Electrolytic water splitting is an effective approach for H 2 mass production. A conventional water electrolyzer concurrently generates H 2 and O 2 in neighboring electrode compartments separated by a membrane, which brings about compromised purity, energy efficiency, and system durability. On the basis of distinct redox electrochemistry, here, we report a system that enables the decoupling of both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) from the electrodes to two spatially separated catalyst bed reactors in alkaline solutions. Through a pair of close-loop electrochemical− chemical cycles, the system operates upon 7,8-dihydroxy-2-phenazinesulfonic acid (DHPS) and ferricyanide-mediated HER and OER, respectively, on Pt/ Ni(OH) 2 and NiFe(OH) 2 catalysts. Near unity faradaic efficiency and sustained production of hydrogen has been demonstrated at a current density up to 100 mA/cm 2 . The superior reaction kinetics, particularly the HER reaction mechanism of DHPS as a robust electrolyte-borne electron and proton carriers, were scrutinized both computationally and experimentally. We anticipate the system demonstrated here would provide an intriguing alternative to the conventional water electrolytic hydrogen production.

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.

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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.