifetime and low capacity of AORFBs act as stumbling blocks for their practical deployment. To circumvent these issues, here, we report molecular engineered dihydroxyanthraquinone (DHAQ)-based alkaline electrolytes. Via computational studies and operando measurements, we initially demonstrate the presence of a hydrogen bond-mediated degradation mechanism of DHAQ molecules during electrochemical reactions. Afterwards, we apply a molecular engineering strategy based on redox-active polymers to develop capacity-boosting composite electrolytes. Indeed, by coupling a 1,5-DHAQ/poly(anthraquinonyl sulfide)/carbon black anolyte and a [Fe(CN)6]3−/4− alkaline catholyte, we report an AORFB capable of delivering a stable cell discharge capacity of about 573 mAh at 20 mA/cm2 after 1100 h of cycling and an average cell discharge voltage of about 0.89 V at the same current density.

Zinc-based redox flow battery is regarded as one of the most promising electricity storage systems for large-scale applications. However, dendrite growth and the formation of “dead zinc” of zinc electrodes...